integration of humic acid with nitrogen for improving yield of ...

INTEGRATION OF HUMIC ACID WITH

NITROGEN FOR IMPROVING YIELD OF

MAIZE GENOTYPES

BY

SHAD ALI KHAN

(Reg. No. 12S-UH-29)

Doctor of Philosophy

in

Agriculture (Agronomy)

DEPARTMENT OF AGRICULTURAL SCIENCES

UNIVERSITY OF HARIPUR

KHYBER PAKHTUNKHWA-PAKISTAN

FEBRUARY, 2017

INTEGRATION OF HUMIC ACID WITH

NITROGEN FOR IMPROVING YIELD OF

MAIZE GENOTYPES

BY

SHAD ALI KHAN

(Reg. No. 12S-UH-29)

A dissertation submitted in partial fulfillment of the

requirements for the degree of

Doctor of Philosophy

in

Agriculture (Agronomy)




FEBRUARY, 2017

INTEGRATION OF HUMIC ACID WITH NITROGEN FOR

IMPROVING YIELD OF MAIZE GENOTYPES BY

SHAD ALI KHAN

A dissertation submitted to University of Haripur in partial fulfillment of the requirements for

the degree of

DOCTOR OF PHILOSOPHY IN AGRICULTURE

(AGRONOMY)

Approved by:

______________________ Chairman, Supervisory Committee

Dr. Sami Ullah Khan

Assistant Professor

______________________ Member (Major Field)

Prof. Dr. Ayub Khan

______________________ Member (Other Field)

Dr. Ali Raza Gurmani

Associate Professor

______________________ Chairman/Convener, Board of Studies

Prof. Dr. Ayub Khan

______________________ Dean,

Prof. Dr. Abid Farid Faculty of Basic and Applied Sciences

______________________ Director,

Dr. Shah Masaud Khan Advance Studies and Research Board




FEBRUARY, 2017

Certificate of Approval

This is to certify that the research work presented in this thesis, entitled “Integration of humic

acid with nitrogen for improving yield of maize genotypes” conducted by Mr. Shad Ali Khan

under the supervision of Dr. Sami Ullah Khan. No part of this thesis has been submitted

anywhere else for any other degree. This thesis is submitted to the Department of Agronomy,

The University of Haripur, Haripur in partial fulfillment of the requirements for the degree of

Doctor of Philosophy in the Field of Agronomy, Department of Agronomy, The University of

Haripur, Haripur.

Student Name: Mr. Shad Ali Khan Signature:____________________

Examination Committee:

a) External Examiner 1: Signature:____________________

PROF. Dr. ASGHARI BANO,

Department of Biosciences,

University of Wah,

Wah Cantt

b) External Examiner 2: Signature:____________________

PROF. DR. FAYYAZ UL HASSAN,

Department of Agronomy, PMAS

Arid Agriculture University,

Rawalpindi

c) Internal Examiner 3: Signature:____________________

DR. SAMI ULLAH KHAN

Assistant Professor,

Department of Agronomy

The University of Haripur

Supervisor: Dr. Sami Ullah Khan Signature:____________________

HoD, Agronomy: Dr. Sami Ullah Khan Signature:____________________

Dated: November 16, 2018


IMPROVING YIELD OF MAIZE GENOTYPES

BY

SHAD ALI KHAN

THESIS APPROVED BY:

EXTERNAL EXAMINER:

________________________ Prof. Dr. John Cardina

Horticulture and Crop Science,

116 Guorley Hall OARDC-Wooster,

Wooster, OH 44691

USA


IMPROVING YIELD OF MAIZE GENOTYPES

BY

SHAD ALI KHAN

THESIS APPROVED BY:

EXTERNAL EXAMINER:

_______________________ Prof. Dr. Jinlin Zhang,

School of Pastoral Agriculture Science

and Technology,

Lanzhou University, 222 Tianshui S Rd, Chengguan

Qu, Lanzhou Shi, Gansu Sheng, China

AUTHOR’S DECLARATION

I Shad Ali Khan here by state that my PhD thesis titled “INTEGRATION OF HUMIC ACID

WITH NITROGEN FOR IMPROVING YIELD OF MAIZE GENOTYPES” is my own

work and has not been submitted previously by me for taking any degree from this university

(The University of Haripur) or anywhere else in the country/world.

At any time if my statement is found to be incorrect even after my Graduation, the university

has the right to withdraw my PhD degree.

Shad Ali Khan

Date: 16-11-2018

PLAGIARISM UNDERTAKING

I solemnly that research work presented in the thesis titled “INTEGRATION OF HUMIC

ACID WITH NITROGEN FOR IMPROVING YIELD OF MAIZE GENOTYPES” is solely

my research work with no significant contribution from any other person. Small

contribution/help whatever taken has been duly acknowledged and that complete thesis has

been written by me.

I understand that zero tolerance policy of the HEC and the University (The University of

Haripur) towards plagiarism. Therefore, I as an author of the above titled thesis, declare that

no portion of my thesis has been plagiarized and any material used as reference is properly

referred/cited.

I undertake that, if I am found guilty of any formal plagiarism in the above titled thesis even

after award of PhD degree, the university reserves the rights to withdraw/revoke my PhD

degree and that HEC and the university has the right to publish my name on the HEC/University

Website on which names of students are placed who submitted plagiarized thesis.

Student/Author Signature: --------------------------

Name: Shad Ali Khan

DEDICATED

To

My Sweet Parents

Family Members

Who always prayed for my success in this world and

Hereafter

&

Teachers

Whose instructions, guidelines and suggestions were a great

source of learning and encouragement for me throughout my

study.

TABLE OF CONTENTS

S. NO. TITLE PAGE NO.

LIST OF ABBREVIATIONS ..........................................................................i

LIST OF TABLES ...........................................................................................ii

LIST OF FIGURES ..........................................................................................viii

ACKNOWLEDGEMENTS ..............................................................................xiii

ABSTRACT ...................................................................................................xiv

1. INTRODUCTION......................................................................................... ...1

2. REVIEW OF LITERATURE ..................................................................... ...6

2.1 Humic acid ......................................................................................... ...6

2.1.1 The importance of humic acid ................................................ ...6

2.1.2 Humic acid and soil physio chemical properties .................... ...7

2.1.3 The effect of humic acid on N and P nutrients ....................... ...8

2.1.4 The role of humic acid in crop production .............................. ...8

2.1.4.1 Humic acid and maize phenology ............................... ...8

2.1.4.2 Humic acid and maize physiological growth indices . ...9

2.1.4.3 Humic acid and maize yield ........................................ ...10

2.1.4.4 Humic acid and maize quality ..................................... ...11

2.1.4.5 Humic acid and nitrogen use efficiency (NUE) .......... ...12

2.1.4.6 Impact of humic acid on grain protein and value cost ratio

(VCR) of maize crop ............................................................... ...12

2.2 Nitrogen .................................................................................. ...13

2.2.1 The importance of N nutrient .................................................. ...13

2.2.2 Nitrogen and physio chemical properties of soil .................... ...14

2.2.3 Soil organic matter and N availability .................................... ...14

2.2.4 Nitrogen and crop growth ....................................................... ...15

2.2.5 Nitrogen and maize physiological growth indices .................. ...17

2.2.6 Nitrogen and maize phenology ............................................... ...17

2.2.7 Nitrogen and maize grain yield ............................................... ...18

2.2.8 Impact of nitrogen on NUE (nitrogen use efficiency) of

maize ....................................................................................... ...20

2.2.9 Nitrogen and maize quality. .................................................... ...21

2.2.10 Effect of nitrogen on value cost ratio (VCR) of maize ........... ...22

2.2.11 The effect of humic acid and nitrogen on growth, yield and

quality of maize....................................................................... ...23

2.3 Maize genotypes ................................................................................. ...23

2.3.1 Maize genotypes and nitrogen ................................................ ...24

2.3.2 Maize genotypes and NUE ..................................................... ...25

2.3.3 The impact of maize genotypes on the growth and yield traits

of maize ................................................................................... ...25

2.3.4 Maize genotypes and humic acid ............................................ ...27

3. MATERIALS AND METHODS ................................................................. ...28

3.1 Experimental site ................................................................................ ...28

3.2 Pre-experimental soil analysis ............................................................ ...30

3.3 Experimental design, factors and treatments combination ................. ...31

3.4 The effects of the integration of humic acid with nitrogen on plant

development and phenology of maize genotypes ............................... ...33


growth of maize genotypes ................................................................. ...33

3.6 The effects of the integration of humic acid with nitrogen on leaf

growth and development of maize genotypes ..................................... ...33

3.7 The effects of the integration of humic acid with nitrogen on yield and

yield related attributes of maize genotypes ......................................... ...34

3.8 The effects of the integration of humic acid with nitrogen on soil

properties............................................................................................. ...34

3.9 Economic analysis of the integration of humic acid with nitrogen .... ...34

3.10 Meteorological Data............................................................................ ...35

3.11 Procedure for Data Recording ............................................................ ...35

3.11.1 The effects of the integration of humic acid with nitrogen on

plant development and phenology of maize genotypes .......... ...35


plant growth of maize genotypes ............................................ ...36


leaf growth and development of maize genotypes .................. ...36


yield and yield related attributes of maize genotypes ............. ...37


soil properties .......................................................................... ...41

3.11.6 Economic analysis of the integration of humic acid with

nitrogen ................................................................................... ...41

3.12 Data Analysis ...................................................................................... ...41

4. RESULTS ...................................................................................................... ...42



4.1.1 Days to emergence .................................................................. ...42

4.1.2 Days to 50% tasseling ............................................................. ...42

4.1.3 Days to 50% silking ................................................................ ...46

4.1.4 Anthesis to silking interval (ASI) ........................................... ...46

4.1.5 Days to maturity ...................................................................... ...50

4.1.6 Seed fill duration (SFD) .......................................................... ...50



4.2.1 Total weight plant-1 at silking ................................................. ...56

4.2.2 Ear weight plant-1 at silking .................................................... ...56

4.2.3 Plant height (cm) ..................................................................... ...62

4.2.4 Absolute growth rate (AGR) at silking ................................... ...65

4.2.5 Crop growth rate (CGR) at silking .......................................... ...65

4.2.6 Total weight plant-1 at maturity............................................... ...71

4.2.7 AGR at maturity ...................................................................... ...74

4.2.8 CGR at maturity ...................................................................... ...74



4.3.1 Leaves plant-1 at silking .......................................................... ...80

4.3.2 Leaf dry weight plant-1 at silking ............................................ ...80

4.3.3 Leaf area plant-1 at silking....................................................... ...86

4.3.4 Leaf area index (LAI) at silking .............................................. ...86

4.3.5 Specific leaf area (SLA) plant-1 at silking............................... ...92

4.3.6 Leaf area ratio (LAR) plant-1 at silking................................... ...92



4.4.1 Productive plants m-2 .............................................................. ...97

4.4.2 Ears plant-1 .............................................................................. ...101

4.4.3 Ears m-2 ................................................................................... ...101

4.4.4 Ear weight plant-1 at maturity ................................................. ...107

4.4.5 Ear length (cm) ....................................................................... ...111

4.4.6 Ear girth (cm) .......................................................................... ...111

4.4.7 Rows ear-1 ............................................................................... ...118

4.4.8 Grains row-1 ............................................................................ ...118

4.4.9 Grains ear-1 .............................................................................. ...124

4.4.10 1000 grain weight (g) .............................................................. ...124

4.4.11 Biological yield (kg ha-1) ........................................................ ...132

4.4.12 Grain yield (kg ha-1) ................................................................ ...132

4.4.13 Stover yield (kg ha-1) .............................................................. ...140

4.4.14 Harvest Index (%) ................................................................... ...140

4.4.15 NUE-AE (kg grains kg-1 N) .................................................... ...148

4.4.16 NUE-PFP (kg grains kg-1 N) ................................................... ...148

4.4.17 NAR (30-75 DAS) (g m-2 day-1) ............................................. ...156

4.4.18 Grain protein (%) .................................................................... ...156


properties............................................................................................. ...164

4.5.1 Soil phosphorous content (mg kg-1) at maize harvest ............. ...164

4.5.2 Soil nitrogen content (%) at maize harvest ............................. ...164

4.5.3 Soil organic matter (%) at maize harvest ................................ ...168


5. DISCUSSION ................................................................................................ ...174










properties............................................................................................. ...189


5.7 Genotypes×humic acid×nitrogen levels .............................................. ...192

6. SUMMARY, CONCLUSION AND RECOMMENDATIONS ................ ...196

7. REFERENCES ............................................................................................. ...203

8. APPENDICES .............................................................................................. ...249

i

LIST OF ABBREVIATIONS

G Genotypes

HA Humic acid

OPVs Open pollinated varieties

N Nitrogen

P Phosphorous

K Potassium

SFD Seed fill duration

AGR Absolute growth rate

CGR Crop growth rate

LA Leaf area

LAI Leaf area index

SLA Specific leaf area

LAR Leaf area ratio

TDM Total dry matter

LAD Leaf area duration

EC Electrical conductivity

OM Organic matter

DAS Days after sowing

LPP Leaves per plant

NUE Nitrogen use efficiency

NUE-AE Agronomic-nitrogen use efficiency

NUE-PFP Partial factor productivity- nitrogen use efficiency

ASI Anthesis to silking interval

BY Biological yield

GY Grain yield

SY Stover yield

HI Harvest index

AB-DTPA Ammonium bicarbonate-diethylene triamine pentaacetic acid

OM Organic matter

VCR Value cost ratio

NI Net income

R.H Relative humidity

ii

LIST OF TABLES

TABLE NO. TITLE PAGE NO.

1. Average air temperature (oC) and rainfall (mm) at ARS, Swabi during the year

2014 and 2015 ...........................................................................................................28

2. The physico-chemical properties (basic characteristics) of the composite soil

sample .......................................................................................................................30

3. The effect of humic acid and nitrogen on days to emergence of maize

genotypes ..................................................................................................................43

4. The effect of humic acid and nitrogen on days to 50% tasseling of maize

genotypes ..................................................................................................................44

5. The effect of humic acid and nitrogen on days to 50% silking of maize

genotypes ..................................................................................................................47

6. The effect of humic acid and nitrogen on anthesis to silking interval (ASI) of

maize genotypes ........................................................................................................48

7. The effect of humic acid and nitrogen on days to physiological maturity of

maize genotypes ........................................................................................................52

8. The effect of humic acid and nitrogen on seed fill duration (SFD) of maize

genotypes ..................................................................................................................54

9. The effect of humic acid and nitrogen on total weight (g) plant-1 at silking

stage of maize genotypes ..........................................................................................58

10. The effect of humic acid and nitrogen on ear weight (g) plant-1 at silking


11. The effect of humic acid and nitrogen on plant height (cm) of maize

genotypes ..................................................................................................................63

12. The effect of humic acid and nitrogen on AGR (g plant-1 day-1) of maize

genotypes ..................................................................................................................67

13. The effect of humic acid and nitrogen on CGR (g m-2 day-1) of maize

genotypes ..................................................................................................................69

14. The effect of humic acid and nitrogen on total weight (g) plant-1 of maize

genotypes at maturity ................................................................................................72

15. The effect of humic acid and nitrogen on AGR (g plant-1 day-1) of maize


iii

16. The effect of humic acid and nitrogen on CGR (g m-2 day-1) of maize


17. The effect of humic acid and nitrogen on leaves plant-1 at silking stage

of maize genotypes ...................................................................................................82

18. The effect of humic acid and nitrogen on leaf dry weight (g) plant-1 at silking


19. The effect of humic acid and nitrogen on leaf area (cm2) plant-1 at silking


20. The effect of humic aicd and nitrogen on leaf area index (LAI) of maize

genotypes at silking...................................................................................................89

21. The effect of humic acid and nitrogen on specific leaf area (cm2 g-1) plant-1

of maize genotypes at silking ....................................................................................93

22. The effect of humic acid and nitrogen on leaf area ratio (cm2 g-1) plant-1

of maize genotypes at silking ....................................................................................95

23. The effect of humic acid and nitrogen on productive plants m-2 of maize

genotypes ..................................................................................................................98

24. The effect of humic acid and nitrogen on ears plant-1 of maize genotypes ............103

25. The effect of humic aicd and nitrogen on ears m-2 of maize genotypes .................105

26. The effect of humic acid and nitrogen on ear weight (g) plant-1 of maize

genotypes at maturity ..............................................................................................108

27. The effect of humic acid and nitrogen on ear length (cm) of maize genotypes ......113

28. The effect of humic acid and nitrogen on ear girth (cm) of maize genotypes ........114

29. The effect of humic acid and nitrogen on rows ear-1 of maize genotypes. .............120

30. The effect of humic acid and nitrogen on grains row-1 of maize genotypes. ..........121

31. The effect of humic acid and nitrogen on grains ear-1 of maize genotypes ............126

32. The effect of humic acid and nitrogen on thousand grain weight (g)

of maize genotypes .................................................................................................127

33. The effect of humic acid and nitrogen on biological yield (kg ha-1) of maize

genotypes ................................................................................................................134

34. The effect of humic acid and nitrogen on grain yield (kg ha-1) of maize

genotypes ................................................................................................................135

iv

35. The effect of humic acid and nitrogen on stover yield (kg ha-1) of maize

genotypes ................................................................................................................142

36. The effect of humic acid and nitrogen on harvest index (%) of maize

genotypes ................................................................................................................143

37. The effect of humic acid and nitrogen on NUE-AE (kg grains kg-1 N)


38. The effect of humic acid and nitrogen on NUE-PFP (kg grains kg-1 N)


39. The effect of humic acid and nitrogen on net assimilation rate (g m-2 day-1)


40. The effect of humic acid and nitrogen on grain protein (%) of maize

genotypes ................................................................................................................159

41. The effect of maize genotypes, humic acid and nitrogen on P content (mg kg-1)

of soil at maize harvest ...........................................................................................165

42. The effect of maize genotypes, humic acid and nitrogen on N content (%)


43. The effect of maize genotypes, humic acid and nitrogen on organic matter (%)


44. Economic analysis of integration of humic acid with nitrogen in terms of US$

during 2014 and 2015. ............................................................................................171

45. Combined statistical analysis of variance for days to emergence of maize

genotypes as affected by humic acid and nitrogen ....................................................249

46. Combined statistical analysis of variance for days to 50% tasseling of

maize genotypes as affected by humic acid and nitrogen .......................................250

47. Combined statistical analysis of variance for days to 50% silking of maize


48. Combined statistical analysis of variance for ASI (anthesis to silking interval) of

maize genotypes as affected by humic acid and nitrogen .........................................252

49. Combined statistical analysis of variance for days to physiological maturity of


50. Combined statistical analysis of variance for seed fill duration (SFD) of maize


51. Combined statistical analysis of variance for total weight (g) plant-1 of maize

genotypes at silking as affected by humic acid and nitrogen ....................................255

v

52. Combined statistical analysis of variance for ear weight (g) plant-1 of maize

genotypes at silking as affected by humic acid and nitrogen. ...................................256

53. Combined statistical analysis of variance for plant height (cm) of maize


54. Combined statistical analysis of variance for AGR (g plant-1 day-1) of maize


55. Combined statistical analysis of variance for CGR (g m-2 day-1) of maize


56. Combined statistical analysis of variance for total weight (g) plant-1 of maize

genotypes at maturity as affected by humic acid and nitrogen ..................................260

57. Combined statistical analysis of variance for AGR (g plant-1 day-1) of maize


58. Combined statistical analysis of variance for CGR (g m-2 day-1) of maize


59. Combined statistical analysis of variance for leaves plant-1 at silking stages

of maize genotypes as affected by humic acid and nitrogen .....................................263

60. Combined statistical analysis of variance for leaf dry weight (g) plant-1

of maize genotypes as affected by humic acid and nitrogen ................................ ......264

61. Combined statistical analysis of variance for leaf area (cm2) plant-1 at silking

stages of maize genotypes as affected by humic acid and nitrogen ...........................265

62. Combined statistical analysis of variance for leaf area index (LAI) at silking

stages of maize genotypes as affected by humic acid and nitrogen ...........................266

63. Combined statistical analysis of variance for SLA (cm2 g-1) plant-1 of maize


64. Combined statistical analysis of variance for LAR (cm2 g-1) plant-1 of maize


65. Combined statistical analysis of variance for productive plants m-2 of maize


66. Combined statistical analysis of variance for ears plant-1 of maize genotypes as

affected by humic acid and nitrogen .........................................................................270

67. Combined statistical analysis of variance for ears m-2 of maize genotypes as


68. Combined statistical analysis of variance for ear weight (g) plant-1 of maize

vi


69. Combined statistical analysis of variance for ear length (cm) of maize


70. Combined statistical analysis of variance for ear girth (cm) of maize


71. Combined statistical analysis of variance for rows ear-1 of maize genotypes as


72. Combined statistical analysis of variance for grains row-1 of maize genotypes

as affected by humic acid, nitrogen and genotypes ................................................276

73. Combined statistical analysis of variance for grains ear-1 of maize genotypes as


74. Combined statistical analysis of variance for thousand grain weight (g) of


75. Combined statistical analysis of variance for biological yield (kg ha-1) of


76. Combined statistical analysis of variance for grain yield (kg ha-1) of maize


77. Combined statistical analysis of variance for stover yield (kg ha-1) of maize


78. Combined statistical analysis of variance for harvest index (%) of maize

genotypes as affected by humic acid and nitrogen. ...................................................282

79. Combined statistical analysis of variance for NUE-AE (kg grains kg-1 N) of


80. Combined statistical analysis of variance for NUE-PFP (kg grains kg-1 N) of


81. Combined statistical analysis of variance for NAR (g m-2 day-1) of maize

Genotypes as affected by humic acid and nitrogen ...................................................285

82. Combined statistical analysis of variance for soil P content (mg kg-1) at maize

harvest as affected by maize genotypes, humic acid and nitrogen ............................286

83. Combined statistical analysis of variance for soil N (%) at maize harvest as

affected by maize genotypes, humic acid and nitrogen .............................................287

84. Combined statistical analysis of variance for grain protein (%) of maize


vii

85. Combined statistical analysis of variance for soil organic matter (%) at maize

harvest as affected by maize genotypes, humic acid and nitrogen ............................289

viii

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

1. Average air temperature (oC) and rainfall (mm) at ARS, Swabi during the

year 2014. .............................................................................................................. .....29

2. Average air temperature (oC) and rainfall (mm) at ARS, Swabi during the

year 2015. .............................................................................................................. .....29

3. Interaction between N×HA for days to 50% tasseling of maize .......................... .....45

4. Interaction between N×G for days to 50% tasseling of maize. ................................45

5. Interaction between N×HA for days to 50% silking of maize. ................................49

6. Interaction between N×G for days to 50% silking of maize. ....................................49

7. Interaction between N×HA for days difference (ASI) of maize. .............................49

8. Interaction between N×HA for days to physiological maturity of maize .................53

9. Interaction between N×G for days to physiological maturity of maize. ...................53

10. Interaction between HA×G for days to physiological maturity of maize. ................53

11. Interaction between N×HA for seed fill duration (SFD) of maize. ..........................55

12. Interaction between N×G for seed fill duration (SFD) of maize. ............................55

13. Interaction between HA×G for seed fill duration (SFD) of maize ..........................55

14. Interaction between N×HA for total weight (g) plant-1 of maize at silking. .............60

15. Interaction between N×G for total weight (g) plant-1 of maize at silking. ................60

16. Interaction between HA×G for total weight (g) plant-1 of maize at silking. .............61

17. Interaction between N×G for ear weight (g) plant-1 of maize at silking. ..................61

18. Interaction between N×G for plant height (cm) of maize at maturity. .....................64

19. Interaction between HA×G for plant height (cm) of maize at maturity. ..................64

20. Interaction between N×HA for AGR (g plant-1 day-1) of maize at silking. ..............68

21. Interaction between N×G for AGR (g plant-1 day-1) of maize at silking. .................68

22. Interaction between HA×G for AGR (g plant-1 day-1) of maize at silking. ..............68

23. Interaction between N×HA for CGR (g m-2 day-1) of maize at silking. ...................70

ix

24. Interaction between N×G for CGR (g m-2 day-1) of maize at silking. ......................70

25. Interaction between HA×G for CGR (g m-2 day-1) of maize at silking. ...................70

26. Interaction between N×HA for total weight (g) plant-1 of maize at maturity. ..........73

27. Interaction between N×G for total weight (g) plant-1 of maize at maturity. .............73

28. Interaction between HA×G for total weight (g) plant-1 of maize at maturity. ..........73

29. Interaction between N×HA for AGR (g plant-1 day-1) of maize at maturity. ............77

30. Interaction between N×G for AGR (g plant-1 day-1) of maize at maturity. ...............77

31. Interaction between N×HA for CGR (g m-2 day-1) of maize at maturity. .................79

32. Interaction between N×G for CGR (g m-2 day-1) of maize at maturity. ....................79

33. Interaction between N×HA for leaves plant-1 of maize. ...........................................84

34. Interaction between N×G for leaves plant-1 of maize. ..............................................84

35. Interaction between HA×G for leaves plant-1 of maize. ...........................................85

36. Interaction between N×G for leaf dry weight (g) plant-1 at silking. .........................85

37. Interaction between N×G for leaf area (cm2) plant-1 of maize at silking. .................90

38. Interaction between N×HA for LAI of maize at silking. ..........................................90

39. Interaction between N×G for LAI of maize at silking. .............................................90

40. Interaction between HA×G for LAI of maize at silking. ..........................................91

41. Interaction between G×HA×N for LAI of maize at silking. .....................................91

42. Interaction between N×G for SLA (cm2 g-1) plant-1 of maize at silking. ..................94

43. Interaction between HA×G for SLA (cm2 g-1) plant-1 of maize at silking. ...............94

44. Interaction between N×HA for LAR (cm2 g-1) plant-1 of maize at silking. ..............96

45. Interaction between HA×G for LAR (cm2 g-1) plant-1 of maize at silking. ..............96

46. Interaction between N×HA for productive plants m-2 of maize. ..............................99

47. Interaction between N×G for productive plants m-2 of maize. .................................99

48. Interaction between HA×G for productive plants m-2 of maize. ..............................99

x

49. Interaction between G×HA×N for productive plants m-2 of maize. .......................100

50. Interaction between N×HA for ears plant-1 of maize. .............................................104

51. Interaction between N×G for ears plant-1 of maize. ................................................104

52. Interaction between HA×G for ears plant-1 of maize. .............................................104

53. Interaction between N×HA for ears m-2 of maize. ..................................................106

54. Interaction between N×G for ears m-2 of maize......................................................106

55. Interaction between HA×G for ears m-2 of maize ...................................................106

56. Interaction between N×HA for ear weight (g) plant-1 of maize at maturity. ..........109

57. Interaction between N×G for ear weight (g) plant-1 of maize at maturity...............109

58. Interaction between HA×G for ear weight (g) plant-1 of maize at maturity. ..........109

59. Interaction between G×HA×N for ear weight (g) plant-1 of maize at maturity. .....110

60. Interaction between N×HA for ear length (cm) of maize. ......................................115

61. Interaction between N×G for ear length (cm) of maize. .........................................115

62. Interaction between HA×G for ear length (cm) of maize. ......................................115

63. Interaction between N×HA for ear girth (cm) of maize. ........................................116

64. Interaction between N×G for ear girth (cm) of maize. ...........................................116

65. Interaction between HA×G for ear girth (cm) of maize. ........................................116

66. Interaction between G×HA×N for ear girth (cm) of maize. ...................................117

67. Interaction between N×HA for grain rows ear-1 of maize. .....................................122

68. Interaction between N×G for grain rows ear-1 of maize. ........................................122

69. Interaction between N×HA for grains row-1 of maize ............................................123

70. Interaction between N×G for grains row-1 of maize ...............................................123

71. Interaction between HA×G for grains row-1 of maize ............................................123

72. Interaction between N×HA for grains ear-1 of maize..............................................128

73. Interaction between N×G for grains ear-1 of maize. ...............................................128

xi

74. Interaction between HA×G for grains ear-1 of maize..............................................128

75. Interaction between G×HA×N for grains ear-1 of maize. .......................................129

76. Interaction between N×HA for 1000 grain weight (g) of maize .............................130

77. Interaction between N×G for 1000 grain weight (g) of maize................................130

78. Interaction between HA×G for 1000 grain weight (g) of maize .............................130

79. Interaction between G×HA×N for 1000 grain weight (g) of maize........................131

80. Interaction between N×HA for biological yield (kg ha-1) of maize ........................136

81. Interaction between N×G for biological yield (kg ha-1) of maize ...........................136

82. Interaction between HA×G for biological yield (kg ha-1) of maize ........................136

83. Interaction between G×HA×N for biological yield (kg ha-1) of maize ...................137

84. Interaction between N×HA for grain yield (kg ha-1) of maize................................138

85. Interaction between N×G for grain yield (kg ha-1) of maize. .................................138

86. Interaction between HA×G for grain yield (kg ha-1) of maize................................138

87. Interaction between G×HA×N for grain yield (kg ha-1) of maize. .........................139

88. Interaction between N×HA for stover yield (kg ha-1) of maize ..............................144

89. Interaction between N×G for stover yield (kg ha-1) of maize .................................144

90. Interaction between HA×G for stover yield (kg ha-1) of maize ..............................144

91. Interaction between G×HA×N for stover yield (kg ha-1) of maize .........................145

92. Interaction between N×HA for harvest index (%) of maize ...................................146

93. Interaction between N×G for harvest index (%) of maize ......................................146

94. Interaction between HA×G for harvest index (%) of maize ...................................146

95. Interaction between G×HA×N for harvest index (%) of maize ..............................147

96. Interaction between N×HA for NUE-AE (kg grains kg-1 N) of maize ...................152

97. Interaction between N×G for NUE-AE (kg grains kg-1 N) of maize ......................152

98. Interaction between HA×G for NUE-AE (kg grains kg-1 N) of maize ...................152

xii

99. Interaction between G×HA×N for NUE-AE (kg grains kg-1 N) of maize ..............153

100. Interaction between N×HA for NUE-PFP (kg grains kg-1 N) of maize ..................154

101. Interaction between N×G for NUE-PFP (kg grains kg-1 N) of maize.....................154

102. Interaction between HA×G for NUE-PFP (kg grains kg-1 N) of maize. .................154

103. Interaction between G×HA×N for NUE-PFP (kg grains kg-1 N) of maize ............155

104. Interaction between N×HA for NAR (30-75 DAS) (g m-2 day-1) of maize ............160

105. Interaction between N×G for NAR (30-75 DAS) (g m-2 day-1) of maize ...............160

106. Interaction between HA×G for NAR (30-75 DAS) (g m-2 day-1) of maize ............160

107. Interaction between G×HA×N for NAR (30-75 DAS) (g m-2 day-1) of maize .......161

108. Interaction between N×HA for grain protein content (%) of maize .......................162

109. Interaction between N×G for grain protein content (%) of maize ..........................162

110. Interaction between HA×G for grain protein content (%) of maize .......................163

111. Interaction between G×HA×N for grain protein content (%) of maize ..................163

112. Interaction between N×HA for soil P content (mg kg-1) at maize harvest..............167

113. Interaction between HA×G for soil N content (%) at maize harvest. .....................167

114. Interaction between N×HA for soil organic matter (%) of maize. .........................170

115. Interaction between HA×G for soil organic matter (%) of maize. .........................170

xiii

ACKNOWLEDGEMENTS

I am extremely thankful to almighty ALLAH, The beneficent and merciful who helped

me a lot in every moment of my life. I offer my humblest thanks to The Holy Prophet “Hazrat

Mohammad (SAW)”, who is forever a source of guidance and inspiration for humanity.

I would like to express my deep gratitude to my worthy and honorable advisor Prof. Dr.

Sami Ullah Khan, Department of Agronomy, The University of Haripur, for giving me an

opportunity to work under his dynamic supervision. His indispensable guidance and valuable

support had provided me a good basis for my report and research work.

I am thankful to the Chairman department of Agricultural Sciences, Prof. Dr. Ayub Khan,

Dr. Ali Raza Gurmani, Dr. Shah Masaud Khan and all the faculty members of the department, the

University of Haripur, for their support and moral help.

I am also thankful to my seniors, friends and my colleagues Dr. Muhammad Arif, Dr. Fazal

Munsif, Dr. Khalid Ali and my cousin Riaz Ali, PST teacher, for their valuable guidance and

support in writing this thesis.

Last but not least, I am thankful to my dear mother, brothers, sisters and all my family

members for their continuous encouragement and unreserved love throughout my study.

Shad Ali Khan

xiv

Integration of humic acid with nitrogen for improving yield of maize

genotypes

Shad Ali Khan and Dr. Sami Ullah Khan,

Department of Agricultural Sciences (Agronomy)

University of Haripur, Khyber Pakhtunkhwa, Pakistan

ABSTRACT

Soil, being an important constituent of crop production, serves as a major source of

plant nutrients availability as well as metabolic processes which are indispensible for plant

growth, development and survival. The integration of humic acid and inorganic fertilizers may

help to fight the deficiency of essential nutrients and improve the soil fertility for better crop

yield. Bearing in mind the above objectives, the current study was carried out at the

Agricultural Research Station, Swabi for two consecutive years of 2014 and 2015. The

experiment was carried out in randomized complete block (RCB) design using split-split plot

arrangement and three replications. Four maize genotypes (3025, 55w65, Jalal and Iqbal), four

N levels (0, 120, 180 and 240 kg N ha-1) and four treatments of humic acid (0, 0.6, 1.2 and 1.6

kg HA ha-1) were included in it. Regarding maize genotypes, late emergence, maximum days

to 50% tasseling, 50% silking, anthesis to silking interval (ASI), days to physiological maturity,

seed fill duration (SFD), leaves plant-1, leaf dry weight plant-1 at silking, leaf area plant-1 at

silking, leaf area index (LAI) at silking, absolute growth rate (AGR) and crop growth rate

(CGR) at silking, plant biomass, plant height, yield and yield components, harvest index (HI),

agronomic-nitrogen use efficiency (NUE-AE), partial factor productivity-nitrogen use

efficiency (NUE-PFP) and net income (NI) were recorded for hybrid 55w65, while higher AGR

as well as CGR at maturity and productive plants m-2 were calculated for hybrid 3025.

However, maximum specific leaf area (SLA) plant-1, leaf area ratio (LAR) plant-1, net

assimilation rate (NAR) (30-75 DAS), soil attributes (organic matter, P and N) at maize harvest

and grain protein were observed for Iqbal variety.

As far as humic acid (HA) treatments are concerned, maximum days to physiological

maturity, SFD, leaves plant-1, leaf dry weight plant-1 at silking, leaf area plant-1, LAI, AGR,

CGR at silking, plant biomass, plant height, AGR, CGR at maturity, productive plants m-2,

yield and yield components were recorded at 1.8 kg HA ha-1. Furthermore, humic acid at 1.8

kg ha-1 provided higher grain yield, biological yield, harvest index, NUE-AE, NUE-PFP, NAR

(30-75 DAS), soil attributes at maize harvest, grain protein and net income, while it resulted in

lower SLA and LAR plant-1 at silking. Similarly, 1.8 kg HA ha-1 had earlier 50% tasseling and

50% silking, whereas higher SLA and LAR plant-1 were recorded for control plots of humic

xv

acid (0 kg HA ha-1).

While considering the impact of nitrogen levels, delayed physiological maturity, SFD,

higher number of leaves plant-1, leaf dry weight plant-1, leaf area plant-1, LAI, AGR, CGR at

silking, plant biomass, plant height, AGR, CGR at maturity, productive plants m-2, yield and

yield components, harvest index, NAR (30-75 DAS), soil attributes at maize harvest, grain

protein and net income were observed at 240 kg ha-1 N, while it resulted in lower SLA and

LAR plant-1 at silking. Similarly, 240 kg ha-1 N application induced earliness in days to 50%

tasseling, 50% silking and shortened the ASI. Likewise, higher SLA and LAR plant-1 at silking

were calculated at 0 kg ha-1 N. Moreover, higher NUE-AE was achieved at 180 kg ha-1 N while

NUE-PFP was higher under 120 kg N ha-1.

The integration of humic acid with nitrogen increased the number of days taken by the

maize genotypes to attain their physiological maturity, SFD, the number of leaves plant-1, leaf

dry weight plant-1, leaf area plant-1, leaf area index, AGR, CGR at silking, plant biomass, plant

height, AGR, CGR at maturity, productive plants m-2, yield and yield components, harvest

index, NAR (30-75 DAS), soil attributes at maize harvest, grain protein and net income.

Moreover, the number of days to emergence, 50% tasseling, 50% silking and ASI were also

reduced when the inorganic fertilizer of N was supplemented by humic acid in maize

genotypes, with subsequent improvement in their NUE-AE, NUE-PFP. However, the SLA and

LAR of maize genotypes exhibited a downward trend with the application of humic acid + N.

Thus it is finally concluded that 240 kg N ha-1 + 1.8 kg HA ha-1 along with hybrid maize 55w65

may be used for obtaining higher grain yield and improving soil organic matter status under

the agro-climatic conditions of Swabi region on sustainable basis.

1

I. INTRODUCTION

Maize occupies an important position in the cereal crops (Rahmati, 2012) and

is considered as the mainstay of our livelihood because it provides staple food to a large

portion of the human population (Farhad et al., 2009). It is a main source of income for

resource poor farmers in the country (Tagne et al., 2008) because it gives the highest

yield among cereal crops in the world (Jack, 2010). The increase in food production for

withstanding famine and poverty of an ever increasing population of our region is a

matter of grave concern for agricultural scientists. The lower yield of food crops proves

a great obstacle in the way of achieving sustainable and long lasting food security (Ali

et al., 2011). Thereupon, looking out methods of increasing cereal crops production

without impairing and deteriorating soil health is our main objective (Delate and

Camberdella, 2004).

Maize was selected as a trial crop as it is a prominent short duration (Farhad et

al., 2009) food and feed crop of the world (Tahir et al., 2008) and is proficient in

utilization of nutrients with better yield potential (Govt. of Pakistan, 2009). In Pakistan,

maize crop is sown on large area after wheat and rice, with 98% of its area in Punjab

and Khyber Pakhtunkhwa. It is intensely grown on worldwide basis and is called as

“king of grain crops” (Tahir et al., 2008). In Pakistan, maize occupies 1117 thousand

ha area, producing 2527 thousand tons of grain annually with average grain yield of

about 4053 kg ha-1 (Pakistan Economic Survey, 2014). Within the prevailing farming

practices, the soil natural indigent fertility level as well as burgeoning prices of

inorganic (synthetic) fertilizers is creating an alarming challenge to yield potential of

maize crop (Shah and Khan, 2003). The necessity to concurrently enhance yield, lower

the cost of production, and keep the soil in a healthy position is the primary issue and

question for agricultural scientists presently (Anjum et al., 2011).

Nitrogen plays a vital role in crop growth (Ahmad, 2000) and its scarcity is

counted as the main yield retarding factor in addition to the other components which

negatively affect maize crop production (Shah et al., 2003) because it is a nitropositive

crop (Gökmen et al., 2001). Nevertheless, decrease in nitrogen use efficiency and

increase in water pollution below the soil surface as a result of NO3 leaching possibly

is the outcome of repeated applications of mineral (inorganic) N (Guo et al., 2006; Ju

et al., 2007). Furthermore, insufficient and poor nutrient management has depleted

2

nutritional status of the soil with the course of time which reduces the yield of crops as

well as fertility of the soil (Afzal and Ahmad, 2009).

Regarding the diversity in soil types, cropping patterns and sources of crop

production, several management practices may be exercised to diminish and minify the

extent of soil fertility deterioration. In spite of various soil types, cropping patterns,

crop seasons and organic amendments; the use of humic acid is more useful and

economical, in comparison to synthetic fertilizers in enhancing soil C and organic

matter content (Dong et al., 2006). Humic acid contains phenolic, amino, quinone and

acidic groups that aid in the provision of nutrients in those soils which are deficient in

organic matter (Sadiq et al., 2014). It is soluble in water because of carboxyl, hydroxyl,

alkyl and phenolic groups (Mackowiak et al., 2001). As most Pakistani soils have so

far less than 1% of organic matters (Azam et al., 2001) so it is more productive in our

soil conditions. It contains 0.032% N (Kjeldahl), 0.89% P (spectrophotometer method),

2.12% K (flame photometer), 0.41 mg kg-1 Fe and 0.45 mg kg-1 Zn (atomic absorption

spectrophotometer), while its carbon content is 54% (Khan et al., 2014). It is believed

that humic acid increase crops yield due to its potential of increasing nitrogen (N) and

phosphorous (P) availability in the soil (Sajid et al., 2012). High production cost of

inorganic fertilizers, especially nitrogen and its inclination to various losses (leaching,

volatilization and denitrification) has induced peasants and farmers to use organic

sources of nutrients (Delate and Camberdell, 2004; Hammad et al., 2011). In addition

to high cost, the application of synthetic fertilizers to crops is also correlated with

enhanced soil degradation and heavy pollution of the environment (Oad et al., 2004;

Bhattacharyya et al., 2008). Humic acid improves root vigor, nutrient uptake,

chlorophyll content, seeds germination, stimulates bacterial activities, enhances crop

yield and particularly increases fertilizer retention when it is applied to the soil (Shazma

et al., 2016) due to its chelating nature (Madronová et al., 2001).

By evolving integrated and sustainable nutrient management farming practices

we can improve ecosystem (microorganisms and environment) as well as fertility status

of the soil (Liu et al., 2009). The use of humic substances like humic acid can increase

the efficiency of synthetic fertilizers (Billingham, 2012). It is studied that these

substances accelerate root growth of the crop and enhance fertilizer efficiency (Liang

et al., 2016). In addition to the supply of nutrients they prove to be a good reclamation

agent for the degraded and poorly managed soils (Sánchez-Monedero et al., 2004). The

3

nitrogen recovery of maize is improved by 58-63% with the application of organic

fertilizer (manure) in integration with mineral nitrogen (Nyamangara et al., 2003).

Humic acid being an organic-mineral fertilizer (Azarpour et al., 2012) and organically

charged biostimulant (Moghdam et al., 2015) promotes soil N as well as OM situation

which results in boosting up the crop yield. It performs a crucial role in accelerating

maize yield because it not merely provides major (macro) nutrients but at the same time

is a true source of minor (micro) nutrients also (Madronová et al., 2001). Synthesis of

protein, chlorophyll, DNA as well as many enzymatic activities may be promoted by

the micronutrients being made available (Reddy, 2004). For the purpose of acquiring

sustainability in production of crops, it is essential to build up equilibrium between

nutrients added to the soil and removed by the crops for their growth, development and

survival as well (Rijpma and Jahiruddin, 2004). Therefore, incorporation of humic acid

as an organically charged biostimulant deserves more consideration for accelerating

yield of various crops without impairing soil quality as 1 kg of humic acid can substitute

for 1000 kg of farm yard manure (Hammad et al., 2011; Tahir et al., 2011; Humintech,

2012).

Poor NUE (nutrient use efficiency) and rapid degradation of soil hinder crop

production and creates food security problems (Jones et al., 2012). It is a crucial need

of our ages to make up for the deficiencies found in the agro-ecosystem, like breakup

and discontinuity in the nutrients smooth flow, excessive demand by the crops, nutrients

recycling, and deficiency in water use efficiency (WUE) (Lal, 2013). One way of

solving the problem is the recycling of nutrients and organic compounds (wastes) back

to the root zone of soil which can aid in maintaining soil OM portion, enhance soil

biological activities, moisture retention, aeration, nutrient supply and can help in

reducing the soil compaction (Girmay et al., 2008). The potential types of organic

matter that may be incorporated in soil are varying in nature, ranging from industrial

wastes, animal wastes to household wastes, crop residues and green manures (Grant,

2002; Ali et al., 2011). The organic matter of soils can be divided into non-humic

(carbohydrates, amino acids, proteins, lipids, nucleic acids and lignins) and humic

substances (Xavier et al., 2012). Humic substances are produced through organic matter

decomposition and applied as soil conditioners for the purpose of improving soil

structure and density of microorganisms (Unlu et al., 2011). Humates have a special

stimulatory effect on the availability of plant nutrients. Application of these substances

4

can elevate growth, yield and quality in a number of plant species (Karakurt et al., 2009)

to a certain extent, through promotion of nutrient uptake, and by playing as a source

and regulator of mineral plant nutrients (Atiyeh et al., 2002).

Improving maize production is thought to be the utmost important strategy for

ensuring food security of our instantly growing population. However, synthetic

fertilizers and genetically improved maize genotypes, i.e. hybrids and open pollinated

varieties (OPVs) having superior selected traits i.e. high disease resistance, drought

tolerance, early maturity, increased yield per unit area, and quality protein (Byerlee et

al., 1994 ), are not yet adopted in Pakistan on a large scale. Cultivars are selected based

on adaptation to a number of weather climatic characteristics (elevation, rainfall,

temperature) and genetic factors (grain quality, yield, maturity and grazing potential).

No cultivar shows all the acceptable characteristics and selection is dependent on

comparing the different risk factors involved (Freebairn, 2005). Likewise, cultivars

have immense potential regarding their production, as yield may be improved by the

release of cultivars having superior inherent traits (Khalil et al., 2002a). It is very

important to identify those maize genotypes that are capable to produce high grain yield

under low management cropping systems as practiced by small land holder farmers, as

until now very little effort has been made in this regard (Tolessa et al., 2007). Research

results have shown that various maize hybrids are significantly different in grain yield

response to cultural practices (Ali et al., 2011). The varying response is primarily due

to differences in their physiological maturity (Farnham, 2001; Widdicombe et al.,

2002), plant morphology (Benga et al., 2001), SFD (Ying et al., 2000; Echarte et al.,

2006), competition among maize plants (Maddonni and Otegui, 2004; Maddonni and

Otegui, 2006), CGR (Echarte et al., 2000), density stress tolerance (Tollenaar and Wu,

1999; Tollenaar and Lee, 2002), sink capacity (Borras and Westgate, 2006; Gambín et

al., 2006), profile of vertical leaf area, and uptake as well as utilization of N (Valentinuz

and Tollenaar, 2006). Yield advancement in last 50 years is due to inbreeding and

improved cultural practices in which nitrogen played a crucial role (Duvick, 1992;

Sinclair and Muchow, 1995).

Keeping in view the importance of humic acid and nitrogen, the present study

was conducted with the aim to find out the appropriate nitrogen levels for higher maize

productivity and improved soil physico-chemical properties for both maize hybrids and

OPVs (open pollinated varieties) in integration with humic acid.

5

OBJECTIVES

The current research study was conducted to fulfill the following objectives.

1. The quantification of optimum humic acid level for enhancing maize yield and

accelerating soil fertility level on sustainable basis.

2. The estimation of optimum nitrogen level for maize genotypes having increased

yield per unit area.

3. Assessment of the integrated effect of humic acid and nitrogen for improving yield

and economic returns of maize genotypes.

4. Evaluation of the maize genotypes having better yield per unit area with higher

nitrogen use efficiency.

6

2. REVIEW OF LITERATURE

In this chapter we have focused on the role of humic acid and nitrogen

fertilization on yield and yield components of maize crop along with soil physical and

chemical properties in view of the previous findings and results.

2.1 Humic Acid

2.1.1 The importance of humic acid

Humic acid acts as an organically charged bio-stimulant (Moghadam et al.,

2015) and is the primary source of soil organic matter (OM) (Chen and Aviad, 1990).

It improves the physical (Varanini et al., 1995), chemical and biological properties of

soil (Khattak, 2004) with acceleration in agro-environmental performance of the farms

(Popescu and Popescu, 2018). It is formed as a by-product through the process of

humification of organic materials by soil microorganisms (Abakumov et al., 2018) and

can also be prepared in the laboratory from plant residues with the help of chemicals

(Khan et al., 2013). Furthermore, it serves as a store house for plant macro nutrients

like nitrogen, phosphorous and potassium (Gatabazi, 2014) and micro nutrients in the

form of chelates (Madronová et al., 2001). However, the amount of organic matter and

essential nutrients is very low in the cultivated soils of Pakistan (Rashid and Ahmad,

1994; Jilani et al., 2007). Therefore, the use of humic acid is very helpful in increasing

per acre crop production because it has the potential of enhancing soil fertility status

(Khan et al., 2014). Likewise, humic acid have a significant impact on mineral

nutrition, germination of seed, root initiation, seedling growth and plant development

(Celik et al., 2011; Tahir et al., 2011) and thus enhances the uptake of nutrients (Tan,

2003).

The humic acid being the principal component of soil organic matter activates

plants harmonic/enzymatic system, improves crop yield (Bakry et al., 2009) and soil

fertility in an ecologically friendly way (Sarir et al., 2005). It acts as a slow release

fertilizer of N because the nitrogen available in it is in a very stable form (Nisar and

Mir, 1989). The positive role of humic acid is well accepted in suppressing soil born

diseases, maintaining soil health, nutrients availability, their uptake and crop quality

(Mauromicale et al., 2011). It accelerates crop growth, increases water holding capacity

of soils, helps in reduction of soil salinity (Kim et al., 2012) and enhances the retention

of fertilizers in the soil (Shazma et al., 2016). Due to the complexation and basal

7

exchange capacities of humic acid, its use is important in the stability of soil,

transportation of nutrients to plants organs, stability of soil OM and in assimilation of

plants nutrients (Fahramand et al., 2014). The dose of humic acid used as a fertilizer in

the field is generally very low i.e. 1-2 kg ha-1, which may supply only 0.001 kg P and

0.04-0.08 kg N ha-1 to the soil (Brannon and Sommers, 1986) but it is still important as

its ingredients (C, N and P) accelerates the supply of nitrogen and phosphorous to the

crop and increases its yield (Sajid et al., 2012).

2.1.2 Humic acid and soil physio chemical properties

Humic acid is used as a complement with synthetic fertilizers (Sajid et al., 2012)

as it is an effective chelating agent (Madronová et al., 2001) and a source of soil organic

matter (Chen and Aviad, 1990) which enhances soil fertility and its production capacity

(Azeem et al., 2014). The soil organic matter improves physio-chemical properties of

the soil like its pH, aeration, permeability, aggregation, ions transport and availability

(Selim et al., 2010). Its sufficiency in the soil is considered to be of practical importance

as it reduces the requirement of chemical fertilizers and enables the plants and soil

ecosystem to work in a better way (Sajid et al., 2012) as it promotes nutrients retention

potential of soils (Ali et al., 2015). In most cases, application of humic acid could lead

towards sustainable agriculture through humus production and sustaining microbial

activities (Sajid et al., 2012). Therefore, the integration of humic acid and inorganic

fertilizer in a balanced manner can enhance the fertility of marginal soils having lower

organic matter especially in the arid and semi arid regions of the world where there is

scarcity and rapid decomposition of soil organic matter (Chen and Aviad, 1990; Khan

et al., 2012).

Soil application of humic acid (HA) increases soil organic carbon (SOC), soil

acidity and cation exchange capacity (CEC) (Hanafi and Salwa, 1998). It improves the

nutrients use efficiency of fertilizers by enhancing the availability and uptake of macro

and micro nutrients by the plants (Chen et al., 1999; Tahir et al., 2011). The increase in

microbial activities is considered to be responsible for enhanced nutrient uptake

(Mayhew, 2004) as humic acid is an organic fertilizer and the main C source of food

for soil microorganisms (Sarwar et al., 2012). In addition, the humic acid has a peculiar

role in the prevention of ground water pollution, nutrients leaching, improved soil

structure (Schofield et al., 2012; Nithila et al., 2013) and water use efficiency (WUE)

of the plants (Delfine et al., 2005; Morard et al., 2011). Likewise, HAs in the soil have

8

a direct effect on roots elongation, their respiration, cell membrane permeability,

oxygen (O2), N and P uptake (Nardi et al., 2002). Humic acid increases the performance

of enzyme phosphatase in the soil as it hydrolyses phosphate esters and releases the

inorganic P in available form (Malcolm and Vaughan, 1979). Humic acid attracts

micronutrients, by forming a chelate and then slowly releases them according to the

plant demand which is associated with increased crop yield (Yingei, 1988) as observed

by Khattak and Muhammad (2013) when they added HA to the soil at the rate of 2 kg

ha-1.

2.1.3 The effect of humic acid on N and P nutrients

Humic acid improves the nitrogen use efficiency (NUE) and reduces ground

water pollution by promoting the concentration of soil exchangeable ammonium

(NH4+) and available nitrate (NO3

-) which leads towards more nitrogen (N) retention in

the soil and its uptake by the plants (Mohd et al., 2009). As such, it boosts up the

activities of nitrifying bacteria in the soil (Vallini et al., 1997). Besides, it has a

significant role in the stabilization of P fertilizers in the soil (Day et al., 2000). It

prevents it from precipitation with soil Fe and Al through chelation (complextation)

reactions (Banfield and Hamers, 1997). Furthermore, the chelation of nutrients

increases their availability in soil solutions to be easily taken by the crops (Chen, et al.,

1999). Keeping in view the higher prices of fertilizers, fixation and absorption losses,

leaching, volatilization and limited use of chemical fertilizers, the use of humic acid

has gained much importance as a source of N and P for improving crop yield on

sustainable basis (Qadoons et al., 2015). Although it does not provide a significant

portion of inorganic nutrients (macro and micro) for plant growth but it is still important

as it can enhance their efficiency many times (Emad et al., 2012).

2.1.4 The role of humic acid in crop production

2.1.4.1 Humic acid and maize phenology

Humic acid can be used in the crop production as soil conditioner, plant growth

promoter and nutrient carrier (Nisar and Mir, 1989). It has special stimulatory effect on

nutrients availability, nutrient uptake and their transportation to the growing parts of

maize plants which results in higher growth (Celik et al., 2010). As reported, its

application decreased days to 50% tasseling and silking in maize crop at Ismaila and

Nubaria (El-Mekser et al., 2014) due to the acceleration in the processes of respiration

9

and metabolism during its life cycle (Fagbenro and Agboola, 1993). Upon enterance

into the plants organs through their roots (Nardi et al., 1996) humic susbstances (HSs)

affect various metabolic processes of the plants (Tan, 2003). They increase the rate of

respiration (Vaughan and Malcolm, 1985), stimulate plant nutrition (Varanini and

Pinton, 2001; Ghabbour et al., 2001), promote hormonal activities (Nardi et al., 2002),

enhance enzymatic reactions (Nardi et al., 2002) and provide energy for continuation

of different physiological activities (Zancani et al., 2009). Qadoons et al. (2015) found

out that days to tasseling, silking and maturity were significantly affected by humic acid

application in maize crop. They studied that 9 kg ha-1 humic acid reduced days to

tasseling and silking while it increased the time interval of maize crop to reach its

maturity stage. Similarly, Puglisi et al. (2009) reported that HA had special influence

on plant physiology, plant dry matter production, lateral roots initiation, cell respiration,

hormonal activities, and nutrients uptake by the plant cells. Furthermore, early tasseling

and reduced silking of maize plants resulted in shorter ASI (anthesis to silking interval)

(Kolari et al., 2014). Physiological maturity and seed fill duration of maize crop became

lengthy due to HA application because it is a slow release fertilizer of nutrients (Dahal

et al., 2014; Santa and Shrestha, 2014).

2.1.4.2 Humic acid and maize physiological growth indices

Humic acid being utilized as a cheap organic source of fertilizer promotes plant

growth, increases stress tolerance, improves the physical conditions of the soil and

make complexation with metallic ions (Atiyeh et al., 2002; Nardi et al., 2002;

Zandonadi et al., 2007). It is thought to accelerate the impact of NPK fertilizers on

plants growth (Pollhamer, 1993; Chen et al., 2004). Due to the chelating capcity of

humic acid, it has the potential to overcome the deficiency of different nutrients in the

soil. Furthermore, it enhances the crop growth, production and quality on account of its

hormonal like effects (Abdel-Mawgoud et al., 2007). Motaghi and Nejad (2014)

observed in a field study that when humic acid was used at the rate of 100 ppm, it

significantly increased total dry weight (TDW), leaf area index (LAI), crop growth rate

(CGR) and net assimilation rate (NAR) of cowpea. The N contained in humic acid

(Khan et al., 2010) promotes vegetative growth of the crop (Azeem et al., 2014)

especially in the semi arid environmental conditions (Khan et al., 2010) while the K

content of it increases plant photosynthesis, cell division, crop growth rate and water

reservation in the plant cells (Saber and Zanati, 1984). In a field study, Sharifi (2017)

10

evaluated the significant effect of HA on enhanced nutrients availability and increase

in leaf area index (LAI) of various crops. Increased nutrient uptake, stimulated

microbial activities (Mayhew, 2004), higher root initiation and root growth (Gomaa et

al., 2014) as a result of HA application is then considered responsible for vigorous

vegetative growth of the maize plants (Bakry et al., 2009). Azeem et al. (2014) attained

higher leaf area and crop growth rate in maize crop when it received HA at the rate of

4.5 kg ha-1. Likewise, Daur and Bakhashwain (2013) indicated the significant impact

of humic acid application on maize plant height, LAI and chlorophyll content.

2.1.4.3 Humic acid and maize yield

As humic acid is a mixture of various macro and micro elements, it raises the

fertility of soil, nutrients availability, crop growth and yield (Moraditochaee, 2012).

Therefore, it is used mainly in marginal alkaline and poor calcareous soils to improve

nutritional status of the soil and crop production (Rajpar et al., 2011). It has substantial

impact on the growth of higher plants (Ashraf et al., 2005; Susilawati et al., 2009),

lowers the losses of fertilizes, minimizes the use of chemical fertilizers and reduces the

cost of crop production as it provides a conducive environment for its root growth (El-

Akabawy, 2000). That is why, Azeem et al. (2014) suggested in a field study that

addition of humic acid to the maize crop at the level of 3 kg ha-1 increased emergence

m-2, produced maximum grains per ear, higher economic yield and 1000 grain weight.

Likewise, Qadoons et al. (2015) reported a significant improvement in number of grains

ear-1, 1000 grain weight, biological yield and economic yield due to humic acid

application (9 kg ha-1) in his experiment as compared to control. In a similar study,

Ghorbani et al. (2010) studied that humic acid amendment at the rate of 3.5 kg ha-1

provided significantly higher grain yield, biological yield, dry matter accumulation, leaf

area index, leaf area duration, plant height, row number and ear length of maize crop.

Furthermore, Mohana et al. (2015) obtained higher leaf area index (LAI), leaves plant-

1, plant height, cob length, cob height, grains ear-1, shelling percentage (%), thousand

(1000) grain weight and grain yield as a consequence of humic acid application in his

field trial.

Bakry et al. (2009) reported higher ear length, ear diameter, rows ear-1, grains

ear-1, grain yield and 1000 grain weight in his experiment due to the application of

humic acid. Likewise, Daur and Bakhashwain (2013) observed the increased number

of leaves plant-1, larger leaf area (LA), taller plant height, higher grain protein

11

concentration and grain yield over control due to humic acid incorporation. It improves

the soil structure with enhanced uptake of N, P, K (macro nutrients), and Fe, Zn, Cu,

Mn (micro nutrients) which finally results in better growth and yield characteristics of

maize crop (Chen et al., 1999). Similarly, Gomaa et al. (2014) found that ear length,

rows ear-1, grains row-1, grains ear-1, 1000 grain weight, stover yield, grain yield,

biological yield and harvest index (%) of maize hybrids increased significantly with

humic acid amendments. According to López-Bellido and López-Bellido (2001), grain

yield has a positive correlation with 1000 grain weight. Sharif et al. (2003) reported

that humic acid application at the rate of 1 kg ha-1 enhanced the grain yield of maize,

wheat, cotton, sugar beet and groundnut crops up to 20% along with improvement in

physio chemical properties of the soil. They also observed an increase of 25% in the

biological yield of maize as a consequence of humic acid application in comparison to

control plots (Sharif et al., 2004). In the same way, Khan et al. (2014) got an increase

of 29% and 42% in ear weight, and 11.5% and 29% in grain weight ear-1 of maize over

control when they used humic acid at the rate of 25 and 50 mg kg-1 soil respectively.

Moreover, the harvest index of maize crop also increases as a result of HA application

because there is a significant relationship between seed yield and harvest index of cereal

crops (Singh and Saxena, 1990).

2.1.4.4 Humic acid and maize quality

Humic acid being rich in organic matter enhances the water uptake, dry matter,

mineral composition and grain protein concentration of maize crop (Delfine et al.,

2005; Morard et al., 2009). It helps in the mitigation of soil salinity and accelerates the

uptake of nitrogen, phosphorous, potassium, calcium, magnesium, iron, copper, zinc

and manganese by the maize plants (Daur and Bakhashwain, 2013). Furthermore, Nardi

et al. (2002) concluded from a field study that humic acid application brought various

biochemical changes in the cell wall, cell membrane and cytoplasm of plants with

acceleration in photosynthesis, respiration, hormonal activities and grain protein

content (%). The reason is that humic acid forms complex chelates with micro nutrients

which can enter easily in the plant cells as compared to common ions (Rassam et al.,

2015). Likewise, Majidian et al. (2006) reported that the integration of humic acid with

inorganic fertilizers, led towards better soil conditions, corn quality, higher yield,

minimum use of chemical fertilizers and paved the way for the development of

sustainable agriculture. Similarly, El-Mekser et al. (2014) observed the significant

12

effect of foliar application of humic acid on protein, fat, minerals and amylase content

of maize crop in a field experiment conducted at Ismaila and Nubaria. They also

reported an increase in the micro nutrients (Fe, Zn and Mn) contents of crop as a result

of humic acid application because it has a critical role in the synthesis of DNA

(deoxyribonucleic acid), RNA (ribonucleic acid) and various biochemical reactions.

2.1.4.5 Humic acid and nitrogen use efficiency (NUE)

Increasing fertilizers use efficiency either by the proper selection of low input

crops or by reducing the mineral losses of fertilizers has gained much importance in

present era of agriculture research (Quaggiotti et al., 2004). Humic acid, the major

source of carbon (C) improves the water holding capacity of soil and pH buffering

(McDonnell et al., 2001) which results in higher nitrogen use efficiency (NUE), and

stimulates root and shoot growth of the crops (Adani et al., 1998). Hence, when applied

to the soil, it enhances seed germination, plants resistance to drought stress, soil

aeration, drainage, soil fertility, crops yield and thus reduces the need of chemical

fertilizers (Sani and Jodaeian, 2017). The NUE of maize increases by the humic acid

application because it increases the availability of nutritional elements in the soil

solution and acts at the same time as a source and sink for the ions of N, P and K

(Vaughan and Malcolm, 1985). It also helps in reducing the detrimental effects of

chemical fertilizers on the soil and enhances the nutrient uptake by the growing crops

(Ozkutlu et al., 2006). The effect of humic acid on the uptake of nitrogen in the form

of nitrate (NO3) is found to be selective and is dependent on the concentration of its

amount and pH of the soil (Varanini and Pinton, 2000; Ghabbour et al., 2001). Abbasi

and Yousra (2012) are of the view point that higher retention of inorganic nutrients,

their availability; reduced percolation and leaching as a consequence of humic acid

application ultimately results in higher NUE. Moreover, Vaccaro et al. (2015)

conducted a field experiment and reported the considerable impact of humic acid on the

enzymes which are involved in the reduction and assimilation of N nutrient. It provides

particular bioactive molecules to the cell membranes of plants roots and increases N

uptake (Canellas and Olivares, 2014).

2.1.4.6 Impact of humic acid on grain protein and value cost ratio (VCR) of maize

crop

The application of humic acid significantly improves the grain protein content

of maize crop (Anees et al., 2016) as it consists of 0.032% inorganic N (Khan et al.,

13

2014) and N is an integral component of protein (Farhad et al., 2011). Therefore, Daur

and Bakhashwain (2013) suggested that humic acid may be used to enhance grain

protein content of maize crop as it stimulates water holding capacity of the soil along

with plant nutrients availability (Morard et al., 2013). In addition, Anees et al. (2016)

concluded that the application of humic acid in integration with mico nutrients could

prove as an important tool for enhancing value cost ratio (VCR) of maize on sustainable

and economical basis. It enhances the stability, physical and chemical conditions of the

soil, and provides resistance against its erosion by various erosion factors (Spaccini et

al., 2002). It increases biological activities in the soil (Canellas et al., 2002; Canellas et

al., 2008; Zandonadi et al., 2007) and enhances crop yield (Eyheraguibel et al., 2008).

Besides, it also has a role in the sequestration of soil pollutants (Hofrichter, 2002) and

is used in the reclamation of poor soils (Fava et al., 2004).

2.2 Nitrogen

2.2.1 The importance of N nutrient

Among the plant nutrients essential for good crop production, the role of N is

more important as it accelerates plant growth, enhances chlorophyll production, acts as

a component of plant enzymes, cell walls, DNA (deoxyribonucleic acid), RNA

(ribonucleic acid), proteins (Schrader, 1984: Marschner, 1986), amines, amides and

nucleotides (Khan et al., 2011). In Pakistan the production of maize crop is very low as

there is a shortage of nutrients in the soil, particularly nitrogen (Faisal et al., 2015). It

has a dominant role in the growth of maize because it is a nitro-positive crop (Gökmen

et al., 2001). It stimulates vegetative growth of the crop, promotes grain formation and

contributes 1-4% of plant dry matter (Onasanya et al., 2009). Moreover, it plays a vital

role in the utilization of P, K and other nutrients by the plants (Sharifi and Taghizadeh,

2009). It is considered as the major yield limiting factor in maize crop production

(Shanti et al., 1997) and its deficiency or excess may result in reduced yield of the crop

because it is proned to a number of losses; including leaching, volatilization and

denitrification etc (Sharifi and Taghizadeh, 2009). The quantity of it required for better

crop growth is dependent on the previous copping history and organic matter present in

the soil (Kang, 1981). Therefore, its proper management is of prime importance for

better crop production on sustainable basis (Iqbal et al., 2005; Khan et al., 2011) to

avoid the wastage of resources by using heavier doses of this highly costing nutrient

(Bakht et al., 2007).

14

2.2.2 Nitrogen and physio chemical properties of soil

Fertilizers have to play a vital role in the improvement of crops yield because

they are thought to bring an enhancement of 55-57% in their economic yield (Ladha et

al., 2005). N fertilizer has a specific role in improving various attributes of the soil;

however it can be lost through various unavoidable processes of leaching,

volatilization, denitrification and immobilization (Malhi et al., 2007). Nitrate (NO3-)

form of N is lost through denitrification and leaching while the ammonium (NH4+) form

is lost through the process of volatilization (Li et al., 2014). When applied in excess to

the soil, it enhances ground water pollution as well as causes many other problems (Li

et al., 2000; Canfield et al., 2010). Its application increases soil bulk density, while it

reduces the soil pH, soil porosity and field capacity of water holding (Zhong et al.,

2014). However, Sarma et al. (2013) observed that the use of inorganic N fertilizer

decreased soil bulk density (BK) and soil pH while soil porosity and water holding

capacity enhanced with its application. N fertilizer is reported to improve the total N

of soil by 203%, residual N of soil by 18-34% (Yang et al., 2007) and mineralization

of soil organic N by 4-9% (Li et al., 2003). It also enhances NO3- N content of the soil

(Malhi and Gill, 2004). Iqbal et al. (2014) indicated an increase in the soil N content

(%) through a field experiment by the application of N fertilizer. Moreover, it has a

significant impact on carbon (C) sequestration of the soil as it results in the production

of more crop residues and root exudates (Christopher et al., 2007). Therefore, Iqbal et

al. (2012) carried out a field experiment and observed maximum SOC (soil organic

content) with 160 kg N ha-1. Besides, it also has a key role in the stabilization and

improvement of organic matter in the soil (Swanston et al., 2004). It is observed in

field experiments that N have structurally abundant of phosphatase enzymes and if

sufficient N is available in the soil it enhances the phosphatase activity, mineralization

of organic P and consequently the availability of inorganic P in the soil (Wang et al.,

2007).

2.2.3 Soil organic matter and N availability

Organic matter content of the soil is generally considered as an index of

supplying N to the soil. There seems to be a close relationship between the amount of

organic matter in the soil and minerilizable N available to the plants (Sahrawat and

Narteh, 2003). The nitrogen is released from soil organic matter (SOM) through the

process of decomposition and is dependent upon the composition of decomposing

15

material and activities of the soil microorganisms (Reddy et al., 1986; Wagner and

Wolf, 2005). Decomposition is correlated to the humification, mineralization, DOM

(dissolved organic matter) and SOM (soil organic matter) stabilization. SOM performs

a dominant role in affecting soil pH, CEC (cation exchange capacity), AEC (anion

exchange capacity), soil structure, acts as a source of plant nutrients and decides soil

production capacity. However, the chemical properties of soil (soil pH and C/N ratio)

in addition to physical and climatic factors affect the rate of decomposition and

mineralization of soil organic matter (Zech et al., 1997). Soil microorganisms convert

the organic form of N in the soil through mineralization to NH4+ and then immobilize

as microbial biomass through the process of assimilation (Sylvia et al., 2005).

Furthermore, the NH4+ is converted to NO3

- through the process of nitrification. The

immobilized (assimilated) NH4+ is recycled for remineralization by soil microbes in the

future (Burger and Jackson, 2003) while some portion of it is lost through leaching

(Moller and Reents, 2009), denitrification and plant uptake (Rosecrance et al., 2000).

Decomposition of soil organic matter is primarily done with the help of bacteria and

fungi as they occupy 95% of the soil biomass (Wardle, 2002; Coleman and Wall, 2007)

while 15% of the organic matter is attributed for the continuation of their activities

(Hopkins and Gregorich, 2005).

Figure 1: General nitrogen cycle in the soil (Ghaley et al., 2015)

2.2.4 Nitrogen and crop growth

Among the plant nutrients, nitrogen has a crucial role in the growth and

development of plants (Arshad, 2003). It promotes vigorous vegetative growth, imparts

16

dark green colour to the leaves, and enlarges their size and production (Maliwal et al.,

2007). It is an integral component of various biological ingredients and stimulates the

photosynthetic activity and yield potential of crops (Cathcart and Swanton, 2003).

Grain yield of maize is related to higher N uptake and the ability to utilize the

accumulated N during its growth (Luque et al., 2006). The radiation use efficiency

(RUE) and crop growth parameters like leaf area index (LAI) and leaf longevity is

increased with the application of nitrogen (Muchow and Davis, 1988). Therefore,

optimum amount of N is necessary for enhanced nitrogen use efficiency (NUE) and

yield of maize crop (El-Gizawy and Salem, 2010) as inappropriate nutrient

management and poor soil fertility are regarded the most yield limiting factors among

other constraints (Shah et al., 2009). It has a significant impact on shoot and roots dry

weights of maize seedling as well as vigour index of the seed (Alam et al., 2003). Ayub

et al. (2003) recorded the significant impact of N fertilizer on plant height, number of

leaves plant-1, leaf area plant-1, stem diameter and dry matter accumulation of maize.

However, the crop uses only 30-50% of the inorganic N fertilizer added to the soil; the

remaining is lost by leaching, volatilization and denitrification (Stewart et al., 2005).

Depending upon the climatic conditions, soil type and crop rotation the requirement of

maize crop is different for N nutrient (Green and Blackmer, 1995).

Nitrogen is the integral component of chlorophyll which is considered the food

manufacturing company in the plant (Camara et al., 2003). It is also a component of

proteins, nucleic acids and when present is sub-optimal quantity, maize growth is

severely retarded (Haque et al., 2001) as it has fairly a large requirement for N fertilizer

(Paponov et al., 2005; Uribelarrea et al., 2009). The cultivation of same crop under

adverse climatic conditions depletes the soil out of nutritional elements and the crop

shows various deficiency symptoms of nutrients like chlorosis of leaves, necrosis and

malfunction of various biochemical and physiological processes (Bray et al., 2000;

Taize and Zeiger, 2010). Due to crops higher uptake and utilization of N nutrient, its

deficiency occurs frequently in many soil types (Ashraf and Nelly, 1994) and can be

seen in the form of disruption of pigment protein complexes and chlorophyll tissues

(Ndakidemi and Dakora, 2007). On the other hand, when sufficient N is present in the

soil it stimulates growth, delays senescence, changes the morphology of plants (Graham

and Vance, 2000) and roots proliferation in a significant manner (Robinson, 2001). The

process of leaf photosynthesis is mainly dependent on the concentration of N in the

17

leaves (Sachs and Ho, 1996). Moreover, it causes an increase in the plant height, which

is associated with the changes in phytochrome as a result of N application and is more

pronounced under nitrate form of nitrogen than ammonium (Davis and Garcia, 1983).

According to Raun and Johnson (1999), 33% of N fertilizers are used to enhance

production of cereal crops. Satisfactory results of crop production are obtained when N

is used with other sources of nutrients (Marschner, 1995).

2.2.5 Nitrogen and maize physiological growth indices

The amount of nitrogen available in the soil has a significant impact on the

growth and development of plants (Mccullovgh et al., 1994). Similarly, physiological

growth indices play an important role in the prediction of crops yield as a growth

analysis tool and indicates the events occurred during the growth stages of plants

(Hokmalipour and Darbandi, 2011). The most important growth indices (traits)

occurring during the plants growth are total dry matter (TDM), leaf dry weight (LDW),

net assimilation rate (NAR), leaf area duration (LAD), leaf area ratio (LAR), specific

leaf area (SLA), relative growth rate (RGR) and crop growth rate (CGR). They act as

an indicator for plants response to their surroundings during their life cycles (Tesar,

1984; De Sclaux et al., 2000; Anzoua et al., 2010). N application in maize crop

increases its vegetative growth and biomass production (Ogola et al., 2002). On the

ground of same reasons, Ramírez et al. (2005) arranged a field study and concluded

that N fertilizer increased dry matter production, leaf area, leaf area index, crop growth

rate, net assimilation rate and leaf area duration of maize crop. Likewise, Kumar and

Singh (2001) reported that N application significantly increased LAI, LAD, CGR, AGR

and NAR in maize crop during a field experiment. Moreover, leaf area index and leaf

area duration prove to be the important parameters for deciding dry matter

accumulation and grain yield. The growth analysis tool helps us in the adoption of better

agronomic practices for N management (Rahimzadeh et al., 2013).

2.2.6 Nitrogen and maize phenology

Nitrogen is regarded as the most critical element in affecting the phenology of

maize crop i.e. days to 50% tasseling, 50% silking and anthesis to silking interval (ASI)

(Jan et al., 2007). In addition to nitrogen, the phenology of maize is also affected by

soil moisture, temperature, light and elevated cabon dioxide (CO2) concentration in the

air (Nord and Lynch, 2009). Maximum uptake of nitrogen in maize is reported prior to

18

the tasseling and silking stages of growth (Alley et al., 2009) and N stress during these

phases results in poor grain formation, increased abortion and finally lower grain yield

of maize genotypes (Andrade et al., 2000). Therefore, in developing countries like

Pakistan, the proper N management is of crucial importance as it is highly expensive

(Khan et al., 2013) and its mismanagement at critical growth growth stages can

adversely affect maize crop phenology (Hammad et al., 2013). Dawadi and Sah (2012)

studied in a field experiment that tasseling, silking and ASI of maize crop decreased

while physiological maturity and seed fill duration (SFD) got lengthened with higher

levels of N application. Similarly, Jassal et al. (2017) observed the induced earliness in

tasseling and silking with the increase in N fertilizer. Late physiological maturity and

longer SFD as a consequence of higher N applications has also been reported by

Shrestha (2013) in maize plants. It takes active part in many physiological processes

inside the plants i.e. maintains plants photosynthetic capacity (Hageman and Below,

1984), prolongs LAD, delays senescence (Earl and Tollenaar, 1997), promotes ear and

grains initiation, contributes to sink capacity of maize (Tollenaar et al., 1994) and gives

larger final size to the grains (Jones et al., 1996). Therefore, maize crop removes 20-25

kg N from the soil for every one ton of grain produced (Muzilli and Oliveira, 1992).

The prolonged maintenance of green leaf area during seed fill duration (SFD) and the

taking up of nitrogen from the soil during this stage is considered an important

characteristic of maize genotypes for efficient N use (Dwyer et al., 1995). Moreover,

higher N utilization results in more synchronization of the flowering (Gungula et al.,

2007).

2.2.7 Nitrogen and maize grain yield

The significant role of chemical fertilizers in increasing crop production may

not be ignored since they are the primary sources of nutrients in easily available form

and maize crop has more response to their application (Obi and Ebo, 1995). They have

a dominant role in fulfilling the nutritional requirement of plants along with

improvement in physiological functions (Karasu, 2012). Many researchers have

reported an increase in the production of maize crop as a result of N application (Khan

et al., 1994) due to the stimulatory impact on its yield components (Kumar et al., 2010),

especially in those soils which are N deficient (Ayeni and Adetunji, 2010). However,

its deficiency or excess may result in lower maize yield (Karasu, 2012). It is also

reported that N application to the soil enhances the P uptake by the plants (Onasanya et

19

al., 2009) which is mostly in unavailable form and fixed in the soil (Brady and Weil,

1990). It increases P concentration in the plants due to better root growth, improved

plants potency for P absorption and translocation, decreased soil pH as a result of NH4+

absorption, enhanced solubility of P fertilizer (Havlin et al., 2003) and thus increases

biomass as well as grain yield of maize crop (Ayub et al., 2002). Increased P availability

has further a role in the uptake of K and nitrate (NO3-) by the maize plants (Ayub et al.,

2002). Keeping these facts in mind, Ogola et al. (2002) applied inorganic nitrogen (N)

to the maize crop and suggested an improvement of 25-42% in the biomass production

and 43-68% in grain yield. In addition, the grain yield is influenced by the number of

ears plant-1, ear length, grains ear-1 and 1000 grain weight (Devi et al., 2001). Any type

of stress/nutrient deficiency which may cause a reduction in these yield components

will ultimately affect the grain yield (Inamullah et al., 2011). Sharifi and Taghizadeh

(2009) carried out a field trial and observed that higher N application imporved the

plant height, ear diameter, ear length, grains row-1, grains ear-1, grains plant-1 and grain

yield of maize cultivars. Likewise, Farnia and Ashjardi (2015) studied the substantial

influence of biofertilizer N on leaf weight, stem weight, ear weight and biological yield

of maize genotypes.

Bakht et al. (2007) conducted a field trial and indicated higher ear length, 1000

grain weight, grains ear-1, stalk yield and grain yield in maize crop at 200 kg N ha-1. In

a previous field experiment, it was observed that 240 kg N ha-1 produced higher 1000

grain weight, grains ear-1, grain weight ear-1, stover yield and grain yield (Sanjeev et

al., 1997). Furthermore, Inamullah et al. (2011) revealed in a field experiment that N

application of 300 kg ha-1 produced maximum ears plant-1, ear length, 1000 grain

weight, grains ear-1, economic yield, biological yield and harvest index (HI). The

increase in number of ears plant-1 and yield is due to the enhancement in plant dry

matter and fresh biomass (Jokela and Randall, 1989; Sharifai et al., 2012). In addition,

Chung et al. (2000) studied that the integrated use of N and organic sources of nutrients

enhanced maize crop dry matter accumulation many times, as it is an aggressive utilizer

of available plant nutrients (Ayoola and Makinde, 2009). Sorkhi and Fateh (2014)

demonstrated the significant impact of 150 kg N ha-1 on number of ears plant-1, grains

ear-1 and grain weight of maize. Similarly, Fedotkin and Kravtsov (2001) reported best

growth and grain yield with the application of 240 kg N ha-1. In a similar study, Gökmen

et al. (2001) while investigating the impact of N fertilizer on yield and yield

20

components of maize found that plant height, ear length, grain yield and 1000 grain

weight improved in a linear way with the application of N fertilizer. Mahmood et al.

(2001) reported the significant effect of inorganic N fertilizer on maize plant height,

grains ear-1, thousand grain weight and HI. Similarly, Abouziena et al. (2007) and

Akmal et al. (2010) concluded that by increasing the N level, 1000 grain weight is

enhanced. Moreover, Akhtar (2001) reported linear relationship among yield and yield

components of maize and N fertilizer. Efficient utilization of solar radiations, greater

assimilates production and their conversion to starches results in higher grains ear-1 and

weight plant-1 that produce heavier biomass as well as seed yield (Derby et al., 2004).

Likewise, Arif et al. (2010) had reported earlier that number of ears m-2, rows ear-1,

grains ear-1, ear weight, 1000 grain weight and economic yield of maize crop was

substantially affected by increasing N application rates. It is because; N is an integral

component of protein and amino acids (Bakht et al., 2007) and promotes plant growth

by controlling various physiological processes of the plants. Its deficiency causes

reduced yield, small grain size and stunted growth in the crop (Bakht et al., 2007).

2.2.8 Impact of nitrogen on NUE (nitrogen use efficiency) of maize

Proper N management is of vital importance in crop production, as it increases

NUE and helps to exploit the genetic potential of maize hybrids for better grain yield

(Taghizadeh and Sharifi, 2011). Besides farmers’ real benefits and high production, it

also decreases the leaching of N fertilizer below the root zone of crop (Rahmati, 2009).

It is reported that NUE is decreased with increasing the levels of N fertilizer (Limon-

Ortega et al., 2000: Zhao et al., 2006) and the increase in yield is less than the amount

of fertilizer supplied to the soil (López-Bellido and López-Bellido, 2001). Raun and

Johonson (1999) observed that only 33% of N applied to the soil is utilized by cereal

crops as NUE is variable and dependent upon various factors. It is affected by climatic

conditions, soil type, crop species, rate and time of N application (Raun and Johonson,

1999; Halvorson et al., 2001). The selection of N efficient maize genotypes may prove

another alternative strategy for improving NUE apart from N management techniques

(Mi et al., 2007). They respond to the low N supply by a change in the root to shoot

ratio and translocation of assimilates from shoots to roots (Tian et al., 2005; Wang et

al., 2003). To determine the NUE of a maize genotype, two factors are involved. One

is the nitrogen uptake efficiency of a cultivar in terms of N removal from the soil. N

utilization/physiological efficiency is the other factor which is responsible for efficient

21

NUE (Moll et al., 1982). There is a significant relationship between N accumulation in

the plant and NUE, and the grain yield is mostly affected by limited N uptake from the

soil (Sinclari and Vadez, 2002). It means N uptake is more important in crops as

compared to N utilization regarding NUE (Horst et al., 2003).

Grain development

Photoassimilate

Green leaf area

-fast expansion

-late senescence N retranslocation

Higher N accumulation

Root

-size

-architecture

N supply in soil

Figure 2: Physiological processes of NUE in maize crop (Mi et al., 2007)

2.2.9 Nitrogen and maize quality

High quality of seeds is a desirable characteristic in crops for their survival

(Sebetha et al., 2012). N fertilization is considered a major element in enhancing the

grain yield and quality of maize crop (Alam et al., 2003). Moreover, its application

increases the vigour and viability of seeds in a considerable way (Sebetha et al., 2015).

Previous research showed that optimum amount of N is necessary for improved protein

content in seeds (Almas, 2009) as low and high doses of N are detrimental for maize

seed quality (Stone et al., 1998). Therefore, nitrogen fertilizers appear to be the primary

cause of increase in 1000 grain weight and protein content of maize seed (Khan et al.,

2011). As observed in a field study, Ullah et al. (2015) found that quality parameters

like chlorophyll content, crude fiber, ash, and crude protein (%) of maize plants

22

considerably got improved with increase in N levels as compared to lower ones.

Likewise, Zhang et al. (2010) reported in a field trial that 375 kg N ha-1 enhanced the

protein and lysine contents of the grain with a decrease in the starch content. The quality

of maize seed is closely related to endosperm of the seed which makes up 85% of the

total dry weight of the seed and contains 70% of the protein (Cheetham et al., 2006).

Furthermore, the endospermic properties are primarily determined by N fertilizer

application (Sabata and Mason, 1992). N fertilizer has a vital role in increasing seed N

(%) and zein component of seed (Tsai et al., 1992) which is the principal component of

endospermic protein. The function of zein protein is very important in deciding the

texture of the maize seed (Abdelrahman and Hosney, 1984). Nitrogen is essential for

plants metabolic functions and has a special role in photosynthesis, tillering and stalk

elongation (Koochekzadeh et al., 2009). Its deficiency causes reduction in leaf area,

lowers photosynthesis and results in suppression of crop quality and yield (Sreewarome

et al., 2007). Hence, El-Hassan et al. (2014) while conducting an experiment reported

that nitrogen fertilizer markedly increased the N concentration of grains in the maize

crop.

2.2.10 Effect of nitrogen on value cost ratio (VCR) of maize

The significant impact of N may not be denied in obtaining higher economic

return, also known as VCR as it has a critical role in increasing crop yield (Almas,

2009). VCR is regarded as the net return of money invested on crop production and

depends on the cost of fertilizer. When VCR value is 2 it indicates more than 100%

return of the cost incurred on fertilizer. A VCR lesser than 2 represents that margin

return of farmer’s becomes uneconomical (Dilshad et al., 2010) and risk exists for

investing his money in the crop production either due to poor management practices or

bad weather conditions (Dilshad et al., 2010). However, it is not always useful as it

does not take in to account the residual effect of previous fertilizers applied to the

preceding crop and higher VCR usually occurs at the lower end of the cost of fertilizer

(Dilshad et al., 2010). In a poor country like Pakistan, there is excessive use of N

fertilizer in relation to phosphatic and potash fertilizers (Bumb et al., 1996) which

results in imbalanced nutrition of fertilizers. In addition to lower net economic returns

(VCR), it also causes environmental and soil degradation problems (Cisse and Amar,

2000). On the other hand, its stress (seeding-V8, and V8-maturity stages) in maize crop

cuases a reduction of 30% and 22% in yield (Subedi and Ma, 2005). Therefore, the

23

judicious use of N fertilizer is must in cereal crops to achieve higher yield on sustainable

basis. Ullah et al. (2015) carried out a field experiment and reported maximum VCR

(value cost ratio) in Kisaan variety of maize at 240 kg N ha-1.

2.2.11 The effect of humic acid and nitrogen on growth, yield and quality of maize

Humic acid is enumerated as one of the main natural product used for enhancing

crop production on sustainable basis (Shafeek et al., 2013). It plays a dominant role in

the release of primary nutrient N (Azeem et al., 2014) which contributes 1-4% of plants

dry matter (Haque et al., 2001). It is released from humic acid up to 20 kg HA ha-1 and

requires almost 60 days to complete the process (Sathiyabhama et al., 2003) because it

is a slow release fertilizer of N (Dev and Bhardwaj, 1995). Nitrogen is the main

deciding factor in enhancing maize grain yield and quality (Haque et al., 2001). For the

same reasons, Azeem et al. (2015) carried out a field study and reported that humic acid

and N integration considerably increased leaf area (LA), crop growth rate (CGR), grain

yield and biological yield of maize crop while leaf area index (LAI) and net assimilation

rate (NAR) was only affected by nitrogen fertilizer. Furthermore, N supplied to the crop

will affect the amount of chlorophyll, protein and protoplasm formed in the plants.

Therefore, proper N supply must be ensured to the growing plants during their whole

life cycle so that vegetative and reproductive growth may no be restricted (Zhang et al.,

2008) and it is possible only through humic acid integration. Moreover, it has a

considerable impact on the quality of various crops (Yildirim, 2007) and brings an

improvement in the amount of different phytochromes i.e. auxins, cytokinins and

gibberellic acid (Abdel et al., 2007). The auxin contained in humic acid stimulates the

cell division, stem elongation and increases the stretching capacity of the cell walls. So

the humic acid has a great contribution in the improvement of protein and oil content

(quality) of seed as well as its individual weight (Singaravel et al., 1993). The seed

quality has a substantial impact on the success of the planted crop and its yield potential

(Bewely and Black 1994). Moreover, Bakry et al. (2013) suggested in a field study that

foliar application of humic acid at the rate of 13 mg L-1 increased the growth, yield and

yield components of wheat crop. However, Khan et al. (2010) recorded higher yield of

wheat at 3 kg HA ha-1.

2.3 Maize genotypes

The current yield of maize crop in Pakistan is very low (Javed et al., 2006), so

there is a dire need to select those genotypes which have higher yield potential as well

24

as greater climatic adaptation (Tahir et al., 2008). The use of high yielding maize

genotypes is essential not only for getting higher grain yield but also for improving the

quality of the harvest and income per unit of the harvest (Abbas, 2001). The nutrients

efficient utilization is dependent on the genetic potential of different plant species and

cultivars (Jan et al., 2007). Therefore, in order to reap the full yield potential of various

maize genotypes, the factors of production may be managed in such a way so that they

may not reduce their yield as growth constraints (Jan et al., 2007).

2.3.1 Maize genotypes and nitrogen

It is reported that nitrogen is the most deficient element in our crop production

system (Tolessa et al., 2007) and maize genotypes have quite differential responses to

N fertilization regarding their yield potential and growth characteristics (Chaudhry et

al., 2005; Sharifi and Taghizadeh, 2009). Based on these characteristics, high

performance maize genotypes are grown in those soils which are fertile and have

sufficient amount of N nutrient. These genotypes are not suitable for N deficient soils

and resource poor farmers (Bänziger et al., 1997). Therefore, the resource poor farmers

are not in such a financial position to exploit the yield potential of these genotypes. The

alternative solution to these constraints is the selection of those maize genotypes which

are efficient in N use under both N limited and excess conditions (Smith et al., 1995).

These genotypes have quite different physiological growth indices like net assimilation

rate (NAR), leaf area index (LAI), leaf area duration (LAD), crop growth rate (CGR)

(Luque et al., 2006; Azadgoleh and Kazmi, 2007) which lead towards different grain

yield (Ahmed, 2011). Eghball and Maranville (1991) observed an increase of 19% in

the yield of N efficient genotypes over old maize hybrids. Similarly, McCullough et al.

(1994) suggested in a field study that the tolerance of newly released maize hybrids is

more to N limited conditions than older varieties especially in the early growth stages

with respect to chlorophyll content, rate of leaf initiation, photosynthesis and stomatal

conductance. That is why, it was observed that hybrid S.C-10 out yielded hybrid

T.W.C-310 in terms of plant height, green leaves plant-1 and leaf area plant-1, while the

hybrid T.W.C-310 was superior S.C-10 in most growth characteristics (Mansour, 2009)

and grain yield (Abd El-Maksoud and Sarhan, 2008).

25

2.3.2 Maize genotypes and NUE

Among cereal crops, maize has the highest production capacity and requirement

for N fertilizer (Sivasankar et al., 2012). As a consequence, any attempt to bring an

improvement in the N efficiency will ultimately reduce environmental hazards and will

be cost effective also (Garnett et al., 2015). In addition to better N management

techniques, the use of improved germplasm may be helpful in increasing NUE which

depends upon two factors i.e. NUpE (nitrogen uptake efficiency) and NUtE (nitrogen

utilization efficiency) (Good et al., 2004). The NUpE and NUtE is further dependent

upon the N level of the soil. Under high N supply in the soil, NUpE is more important

while in case of limited N supply NUtE is important (Moll et al., 1982). Under less than

40% supply of N in the soil, the nitrogen uptake efficiency of cereal crops becomes

very poor (Sylvester-Bradley and Kindred, 2009). Nitrogen is available to the plants in

two forms i.e. nitrate (NO3-) and ammonium (NH4

+). The NO3- form of N fertilizer is

abundant in the soil and thus makes a greater contribution in the N uptake of plants

(Miller et al., 2007). It is a highly mobile anion and its uptake is related to the absorption

capacity of the plants roots (Zhong et al., 2014). The NH4+ fraction forms only 10% of

nitrate (NO3-) concentration in the soil but is still significant in the overall N uptake of

plants (Miller et al., 2007). It is less mobile in the soils but the absorption capacity of

roots is still important for its uptake as compared to other immobile nutrients like P

(Clarkson, 1985). Moreover, variation is observed among maize genotypes regarding

the utilization of N with respect to the absorbed N and total N in the soil as a result of

N fertilizer application (Duncan and Baligar 1990). Keeping in view these genetic

variations, the use of maize genotypes with a high NUE potential on soils with low N

content is the best option (Tolessa et al., 2007) which may help in reducing the adverse

impact of N deficiency on maize crop production (Wiesler et al., 2001).

2.3.3 The impact of maize genotypes on the growth and yield traits of maize

The agronomic traits of primary importance in maize are days to tasseling, days

to silking, plant height, ear height, branches tassel-1, leaf area, grains ear-1, ear weight,

1000 grain weight and grain moisture percentage (Malik et al., 2005). Among various

growth traits, the grain yield is the most critical and complicated quantitative trait in

maize crop. It is controlled by many genes (Zdunic et al., 2008). The improvement of

grain yield is the main focus of our research programs while releasing new maize

genotypes. It is the final product of various processes occurring during the life cycle of

26

plants (Prado et al., 2014). Being a complex trait, it is influenced by different yield

contributing factors, like number of grains ear-1 and 1000 grain weight, plant height and

ear height (Moznur Rahman et al., 1995). Out of these yield contributing factors, the

number of grains is subjected to great variation (Borrás and Gambín 2010). Grain

weight is a markedly heritable characteristic (Sadras 2007; Prado et al., 2013a) and is

highly varying among the maize genotypes (Khan et al., 2016). The yield of inbred

lines from diverse stock is higher than crosses of inbred lines from the same variety

(Malik et al., 2005). Ear weight and ear circumference can contribute directly and

significantly to the grain yield and much improvement in yield can be brought about by

proper selection for grain yield (ÖZ, 2012), plant and ear height (Prodhan and Rai,

1997). It is positively correlated to the grain set (Otegui et al., 1995) which is very

sensitive to the prevailing weather conditions during tasseling and silking (Tollenaar et

al., 2002) stages of maize growth. Therefore, crop phenology is considred the most

important characteristic in deciding maize crop production (Cárcova and Oteguai,

2001). Dawadi and Sah (2012) reported different phenological traits in various maize

genotypes. Likewise, Grzesiak (2001) studied remarkable genotypic variation among

different maize genotypes for their growth and yield traits.

The variation in genetic potential of maize genotypes is a major component

responsible for variable yield (Munawar et al., 2013). Ihsan et al. (2005) recorded

significant genetic variations in maize genotypes for different morphological

characteristics. Variability is considered a key to crop improvement. Tadesse (2012)

conducted a field study and observed significant differences among maize genotypes

regarding plant height, ear height, number of ears plant-1, grain yield and 1000 grain

weight. In a similar study, Langade et al. (2013) reported that days to 50% tasseling,

50% silking, plant height, ear height, ear length, ear diameter, grains ear-1, grain yield,

1000 grain weight, oil content, protein content, starch content and sugar content were

varying among maize genotypes. The genotypes final yield is highly correlated to the

grain weight attained during grain formation. The trait of grain weight is further related

to the moisture content and dry matter accumulation (Rondanini et al., 2007). The phase

of dry matter accumulation is divided into three phases (the lag phase, the grain fill

duration and the drying phase of maturation) (Bewley and Black, 1985). The period of

lag phase is characterized by rapid cell division, increase in water content and no dry

matter accumulation. The grain fill duration (GFD) is a period of rapid dry matter

27

accumulation and the final weight of grain is mostly related to this phase. Most

genotypic differences in grain weight are dependent on grain growth rate (GGR) during

this phase. Reduction in grain moisture content (MC) is observed throughout this phase.

After a critical MC, there is no dry matter accumulation and the phase of physiological

maturity is attained (Shaheb et al., 2015). These traits are variable among various maize

genotypes (Borrás et al., 2009).

2.3.4 Maize genotypes and humic acid

Humic acid acts as carrier of minerals, plays the role of catalyst in various

biochemical reactions and performs the function of antioxidant in the maize genotypes

(Kulikova et al., 2005). It takes part in various metabolic reactions of the plants and

controls their physiological processes (Yang et al., 2004). Therefore, Shahryari et al.

(2011) evaluated the impact of humic acid on maize genotypes and found that it

significantly affected their germination and seedling growth. The impact was more

pronounced on the length of their primary roots which helped in the establishment of a

good maize crop stand in the field. Among the maize genotypes, the relative root growth

of 794 and ZP434 was more affected which were single crosses. Moreover, high

chlorophyll index was observed in single cross 704 and 505. They suggested that if

used in a small quantity, these organic fertilizers might influence the plant growth in a

much better and marked way. Furthermore, Mohammadpourkhaneghah et al. (2012)

carried out a field experiment and reported the significant influence of humic acid

(leonardite based humic acid and peat based humic acid) on the grain yield and

agronomic traits of mize genotypes. Leonardite based humic acid increased biological

yield by 46.89% while peat based humic acid increased biological yield by 34.47%.

Likewise, leonardite based humic acid improved grain yield by 74% while peat based

humic acid brought an improvement of 44.7%. However, the increase in yield is related

to the source of humic acid, quality, its concentration, cropping systems and types of

soils (Seyedbagheri, 2008). It not only improves the grain yield of maize genotypes but

also leads towards sustainable agriculture. The genotype OS499 exhibited higher 1000

grain weight while single cross showed lower 1000 grain weight. Similarly, the highest

number of ears plant-1 was recorded in the maize genotype ZP677 while lower number

was calculated in the genotype ZP434 (Mohammadpourkhaneghah et al., 2012).

28

3. MATERIALS AND METHODS

A field study was designed for two consecutive years of 2014 and 2015, to

evaluate the vital role of humic acid in integration with different levels of N on the

growth and yield potential of different maize genotypes as well as physico-chemical

properties of soil under the agro climatic conditions of District Swabi, Khyber

Pakhtunkhwa, Pakistan.

3.1 Experimental site

The site where the experiments were conducted is located at 34° 7' 12 N and

72° 28' 12 E at District Swabi (Agricultural Research Station, Swabi). The experimental

site is characterized by sub-tropical, semi-arid, hot and continental climate having an

average annual precipitation of 568 mm. Moreover, the average maximum temperature

in the summer (from May to September) is 39.5C and the average minimum

temperature is 23.5C. The average minimum temperature in the winter (from

December to March) is 5.3C and the maximum average temperature is 21C. In the

summer season the average rainfall is usually lower than in the winter. Higher amount

of winter precipitation (rainfall) is reported in the months of January and February while

for monsoon season the higher summer precipitation is recorded in August.

Table 1.1 Average air temperature (C) and rainfall (mm) at ARS, Swabi,

Khyber Pakhtunkhwa during the year 2014 and 2015.

Month

2014 2015

Max T

(C)

Min T

(C)

Rainfall

(mm)

R. H (%) Max T

(C)

Min T

(C)

Rainfall

(mm)

R. H (%)

January 18.1 1.9 81.4 63.14 18.5 2.1 26.0 59.27

February 20.2 2.8 56.8 72.08 19.6 7.4 41.2 68.39

March 26.7 9.4 73.1 60.31 24.9 10.8 84.3 62.14

April 32.3 16.5 33.6 57.28 30.2 15.2 46.1 61.76

May 37.4 20.1 34.8 47.21 39.8 21.3 13.4 41.87

June 42.9 24.7 48.3 51.83 42.9 25.7 37.1 48.92

July 40.7 25 74.5 75.67 41.3 26.2 78.6 71.40

August 38.6 24 82.3 67.85 39.4 24.7 81.2 63.37

September 35.1 21.2 48.7 55.40 37.1 22.8 58.0 59.24

October 32.4 15.4 06.1 51.73 34.3 17.4 62.0 47.59

November 26.2 8.2 09.2 64.26 26.5 9.3 18.6 56.73

December 19.3 4.2 36.5 68.42 20.6 4.5 04.1 62.30

29

Figure 1.1: Average air temperature (oC) and rainfall (mm) at ARS, Swabi,

Khyber Pakhtunkhwa during the year 2014.

Figure 1.2: Average air temperature (oC) and rainfall (mm) at ARS, Swabi,

Khyber Pakhtunkhwa during the year 2015.

0

10

20

30

40

50

60

70

80

90

100

110

120

0

10

20

30

40

50

60

70

80

90

100

Rain

fall

(m

m)

Tem

per

atu

re (

oC

)

Months

Maximum Temperature (°C)

Minimum Temperature (°C)

Rainfall (mm)

Relative humidity (%)

0

10

20

30

40

50

60

70

80

90

100

110

120

0

10

20

30

40

50

60

70

80

90

100

Rain

fall

(m

m)

Tem

per

atu

re (°C

)

Months

Maximum Temperature (°C)

Minimum Temperature (°C)

Rainfall (mm)

Relative humidity (%)

30

3.2 Pre-experimental soil analysis

Soil analysis was done in the central laboratory of Agricultural Research

Institute, Tarnab Peshawar (Table 1.2). Prior to starting the trial, 3 soil samples were

collected randomly from various locations in the field at a depth ranging from 0 to 15

cm by using soil Auger. A composite sample was formed by mixing all the samples

together. After drying in the air, the sample was sieved (using 2 mm mesh) to remove

stones, mulches and other unwanted materials. Percent clay, silt and sand were

determined by hydrometer method (Tagar and Bhatti, 1996) using a textural triangle

as indicated in table 1, where physicochemical properties of the sample are also given.

Soil bulk density was determined from composite samples of the soil using core

samplers (Rowell, 1994). Soil organic matter was estimated by the procedure as

described by Ball (1964). pH of the soil was measured in a suspension of soil and water

(1:5) after half an hour of stirring while reading on pH meter (using glass and calomel

electrodes) as suggested by Page et al. (1982). Electrical conductivity (EC) was

calculated by the procedure of Rhoades (1996). The Soltanpour and Schwab (1977)

method of AB-DTPA (Ammonium Bicarbonate-Diethyl Triamine Penta-Acetic

extractable) was used for the estimation of P and K, using spectrophotometer and flame

photometer. The Kjeldhal method of Bremner and Mulvaney (1982) was used for

calculation of total N in soil.

Table 1.2 The physico-chemical properties (basic characteristics) of the

composite soil sample.

Physical characteristics Units Depth (0-15cm)

Sand % 10.1

Silt % 69.7

Clay % 20.2

Texture class - Silt loam

Bulk density (g cm-3) 1.33

Chemical properties

pH - 7.9

EC dS m-1 0.07

Organic matter % 0.48

Available P content mg kg-1 4.72

Total N content % 0.047

K content mg kg-1 183.0

31

3.3 Experimental design, factors and treatments combination

The experiment was carried out in Randomized Complete Block Design

(RCBD) with split-split plot arrangement having three replications. Maize genotypes

(G1, G2, G3 and G4) were planted in the main plots, while humic acid (HA) and nitrogen

levels were applied to subplots and sub-subplots respectively. Each sub-subplot was

having an area of 4.9 m x 3 m (14.7 m2). Four maize genotypes i.e. 3025, 55W65

(hybrids), Jalal and Iqbal (locally developed high yielding latest open pollinated

varieties in Khyber Pakhtunkhwa) were grown on 02-07-2014 and 03-07-2015 during

both the years. Plant to plant distance of 20cm and row to row distance of 70cm was

maintained for maize sowing by hand (manual dibbling method). Varying

concentrations of humic acid were used in integration with different levels of nitrogen

during the experiments. Nitrogen was given to the maize sub-subplots at the rate of 0,

120, 180 and 240 kg ha-1 from the source of urea {Co(NH2)2} fertilizer, while humic

acid (0, 0.6, 1.2 and 1.8 kg ha-1) was applied to the subplots. The desired levels of 0.6,

1.2 and 1.8 kg HA ha-1 were obtained from 300, 600 and 900 litres of 2000 ppm (2 g

liter-1) humic acid solution respectively. The humic acid was extracted in the National

Agricultural Research Center, Islamabad from the available brown coloured matured

and dried wate materials of sunflower (Helianthus annuus L.) in the form of a

commercial product. The extraction method of humic acid from sunflower is as under.

1. Matured and dried waste plant materials of sunflower were soaked overnight

and extracted with 0.01 M KOH (potassium hydroxide) solution.

2. The extract was filtered, centrifuged and then acidified with 0.01 M HCL

(hydrochloric acid).

3. The acidified humic acid was filtered and collected in a container. The elemental

analysis revealed that it had 0.032% N (Kjeldahl), 0.89% P (spectrophotometer

method), 2.12% K (flame photometer), 0.41 mg kg-1 Fe and 0.45 mg kg-1 Zn

(atomic absorption spectrophotometer), while its carbon content was 54%

(Khan et al., 2014).

The experimental plots were irrigated and when the field moisture status

reached to a proper level (wattar), a good seed bed was prepared with the help of

primary and secondary tillage implements (cultivator and rotavator). Soil test was done

to find out fertility status of the soil. The recommended dose of phosphorous (100 kg P

ha-1) was applied as a basal dose from the source of SSP fertilizer having 18% P. It was

32

added to the soil during seed bed preparation and mixed completely. For the control of

weeds the weedicide “primextra 500 WP” was applied before the emergence of seed.

The required N doses (0, 120, 180 and 240 kg ha-1) were added to the crop in two split

applications: 1st 17 days after sowing (DAS) and 2nd 35 days after sowing (DAS) while

humic acid at different levels (0, 0.6, 1.2 and 1.8 kg ha-1) was mixed with water and

applied to the soil at seedling stage of the crop in a single dose by using the fountain.

30 DAS, the crop was sprayed with the insecticide “chlorpyrifos, 40% EC” as a

precautionary measure for the control of insects and stem borer. Five irrigations were

applied to the crop from sowing till the harvesting. The detail of treatments is given

below.

Main plot

Maize genotypes

G1 = 3025

G2 = 55w65

G3 = Jalal

G4 = Iqbal

Subplot

Humic acid

Humic acid levels

H0 = 0 kg HA ha-1 (without application of HA)

H1 = 0.6 kg HA ha-1

H2 = 1.2 kg HA ha-1

H3 = 1.8 kg HA ha-1

Sub-subplot

Nitrogen levels

N0 = 0 kg N ha-1

N1 = 120 kg N ha-1

N2 = 180 kg N ha-1

33

N3 = 240 kg N ha-1

Data were collected on the following parameters during the course of study:


development and phenology of maize genotypes

3.4.1 Days to emergence

3.4.2 Days to 50% tasseling

3.4.3 Days to 50% silking

3.4.4 Anthesis to silking interval (ASI)

3.4.5 Days to physiological maturity

3.4.6 Seed fill duration (SFD)

3.5 The effects of the integration of humic acid with nitrogen on plant growth

of maize genotypes

3.5.1 Total weight (g) plant-1 at silking

3.5.2 Ear weight plant-1 at silking

3.5.2 Plant height (cm)

3.5.3 Absolute growth rate (AGR) at silking

3.5.4 Crop growth rate (CGR) at silking

3.5.5 Total weight (g) plant-1 at maturity

3.5.6 AGR at maturity

3.5.7 CGR at maturity

3.6 The effects of the integration of humic acid with nitrogen on leaf growth

and development of maize genotypes

3.6.1 Leaves plant-1 at silking

3.6.2 Leaf dry weight plant-1 at silking

3.6.3 Leaf area plant-1 at silking

3.6.4 Leaf area index (LAI) at silking

3.6.5 Specific leaf area (SLA) plant-1 at silking

34

3.6.6 Leaf area ratio (LAR) plant-1 at silking

3.7 The effects of the integration of humic acid with nitrogen on yield and yield

related attributes of maize genotypes

3.7.1 Productive plants m-2

3.7.2 Ears plant-1

3.7.3 Ears m-2

3.7.4 Ear weight (g) plant-1 at maturity

3.7.5 Ear length (cm)

3.7.6 Ear girth (cm)

3.7.7. Rows ear-1

3.7.8 Grains row-1

3.7.9 Grains ear-1

3.7.10 1000 grain weight (g)

3.7.11 Biological yield (kg ha-1)

3.7.12 Grain yield (kg ha-1)

3.7.13 Stover yield (kg ha-1)

3.7.14 Harvest index (%)

3.7.15 NUE-AE (kg grains kg-1 N)

3.7.16 NUE-PFP (kg grains kg-1 N)

3.7.17 NAR (30-75 DAS) (g m-2 day-1)

3.7.18 Grain protein (%)

3.8 The effects of the integration of humic acid with nitrogen on soil properties

3.8.1 Soil phosphorous content (mg kg-1) at maize harvest

3.8.2 Soil nitrogen content (%) at maize harvest

3.8.3. Soil organic matter (%) at maize harvest

3.9 Economic analysis of the integration of humic acid with nitrogen

35

3.10 Meteorological Data

3.10.1 Maximum and minimum temperature (C)

3.10.2 Total rainfall (mm)

3.10.3 Relative humidity (%)

3.11 Procedure for Data Recording

3.11.1 The effects of the integration of humic acid with nitrogen on plant


3.11.1.1 Days to emergence

For each experimental unit the date when most of the young seedlings had

emerged was recorded. Days to emergence are referred to the number of days

from the seed sowing to the day when seedling emerged from the soil surface.

3.11.1.2 Days to 50% tasseling

The number of days to 50% tasseling was recorded on five randomly selected

uniform plants. When more than 50% plants developed tassels, days were

counted.

3.11.1.3 Days to 50% silking

Data were recorded on days to 50% silking on five randomly selected uniform

plants. Days were counted when more than 50% of plants develop silks.

3.11.1.4 Anthesis to silking interval (ASI)

ASI was reported as the number of days counted from tasseling to silking stage

of the maize growth.

3.11.1.5 Days to physiological maturity

Days were calculated from sowing date to plant maturity i.e. a point of growth

when there is no more dry matter accumulation in the maize plants (the grain

moisture content is about 20-25%).

3.11.1.6 Seed fill duration (SFD)

Harvest maturity date - days to silking

36

3.11.2 The effects of the integration of humic acid with nitrogen on plant growth

of maize genotypes

3.11.2.1 Total weight plant-1 at silking

Five plants were taken after harvesting from the side rows of each sub-subplot,

dried and finally weighed to calculate data on total weight plant-1.

3.11.2.2 Ear weight plant-1 at silking

Ears were separated from the selected plants at silking stage, dried and weighed

for taking data on dry weight of ear plant-1 on average basis.

3.11.2.3 Plant height (cm)

Five plants were taken at random in each treatment, and then the length

measured from ground level to the top of tassel by using a measuring tape. Then

the average was calculated.

Data on derived physiological parameters of maize was taken by using the

following formulae used by Amanullah (2004).

3.11.2.4 )( 11 dayplantgsilkingtoDays

plantperWeightsilkingatAGR

3.11.2.5 )(. 122 daymgmplantsofNosilkingtoDays

plantperWeightsilkingatCGR X

3.11.2.6 Total weight plant-1 at maturity

Five plants were taken and harvested from the side rows of each sub-subplot,

dried and finally weighed to calculate data on total weight plant-1 as suggested

by Amanullah (2004).

3.11.2.7 )( 11 dayplantgmaturitytoDays

plantperWeightmaturityatAGR

3.11.2.8 )(. 122 daymgmplantsofNomaturitytoDays

plantperWeightmaturityatCGR X

3.11.3 The effects of the integration of humic acid with nitrogen on leaf growth


3.11.3.1 Leaves plant-1

37

At silking five maize plants were selected randomly from each sub-subplot.

Their numbers of leaves were counted and then average was worked out.

3.11.3.2 Leaf dry weight plant-1 at silking

At least five plants were randomly harvested from each sub-subplot. Leaves

were removed, dried and then weighed for reporting data on dry weight of leaf

plant-1.

3.11.3.3 Leaf area plant-1 (cm2) = Average leaf area x number of leaves plant-1

Where

Leaf area (cm2) = Leaf length (cm) x Leaf width (cm) x 0.75 (Montgomery,

1911)

3.11.3.4 Leaf area index (LAI) = Leaf area/Ground area

(LAI = Leaf area plant-1 x Number of plants/m2).

Data on derived physiological parameters of maize was taken by using the

following formulae used by Amanullah (2004).

3.11.3.5 )( 121 gcmplantperweightLeaf

plantperareaLeafsilkingatplantSLA

3.11.3.6 )( 121 gcmplantperWeight

plantperareaLeafsilkingatplantLAR

3.11.4 The effects of the integration of humic acid with nitrogen on yield and yield


3.11.4.1 Productive plants m-2

Data regarding productive plants m-2 was calculated by using the following

formula:

rowsofNomcedisRRmlengthRow

plantsofNumbermplantsoductive

XX .)(tan)(Pr 2

3.11.4.2 Ears plant-1

For calculating ears plant-1, plants were counted in one row of each sub-subplot

and then ears plant-1 according to the following formula:

38

plantsofNumber

earsofNumberplantearsofNumber 1

3.11.4.3 Ears m-2

Ears at maturity m-2 were calculated by using the following formula:

rowsofNomcedisRRmlengthRow

earsofNumbermearsofNumber

XX .)(tan)(

2

3.11.4.4 Ear length (cm) at maturity

After harvesting and dehusking, the length of five ears was recorded and then

averaged. Foot was used for measuring.

3.11.4.5 Ear girth (cm) at maturity

After harvesting and dehusking, the girth of five ears was recorded and then

averaged. Foot was used for measuring.

3.11.4.6 Ear weight plant-1 at maturity

Five ears from the plants at maturity were taken, dried, weighed and then

average calculated.

3.11.4.7 Rows ear-1

Took five samples of ears from each sub-subplot and then calculated average of

grain rows ear-1.

3.11.4.8 Grains row-1

Grains row-1 were counted by taking the ears grains of five selected plants.

3.11.4.9 Grains ear-1

Took five ears from each sub-subplot at maturity and then after shelling

manually, determined the number of grains ear-1.

3.11.4.10 1000 grain weight (g)

From each treatment, 1000 grains at random were taken and weighed.

39

3.11.4.11 Biological yield (kg ha-1)

At final maturity of the crop (when there is no accumulation of dry matter

further) biological yield was recorded by weighing stalks along with the ears

using spring balance in each treatment of the experiment.

3.11.4.12. Grain yield (kg ha-1)

Three central rows were harvested; the ears were dehusked, dried and shelled.

The weight of grain was calculated and then converted into kg ha-1.

)()(tan.

10000)()(

21

mlengthRowmcedisRRharvestedrowsofNo

mkgyieldGrainhakgyieldGrain

XX

X

3.11.4.13. Stover yield (kg ha-1)

The stover yield was determined by subtracting grain yield from the biological

yield and then converted to (kg ha-1) i.e.

)()(tan.

10000)()(

21

mlengthRowmcedisRRharvestedrowsofNo

mkgyieldStoverhakgyieldStover

XX

X

3.11.4.14 Harvest index (%)

The data on HI was recorded by the following formula:

100)(log

)((%)

1

1

X

hakgyieldicalBio

hakgyieldGrainindexHarvest

3.11.4.15 )(

)(1

hakgappliedNitrogen

NwithoutyieldGrainNwithyieldGrainAENUE

3.11.4.16. )(

)(1

1

hakgappliedNitrogen

hakgyieldGrainPFPNUE

( Dobermann, 2007).

3.11.4.17. Net assimilation rate (NAR)

Net assimilation rate (NAR) was calculated at specified intervals (30-75 DAS)

in g m-2 day-1 from the dry weight and leaf area of plants as given by Beadle

(1993).

)( 12 daymgLAD

TDMNAR

40

TDM denotes total dry matter, and LAD denotes leaf area duration.

Where LAD = (LAI1 + LAI2) x (t2 – t1)/2

and LAI1 = Leaf area index at t1, LAI2 = Leaf area index at t2, t1 = Time of first

observation, t2 = Time of second observation.

3.11.4.18 Grain protein concentration (%) at maize harvest

The total amount of N in maize seeds was calculated by the Bremner and

Mulvaney (1982) method, which is known as Kjeldahl method. According to

this method a given weight of seeds (0.2 g) were digested for an hour in

sulphuric acid (H2SO4) (4 ml, concentrated) along with a suitable catalyst (¼

tablet). The digest was cooled down and 40% NaOH solution was added to

make it alkaline. NH3 distilled was separated in boric acid of volume 10 ml with

mixed indicator. The distillate was titrated against 0.01 M hydrochloric acid

(HCl) to determine total N.

To make boric acid mixed indicator solution, 20 g of boric acid was dissolved

in distilled water (980 ml) plus mixed indicator solution (20 ml). Mixed

indicator solution was prepared by dissolving bromocresol green (0.1 g) and

methyl red (0.07 g) in 95% ethanol (100 ml).

The N content was determined by applying the formula given below:

VgsampleofWeigth

DNBSN

X

XXXX

)(

100014.0)(%

*

Where,

S = Volume of standard acid used for sample titration.

B = Volume of standard acid used for blank titration.

N = Normality of the acid.

D = Sample dilution after digestion.

V = (ml) of the digest taken for distillation after dilution.

* = 0.014 is the meq. wt. of nitrogen

(% crude protein = %N x 6.25)

41

3.11.5 The effects of the integration of humic acid with nitrogen on soil properties

3.11.5.1 Soil phosphorous content (mg kg-1) at maize harvest

P (AB-DTPA extractable) was determined by the procedure described by

Soltanpour and Schwab (1977) using spectrophotometer.

3.11.5.2 Soil nitrogen content (%) at maize harvest

A known weight of oven dry soil (0.5 g) was taken at maize harvest and N

content (%) was determined by the Bremner and Mulvaney (1982) method,

which is known as Kjeldahl method.

3.11.5.3 Soil organic matter (%) at maize harvest

Soil OM content was estimated form the weight loss on ignition (Ball, 1964).

The soil samples taken were first oven dried at 105 0C for 24 hr and then ignited

in a muffle furnace at 400 0C (taken in crucibles) for 24 hr. Samples were

allowed to cool in a desiccator before the final weight recorded. The organic

matter content was calculated as follow:

100)(

)()(% X

gweightsoildryOven

gweighsoilIgnitedgweightsoildryOvenOM

3.11.6 Economic analysis of the integration of humic acid with nitrogen

The data regarding economic analysis of maize genotypes were recorded on the

basis of current market prices of inputs and agronomic practices (Boehlje and

Eidman, 1984). This procedure consists on the cost of production, gross income,

net income and value cost ratio (VCR) for a particular treatment. Prevailing

market rates were also used for calculating the values of grains and stovers of

maize genotypes. Moreover, the VCR was calculated by dividing the value of

additional yield by the cost of N fertilizer and humic acid.

3.12 Data Analysis

The statistical analysis was done according to the procedure appropriate for

RCB design having split split plot management. It was carried out using Statistix

8.1 statistical software. The means of genotypes, HA and N were compared

using LSD test at 5 % level of probability (Jan et al., 2009).

42

4. RESULTS



4.1.1 Days to emergence

Statistical analysis of the data revealed that days to emergence varied

considerably among maize genotypes whereas there was no significant difference in

days to emergence for humic acid and nitrogen levels (Table 1). None of the interaction

was found significant. The effect of year as a source of variance was also found non

significant. Maize hybrid 55w65 took more days to emergence (5.48 d), followed by

the hybrid 3025 (5.26 d) which was at par with OPV Jalal (5.21 d) while early

emergence (5.1 d) occurred in OPV Iqbal.

4.1.2 Days to 50% tasseling

Significant differences were recorded among maize genotypes, N levels, HA

and years for days to 50% tasseling (Table 2). The interactions of N×HA and N×G were

found significant. Maximum days to 50% tasseling were taken by genotype 55w65

(63.47 d), followed by 3025 (60.58 d) and Jalal (59.17 d), while Iqbal genotype took

minimum days to 50% tasseling (52.38 d). Likewise, days to 50% tasseling decreased

as HA application rate increased. More days to 50% tasseling (61.01 d) were recorded

in control plots of humic acid while 1.8 kg ha-1 HA resulted in minimum number of

days to 50% tasseling (57.29 d). Similarly, N application decreased the number of days

to 50% tasseling as its level enhanced from 0 to 240 kg ha-1. Nitrogen at 240 kg ha-1

took minimum days to tasseling (56.80 d), followed by 180 kg N ha-1 (57.74 d) while

maximum days were recorded in control plots of N (61.45 d).

The interaction of N×HA exhibited the significant response of N levels to humic

acid application regarding days to 50% tasseling in maize genotypes. Plots treated with

240 kg ha-1 N showed higher response in comparison to other N levels (Fig. 2a). The

interaction N×G indicated that with the increase in N levels the maize genotypes got

earlier 50% tasseling. The response of maize genotype Iqbal was higher in comparison

to other maize genotypes (Fig. 2b).

43

Table 1. The effect of humic acid and nitrogen on days to emergence of maize

genotypes

Mean Table 2014 2015 Two years average

Genotypes

3025 5.25 b 5.27 b 5.26 b

55w65 5.38 a 5.58 a 5.48 a

Jalal 5.24 b 5.19 b 5.22 b

Iqbal 5.17 b 5.10 b 5.14 c

LSD(0.05) 0.07 0.13 0.07

SE 0.03 0.05 0.03

Humic acid (kg ha-1)

0 5.27 5.29 5.28

0.6 5.27 5.35 5.31

1.2 5.27 5.29 5.28

1.8 5.23 5.21 5.22

LSD(0.05) 0.14 0.15 0.10

SE 0.07 0.07 0.05

Nitrogen (kg ha-1)

0 5.25 5.46 a 5.35

120 5.25 5.40 a 5.32

180 5.29 5.17 b 5.23

240 5.25 5.13 b 5.19

LSD(0.05) 0.20 0.17 0.13

SE 0.10 0.09 0.07

Interactions Significance level

N×HA Ns Ns Ns

N×G Ns Ns Ns

HA×G Ns Ns Ns

HA×G×N Ns Ns Ns

Means which do not have the same letters are significantly different from one another

at P < 0.05 using LSD test.

NS = Non-significant, * = Significant at 0.05 level of probability

44

Table 2. The effect of humic acid and nitrogen on days to 50% tasseling of

maize genotypes


Genotypes

3025 61.37 b 59.79 b 60.58 b

55w65 64.72 a 62.21 a 63.47 a

Jalal 59.83 c 58.50 b 59.17 c

Iqbal 53.95 d 50.79 c 52.38 d

LSD(0.05) 1.51 1.54 0.96

SE 0.62 0.63 0.44


0 62.12 a 59.90 a 61.01 a

0.6 60.14 b 58.04 b 59.09 b

1.2 59.29 c 57.10 c 58.20 c

1.8 58.33 d 56.25 d 57.29 d

LSD(0.05) 0.25 0.24 0.17

SE 0.12 0.12 0.08

Nitrogen (kg ha-1)

0 62.62 a 60.27 a 61.45 a

120 60.77 b 58.44 b 59.60 b

180 58.72 c 56.75 c 57.74 c

240 57.77 d 55.83 d 56.80 d

LSD(0.05) 0.21 0.19 0.14

SE 0.11 0.10 0.07


N×HA * * * (Fig. 2a)

N×G * * * (Fig. 2b)

HA×G Ns Ns Ns

HA×G×N Ns Ns Ns

The same category means that have the same letters are not significantly different from

one another at P < 0.05 using LSD test.


45

Figure 2a: Interaction between N×HA for days to 50% tasseling of maize. Vertical

bars represent standard error of mean in each interaction.

Figure 2b: Interaction between N×G for days to 50% tasseling of maize. Vertical bars

represent standard error of mean in each interaction.

53

55

57

59

61

63

65

0 0.6 1.2 1.8

Da

ys

to 5

0 %

ta

sseli

ng


N×HA

0

120

180

240

48

54

60

66

72

78

0 120 180 240

Days

to 5

0 %

tass

elin

g

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

46

4.1.3 Days to 50% silking

Statistical perusal of the data showed that humic acid, nitrogen and maize

genotypes significantly influenced the number of days to 50% silking (Table 3). The

N×HA and N×G interactions were found significant. The impact of years was also

significant as a source of variation. More days to silking were counted in the genotype

55w65 (67.16 d), followed by 3025 (63.94 d) which was at par with Jalal variety (62.40

d) while Iqbal variety resulted in fewer days to silking (55.41 d). Similarly, control plots

of humic acid took more days to 50% silking (65.09 d) while 1.8 kg HA ha-1 produced

early silking in maize (60.07 d). As expected, N application decreased number of days

to silking as its level of application increased from 0 to 240 kg ha-1. Application of N

at the rate of 240 kg ha-1 provided early silking (59.50 d), followed by 180 kg N ha-1

(60.63 d) while control plots of N resulted in late silking (65.68 d).

The interaction N×HA revealed the well response of N to humic acid application

for days to 50% silking in maize genotypes. However, 240 kg ha-1 N showed higher

response as compared to other N levels (Fig. 3a). The interaction N×G showed that with

increase in N levels the time interval required for 50% silking in maize genotypes got

reduced. Moreover, plots treated with OPV Iqbal exhibited higher response against

other maize genotypes (Fig. 3b).

4.1.4 Anthesis to silking interval (ASI)

Statistical perusal of the data revealed that genotypes, HA and N had a

significant impact on number of days from anthesis to silking (ASI) in maize (Table 4).

All interactions except N×HA were observed to be non significant. The effect of years

was recorded to be non significant as a source of variation. The maximum ASI was

found in plots treated with maize genotype 55w65 (3.69 d), followed by maize

genotypes 3025 and Jalal (3.34 d and 3.22 d respectively) while minimum ASI was

recorded in Iqbal cultivar (3.01 d). Likewise, higher ASI was observed in control plots

of humic acid (4.06 d), followed by 0.6 kg HA ha-1 (3.39 d) while lower ASI was noted

at 1.8 kg HA ha-1 (2.81 d). Regarding N, the ASI was higher in control plots (4.21 d),

followed by N application level of 120 kg ha-1 (3.48 d) while 240 kg ha-1 N resulted in

lower ASI (2.68 d).

The interaction of N×HA indicated the linear response of N nutrient to the

applications of humic acid regarding ASI of maize genotypes. The plots supplied with

47

240 kg ha-1 N showed well response in comparison to other N levels against HA

application rates (Fig. 4a).

Table 3. The effect of humic acid and nitrogen on days to 50% silking of

maize genotypes


Genotypes

3025 64.79 b 63.08 b 63.94 b

55w65 68.56 a 65.75 a 67.16 a

Jalal 63.17 c 61.63 b 62.40 b

Iqbal 57.17 d 53.65 c 55.41 c

LSD(0.05) 1.52 1.71 1.02

SE 0.62 0.70 0.47


0 66.40 a 63.79 a 65.09 a

0.6 63.69 b 61.35 b 62.52 b

1.2 62.47 c 59.94 c 61.21 c

1.8 61.12 d 59.02 d 60.07 d

LSD(0.05) 0.37 0.26 0.22

SE 0.18 0.13 0.11

Nitrogen (kg ha-1)

0 66.90 a 64.46 a 65.68 a

120 64.40 b 61.79 b 63.09 b

180 61.75 c 59.50 c 60.63 c

240 60.64 d 58.35 d 59.50 d

LSD(0.05) 0.27 0.23 0.18

SE 0.14 0.12 0.09


N×HA Ns * * (Fig. 3a)

N×G * Ns * (Fig. 3b)

HA×G Ns Ns Ns

HA×G×N Ns Ns Ns

The same category means which have different letters are significantly different from



48

Table 4. The effect of humic acid and nitrogen on anthesis to silking interval

(ASI) of maize genotypes


Genotypes

3025 3.46 b 3.23 b 3.34 b

55w65 3.83 a 3.54 a 3.69 a

Jalal 3.31 bc 3.13 bc 3.22 b

Iqbal 3.17 c 2.85 c 3.01 c

LSD(0.05) 0.23 0.29 0.17

SE 0.10 0.12 0.08


0 4.25 a 3.88 a 4.06 a

0.6 3.50 b 3.27 b 3.39 b

1.2 3.17 c 2.83 c 3.00 c

1.8 2.85 d 2.77 c 2.81 d

LSD(0.05) 0.18 0.14 0.11

SE 0.09 0.07 0.06

Nitrogen (kg ha-1)

0 4.25 a 4.17 a 4.21 a

120 3.65 b 3.31 b 3.48 b

180 3.04 c 2.75 c 2.90 c

240 2.83 d 2.52 d 2.68 d

LSD(0.05) 0.15 0.14 0.10

SE 0.07 0.07 0.05


N×HA Ns Ns * (Fig. 4a)

N×G Ns Ns Ns

HA×G Ns Ns Ns

HA×G×N Ns Ns Ns


one another at P < 0.05 using LSD, test.


49

Figure 3a: Interaction between N×HA for days to 50% silking of maize. Vertical bars


Figure 3b: Interaction between N×G for days to 50% silking of maize. Vertical bars


Figure 4a: Interaction between N×HA for anthesis to silking interval (ASI) of maize.

Vertical bars represent standard error of mean in each interaction.

55

58

61

64

67

70

73

0 0.6 1.2 1.8

Da

ys

to 5

0 %

sil

kin

g


N×HA

0

120

180

240

50

55

60

65

70

75

0 120 180 240

Days

to 5

0 %

sil

kin

g

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

1.8

2.7

3.6

4.5

5.4

6.3

0 0.6 1.2 1.8

An

thes

is t

o s

ilk

ing

in

terv

al

(AS

I)


N×HA

0

120

180

240

50

4.1.5 Days to maturity

Statistical data analysis showed that the effect of genotypes, humic acid,

nitrogen and years was significant on days to maturity of maize (Table 5). All

interactions except N×HA×G were significant. Genotype 55w65 took more days to

maturity (102.17 d), followed by 3025 (94.23 d) while early maturity was observed in

OPV Iqbal (81.21 d). Furthermore, HA application delayed the physiological maturity

and late maturity was calculated in the plots supplied with 1.8 kg HA ha-1 (93.68 d),

followed by 1.2 kg HA ha-1 (92.78 d) while early maturity was observed in plots treated

with no humic acid (90.29 d). Similarly as N level enhanced from 0 to 240 kg ha-1, days

to maturity also increased. Nitrogen application of 240 kg ha-1 took more days to

maturity (94.42 d), followed by N addition at the rate of 180 kg ha-1 (93.27 d) while

control plots of N resulted in minimum days to maturity (89.47 d).

The interaction N×HA exhibited the significant relationship among these

components for days to maturity of maize genotypes. However, the plots treated with

240 kg ha-1 N attained their physiological maturity later as compared to other N levels

(Fig. 5a). The interaction N×G showed that with the increase in level of N fertilizer the

physiological maturity of maize plants got delayed. More days were recorded for 55w65

as compared to other genotypes (Fig. 5b). The interaction of HA×G indicated that the

maturity duration of maize genotypes got lengthened with the increase in the amount

of humic acid. The response of maize hybrid 55w65 was higher as compared to other

genotypes (Fig. 5c).

4.1.6 Seed fill duration (SFD)

Statistical perusal of the data indicated that genotypes, humic acid, nitrogen and

years significantly influenced the seed fill duration (SFD) of maize (Table 6). The

interactions of G×N and HA×N were highly significant while G×HA and N×HA×G

interactions were non significant. Regarding genotypes, 55w65 took more days for SFD

(35.01 d), followed by 3025 (30.28 d) while Iqbal variety took less days in SFD (25.81

d). Furthermore, HA application at the rate of 1.8 kg ha-1 showed more SFD (33.65 d),

followed by HA application at the rate of 1.2 kg ha-1 (31.59 d) while control plots of

humic acid exhibited less SFD (25.19 d). Furthermore, N addition at the rate of 240 kg

ha-1 resulted in more days in SFD (34.32 d), followed by N use at the rate of 180 kg ha-

1 (32.66 d) while control plots of N took less number of days in SFD (23.80 d).

51

The interaction of N×HA proved the significant impact of humic acid

application on N nutrient regarding SFD of maize genotypes. Plots supplied with 240

kg ha-1 N exhibited greater response to HA application in comparison to other

treatments of N. (Fig. 6a). The interaction N×G revealed that with higher levels of N

treatments the SFD of maize genotypes increased. However, higher response was

observed in plots treated with maize hybrid 55w65 against other genotypes (Fig. 6b).

The interaction HA×G suggested that with increase in humic acid levels the SFD of

maize genotypes increased. Moreover, higher response was observed in plots treated

with hybrid 55w65 as compared to other maize genotypes (Fig. 6c).

52

Table 5. The effect of humic acid and nitrogen on days to physiological

maturity of maize genotypes


Genotypes

3025 93.29 b 95.17 b 94.23 b

55w65 99.63 a 104.71 a 102.17 a

Jalal 90.73 c 91.25 c 90.99 c

Iqbal 80.63 d 81.79 d 81.21 d

LSD(0.05) 2.33 1.14 1.15

SE 0.95 0.47 0.53


0 89.10 d 91.48 d 90.29 d

0.6 90.77 c 92.92 c 91.84 c

1.2 91.73 b 93.83 b 92.78 b

1.8 92.67 a 94.69 a 93.68 a

LSD(0.05) 0.45 0.39 0.29

SE 0.22 0.19 0.14

Nitrogen (kg ha-1)

0 88.25 d 90.69 d 89.47 d

120 90.10 c 92.77 c 91.44 c

180 92.31 c 94.23 b 93.27 b

240 93.60 a 95.23 a 94.42 a

LSD(0.05) 0.22 0.26 0.17

SE 0.11 0.13 0.09


N×HA * Ns * (Fig. 5a)

N×G * * * (Fig. 5b)

HA×G * * * (Fig. 5c)

HA×G×N Ns Ns Ns

The same category means followed by the same letters are not significantly different

from one another at P < 0.05 using LSD test.


53

Figure 5a: Interaction between N×HA for days to physiological maturity of maize.


Figure 5b: Interaction between N×G for days to physiological maturity of maize.


Figure 5c: Interaction between HA×G for days to physiological maturity of maize.


86

88

90

92

94

96

98

0 0.6 1.2 1.8

Da

ys

to m

atu

rity


N×HA

0

120

180

240

75

80

85

90

95

100

105

110

0 120 180 240

Days

to m

atu

rity

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

75

80

85

90

95

100

105

110

0 0.6 1.2 1.8

Da

ys

to m

atu

rity


HA×G

3025

55w65

Jalal

Iqbal

54

Table 6. The effect of humic acid and nitrogen on seed fill duration (SFD) of

maize genotypes


Genotypes

3025 28.48 b 32.08 b 30.28 b

55w65 31.04 a 38.98 a 35.01 a

Jalal 27.63 b 29.65 c 28.64 c

Iqbal 23.48 c 28.15 c 25.81 d

LSD(0.05) 1.86 1.51 1.07

SE 0.76 0.62 0.49


0 22.71 d 27.67 d 25.19 d

0.6 27.04 c 31.58 c 29.31 c

1.2 29.29 b 33.90 b 31.59 b

1.8 31.58 a 35.71 a 33.65 a

LSD(0.05) 0.61 0.49 0.38

SE 0.29 0.24 0.19

Nitrogen (kg ha-1)

0 21.35 d 26.25 d 23.80 d

120 25.75 c 30.98 c 28.36 c

180 30.56 b 34.75 b 32.66 b

240 32.96 a 36.88 a 34.92 a

LSD(0.05) 0.30 0.32 0.22

SE 0.15 0.16 0.11


N×HA * * * (Fig. 6a)

N×G * Ns * (Fig. 6b)

HA×G * Ns * (Fig. 6c)

HA×G×N Ns Ns Ns




55

Figure 6a: Interaction between N×HA for seed fill duration (SFD) of maize. Vertical


Figure 6b: Interaction between N×G for seed fill duration (SFD) of maize. Vertical


Figure 6c: Interaction between HA×G for seed fill duration (SFD) of maize.


16

21

26

31

36

41

46

0 0.6 1.2 1.8

See

d f

ill d

ura

tion

(S

FD

)


N×HA

0

120

180

240

16

21

26

31

36

41

46

0 120 180 240

See

d f

ill d

ura

tion

(S

FD

)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

18

23

28

33

38

43

0 0.6 1.2 1.8

See

d f

ill d

ura

tio

n (

SF

D)


HA×G

3025

55w65

Jalal

Iqbal

56


of maize genotypes

4.2.1 Total weight plant-1 at silking

Statistical perusal of the data revealed that genotypes, HA and N application

rate had a significant impact on total weight plant-1 of maize (Table 7). The N×HA and

N×G interactions were found to be significant. Years as a source of variation

significantly affected total weight plant-1 at silking. Highest total weight plant-1 was

observed in plots sown with 55w65 genotype (139.17 g), followed by 3025 (112.83 g)

while lower total weight plant-1 was produced by Iqbal variety (94.84 g). Moreover,

HA application at the rate of 1.8 kg ha-1 produced more total weight plant-1 (118.90 g),

followed by HA application at the rate of 1.2 kg ha-1 (115.58 g) while HA application

at the rate of 0 kg ha-1 provided less total weight plant-1 (108.47 g). Similarly, total

weight plant-1 was higher in plots treated with 240 kg ha-1 N (134.54 g), followed by N

application level of 180 kg ha-1 (122.96 g) while control plots of N (0 kg N ha-1) resulted

in lower total weight plant-1 (89.39 g).

The interaction of N×HA showed that N fertilizer responded in a substantial

manner to the increased levels of humic acid with respect to the total weight plant-1 in

maize genotypes. Moreover, 240 kg N ha-1 exhibited more response as compared to

other N levels (Fig. 7a). The interaction N×G revealed the well response of maize

genotypes regarding total weight plant-1 at silking to higher levels of N fertilization.

However, greater response was shown by maize hybrid 55w65 as compared to other

genotypes (Fig. 7b). The interaction of HA×G indicated that maize genotypes

responded considerably to higher levels of humic acid in terms of total weight plant-1.

Moreover, heavier plants were observed in plots treated with hybrid 55w65 against

other genotypes (Fig. 7c).

4.2.2 Ear weight plant-1 at silking

Statistical analysis of the data showed that genotypes, humic acid, nitrogen and

years significantly affected ear weight plant-1 of maize at silking stage (Table 8). None

of the interaction was significant except N x G. More ear weight at silking of maize was

recorded by 55w65 genotype (32.03 g), followed by 3025 (27.54 g) while Iqbal variety

resulted in lower ear weight plant-1 at silking of maize (21.85 g). Likewise, HA

application linearly increased ear weight plant-1 at silking. More ear weight at silking

57

was recorded by plots treated with 1.8 kg HA ha-1 (28.36 g), followed by 1.2 kg HA ha-

1 (27.31 g) while control plots of humic acid produced lower ear weight plant-1 at silking

of maize (25.15 g). Moreover, ear weight at silking of maize improved as N application

level enhanced from 0 to 240 kg ha-1. More ear weight plant-1 at silking of maize was

reported in experimental untis treated with 240 kg ha-1 N (33.36 g), followed by N

application level of 180 kg ha-1 (29.34 g) while lower ear weight at silking was observed

in control plots of N (19.52 g).

The interaction N×G exhibited the well response of maize genotypes for ear

weight plant-1 at silking to different levels of N fertilizer. However, greater response

was exhibited by hybrid 55w65 as compared to other maize genotypes (Fig. 8a).

58

Table 7. The effect of humic acid and nitrogen on total weight (g) plant-1 at

silking stage of maize genotypes


Genotypes

3025 111.10 b 114.56 b 112.83 b

55w65 135.97 a 142.37 a 139.17 a

Jalal 107.19 c 108.73 c 107.96 c

Iqbal 91.82 d 97.86 d 94.84 d

LSD(0.05) 2.31 5.36 2.60

SE 0.95 2.19 1.19


0 106.43 d 110.50 d 108.47 d

0.6 109.84 c 113.88 c 111.86 c

1.2 113.46 b 117.69 b 115.58 b

1.8 116.35 a 121.45 a 118.90 a

LSD(0.05) 1.09 1.65 0.96

SE 0.53 0.80 0.48

Nitrogen (kg ha-1)

0 87.07 d 91.71 d 89.39 d

120 105.31 c 110.52 c 107.92 c

180 120.60 b 125.32 b 122.96 b

240 133.11 a 135.97 a 134.54 a

LSD(0.05) 0.42 0.49 0.32

SE 0.21 0.25 0.16


N×HA * * * (Fig.7a)

N×G * * * (Fig. 7b)

HA×G * * * (Fig. 7c)

HA×G×N Ns Ns Ns

The same category means which have the same letters are not significantly different



59

Table 8. The effect of humic acid and nitrogen on ear weight (g) plant-1 at



Genotypes

3025 26.23 b 28.84 b 27.54 b

55w65 31.12 a 32.94 a 32.03 a

Jalal 24.71 c 26.60 c 25.66 c

Iqbal 20.68 d 23.02 d 21.85 d

LSD(0.05) 1.23 0.58 0.60

SE 0.50 0.24 0.28


0 24.03 d 26.26 d 25.15 d

0.6 25.15 c 27.37 c 26.26 c

1.2 26.22 b 28.39 b 27.31 b

1.8 27.34 a 29.38 a 28.36 a

LSD(0.05) 0.37 0.68 0.38

SE 0.18 0.33 0.19

Nitrogen (kg ha-1)

0 18.40 d 20.63 d 19.52 d

120 23.80 c 25.91 c 24.85 c

180 28.28 b 30.40 b 29.34 b

240 32.25 a 34.47 a 33.36 a

LSD(0.05) 0.14 0.15 0.10

SE 0.07 0.08 0.05


N×HA * Ns Ns

N×G * Ns * (Fig. 8a)

HA×G Ns Ns Ns

HA×G×N Ns Ns Ns




60

Figure 7a: Interaction between N×HA for total weight (g) plant-1 of maize at

silking. Vertical bars represent standard error of mean in each

interaction.

Figure 7b: Interaction between N×G for total weight (g) plant-1 of maize at silking.


75

85

95

105

115

125

135

145

155

0 0.6 1.2 1.8

To

tal

wei

gh

t (g

) p

lan

t-1a

t si

lkin

g


N×HA

0

120

180

240

60

80

100

120

140

160

180

200

0 120 180 240

To

tal

wei

gh

t (g

) p

lan

t-1at

silk

ing

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

61

Figure 7c: Interaction between HA×G for total weight (g) plant-1 of maize at

silking. Vertical bars represent standard error of mean in each

interaction.

Figure 8a: Interaction between N×G for ear weight (g) plant-1 of maize at silking.


80

90

100

110

120

130

140

150

160

0 0.6 1.2 1.8

To

tal

wei

gh

t (g

) p

lan

t-1a

t si

lkin

g


HA×G

3025

55w65

Jalal

Iqbal

10

15

20

25

30

35

40

45

0 120 180 240

Ea

r w

eigh

t (g

) p

lan

t-1at

silk

ing

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

62

4.2.3 Plant height (cm)

Statistical analysis of the data indicated that genotypes, humic acid, nitrogen

and years appreciably impacted maize plant height (Table 9). The interactions of N×G

and N×HA were found significant. The genotype 55w65 produced taller plants (231.63

cm), followed by 3025 (220.28 cm) while Iqbal variety resulted in short stature plants

(193.61 cm). Additionally, for HA applications, greater plant height was found in plots

treated with HA at the rate of 1.8 kg ha-1 (217.10 cm), followed by HA application of

1.2 kg ha-1 (215.47 cm) while it was lower under control plots of HA application

(212.04 cm). Regarding N application rates, plant height showed an enhancement by

increasing N application level from 0 to 240 kg ha-1. Nitrogen application at the rate of

240 kg ha-1 produced taller plants (225.59 cm), followed by 180 kg ha-1 N (220.13 cm)

while control plots of N (0 kg N ha-1) resulted in plants of lower height (200.61 cm).

The interaction N×G revealed that all genotypes were highly responsive to the

applications of N levels as far as plant height is concerned (Fig. 9a). The hybrid 55w65

proved to be more responsive to the N application levels against other maize genotypes.

The interaction N×G exhibited that height of different maize genotypes enhanced with

increasing N levels in a significant way. However, the plots treated with hybrid 3025

and 55w65 provided the tallest plants in comparison to other genotypes in response to

N application (Fig. 9b).

63

Table 9. The effect of humic acid and nitrogen on plant height (cm) of maize

genotypes


Genotypes

3025 218.38 b 222.19 b 220.28 b

55w65 228.64 a 234.62 a 231.63 a

Jalal 208.51 c 217.14 c 212.83 c

Iqbal 191.20 d 196.03 d 193.61 d

LSD(0.05) 1.97 1.59 1.13

SE 0.80 0.65 0.52


0 209.21 d 214.87 d 212.04 d

0.6 210.95 c 216.55 c 213.75 c

1.2 212.47 b 218.46 b 215.47 b

1.8 214.10 a 220.10 a 217.10 a

LSD(0.05) 0.98 1.04 0.70

SE 0.48 0.50 0.35

Nitrogen (kg ha-1)

0 197.16 d 204.07 d 200.61 d

120 208.71 c 215.33 c 212.02 c

180 217.23 b 223.03 b 220.13 b

240 223.63 a 227.55 a 225.59 a

LSD(0.05) 0.43 0.31 0.26

SE 0.22 0.16 0.13


N×HA Ns Ns Ns

N×G * * * (Fig. 9a)

HA×G * * * (Fig. 9b)

HA×G×N Ns Ns Ns




64

Figure 9a: Interaction between N×G for plant height (cm) of maize at maturity.


Figure 9b: Interaction between HA×G for plant height (cm) of maize at maturity.


170

190

210

230

250

270

0 120 180 240

Pla

nt

hei

gh

t (c

m)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

180

195

210

225

240

0 0.6 1.2 1.8

Pla

nt

hei

gh

t (c

m)


HA×G

3025

55w65

Jalal

Iqbal

65

4.2.4 Absolute growth rate (AGR) at silking

Statistical analysis indicated that genotypes, HA and N application rate

significantly affected absolute growth rate (AGR) of maize at silking (Table 10). The

interactions N×HA, N×G and HA×G interactions were found significant. The effect of

years was also significant as a source of variation. The hybrid 55w65 resulted in higher

AGR (2.10 g plant-1 day-1), followed by 3025 (1.78 g plant-1 day-1) which was at par

with Jalal and Iqbal varieties (1.75 and 1.74 g plant-1 day-1 respectively). Similarly,

higher AGR was calculated in plots treated with 1.8 kg ha-1 HA (1.99 g plant-1 day-1),

followed by humic acid application at the rate of 1.2 kg ha-1 (1.90 g plant-1 day-1) while

control plots resulted in lower AGR (1.67 g plant-1 day-1). Nitrogen application

increased AGR in linear fashion and higher AGR was recorded in the experimental

units treated with 240 kg ha-1 N (2.26 g plant-1 day-1), followed by the plots supplied

with 180 kg ha-1 N (2.04 g plant-1 day-1) while control plots (0 kg N ha-1) produced

lower AGR (1.36 g plant-1 day-1).

The interaction N×HA indicated the well response of N nutrient to the increase

in application levels of humic acid regarding AGR of maize genotypes at phenological

stage of silking. However, the plots supplied with 180 and 240 kg ha-1 N responded

well as compared to other N levels (Fig. 10a). The interaction of N×G showed the linear

response of maize genotypes to the addition of N fertilizer with respect to AGR at

silking. In this regard the trend of maize hybrid 55w65 was higher against other maize

genotypes (Fig. 10b). The interaction of HA×G exhibited the significant influence of

humic acid on AGR of maize genotypes up to silking stage. The response of 55w65

was greater in comparison to other genotypes (Fig. 10c).

4.2.5 Crop growth rate (CGR) at silking

Statistical perusal of the data suggested that genotypes, humic acid, nitrogen

and years considerably affected maize CGR at silking (Table 11). The N×HA, N×G and

G×HA interactions were significant. Regarding maize genotypes, 55w65 resulted in

higher AGR (14.40 g m-2 day-1), followed by 3025 (12.50 g m-2 day-1) which was at par

with OPVs Jalal and Iqbal (12.22 and 12.15 g m-2 day-1 respectively). Humic acid

application increased CGR in a linear fashion and higher CGR was calculated in plots

treated with 1.8 kg ha-1 HA (13.84 g m-2 day-1), followed by 1.2 kg ha-1 HA (13.21 g m-

2 day-1) while no HA treated plots (0 kg HA ha-1) resulted in lower CGR (11.67 g m-2

66

day-1). Moreover, CGR observed was greater in plots treated with 240 kg N ha-1 (15.74

g m-2 day-1), followed by 180 kg ha-1 N (14.19 g m-2 day-1) while control plots of N

resulted in lower CGR (9.50 g m-2 day-1) of maize plants.

The interaction of N×HA exhibited the linear relationship among humic acid

levels and N fertilization for CGR of maize plants at silking in all the genotypes. The

plots treated with 180 and 240 kg ha-1 N revealed substantial response in comparison

to other N rates (Fig. 11a). The interaction of N×G showed the linear response of maize

genotypes to enhanced levels of N fertilization for CGR at silking stage of crop growth.

The genotypes 55w65 and 3025 indicated higher response when compared with other

cultivars (Fig. 11b). The interaction HA×G evaluated the well response among CGR of

maize genotypes and increased HA levels. However, 55w65 exhibited higher response

in comparison to other maize genotypes (Fig. 11c).

67

Table 10. The effect of humic acid and nitrogen on AGR (g plant-1 day-1) of

maize genotypes at silking


Genotypes

3025 1.73 b 1.83 b 1.78 b

55w65 2.01 a 2.18 a 2.10 a

Jalal 1.72 b 1.78 b 1.75 b

Iqbal 1.64 c 1.84 b 1.74 b

LSD(0.05) 0.06 0.10 0.05

SE 0.03 0.04 0.02


0 1.61 d 1.74 d 1.67 d

0.6 1.74 c 1.86 c 1.80 c

1.2 1.83 b 1.97 b 1.90 b

1.8 1.92 a 2.06 a 1.99 a

LSD(0.05) 0.02 0.03 0.02

SE 0.01 0.02 0.01

Nitrogen (kg ha-1)

0 1.30 d 1.41 c 1.36 d

120 1.63 c 1.79 bc 1.71 c

180 1.97 b 2.11 b 2.04 b

240 2.19 a 2.33 a 2.26 a

LSD(0.05) 0.01 0.01 0.01

SE 0.01 0.01 0.01


N×HA * * * (Fig. 10a)

N×G * * * (Fig. 10b)

HA×G Ns * * (Fig. 10c)

HA×G×N Ns Ns Ns




68

Figure 10a: Interaction between N×HA for AGR (g plant-1 day-1) of maize at silking.


Figure 10b: Interaction between N×G for AGR (g plant-1 day-1) of maize at silking.


Figure 10c: Interaction between HA×G for AGR (g plant-1 day-1) of maize at silking.


1.1

1.5

1.9

2.3

2.7

0 0.6 1.2 1.8

Ab

solu

te g

row

th r

ate

(A

GR

)

at

silk

ing


N×HA

0

120

180

240

1.0

1.4

1.8

2.2

2.6

3.0

0 120 180 240

Ab

solu

te g

row

th r

ate

(A

GR

)

at

silk

ing

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

1.4

1.6

1.8

2.0

2.2

2.4

0 0.6 1.2 1.8

Ab

solu

te g

row

th r

ate

(A

GR

)

at

silk

ing


HA×G

3025

55w65

Jalal

Iqbal

69

Table 11. The effect of humic acid and nitrogen on CGR (g m-2 day-1) of maize

genotypes at silking


Genotypes

3025 12.11 b 12.89 b 12.50 b

55w65 13.70 a 15.09 a 14.40 a

Jalal 11.92 c 12.53 b 12.22 b

Iqbal 11.41 d 12.90 b 12.15 b

LSD(0.05) 0.44 0.60 0.33

SE 0.18 0.25 0.15


0 11.17 d 12.17 d 11.67 d

0.6 12.02 c 13.06 c 12.54 c

1.2 12.65 b 13.77 b 13.21 b

1.8 13.28 a 14.40 a 13.84 a

LSD(0.05) 0.14 0.18 0.11

SE 0.07 0.09 0.06

Nitrogen (kg ha-1)

0 9.05 d 9.96 d 9.80 d

120 11.27 c 12.40 c 11.88 c

180 13.64 b 14.74 b 14.19 b

240 15.17 a 16.30 a 15.74 a

LSD(0.05) 0.08 0.11 0.07

SE 0.04 0.05 0.03


NxHA * * * (Fig. 11a)

NxG * * * (Fig. 11b)

HAxG * * * (Fig. 11c)

HAxGxN Ns Ns Ns




70

Figure 11a: Interaction between N×HA for CGR (g m-2 day-1) of maize at silking.


Figure 11b: Interaction between N×G for CGR (g m-2 day-1) of maize at silking.


Figure 11c: Interaction between HA×G for CGR (g m-2 day-1) of maize at silking.


8.0

10.0

12.0

14.0

16.0

18.0

20.0

0 0.6 1.2 1.8

Cro

p g

row

th r

ate

(C

GR

) a

t

silk

ing


N×HA

0

120

180

240

7.2

9.4

11.6

13.8

16.0

18.2

20.4

0 120 180 240Cro

p g

row

th r

ate

(C

GR

) at

silk

ing

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

10.0

11.5

13.0

14.5

16.0

17.5

0 0.6 1.2 1.8Cro

p g

row

th r

ate

(C

GR

) at

silk

ing


HA×G

3025

55w65

Jalal

Iqbal

71

4.2.6 Total weight plant-1 at maturity

Statistical perusal of the data revealed that genotypes, humic acid, nitrogen and

years appreciably affected total weight plant-1 at maturity (Table 12). The N×HA, N×G

and HA×G interactions were found to be significant. Higher total weight plant-1 was

recorded for hybrid 55w65 (274.83 g), followed by 3025 (255.28 g) while OPV Iqbal

resulted in lower total weight plant-1 (186.90 g). Similarly, total weight plant-1 was

higher in plots treated with HA at the rate of 1.8 kg ha-1 (242.88 g), followed by HA

application of 1.2 kg ha-1 (236.76 g) while total weight plant-1 was lower in plots

without HA (221.63 g). Likewise, N application increased total weight plant-1 as its

application level increased from 0 to 260 kg ha-1. Application of N at the rate of 240 kg

ha-1 produced more total weight plant-1 (277.25 g), followed by N application level of

180 kg ha-1 (252.02 g) while plots without N (control) produced lower total weight

plant-1 (179.22 g).

The interaction N×HA showed the synergistic impact of humic acid on N

fertilizer regarding total weight plant-1 of maize genotypes. Moreover, the treatments

supplied with 240 kg ha-1 N showed greater response when compared with the

remaining N levels (Fig. 12a). The interaction of N×G proved the linear response of

maize genotypes to N levels regarding total weight plant-1 at maturity. However, the

response was greater for hybrid 55w65 in comparison to other maize genotypes (Fig.

12b). The interaction HA×G indicated the linear response of maize genotypes to the

increase of humic acid regarding the total weight plant-1. The OPVs Jalal and Iqbal

proved to be more responsive than other maize genotypes (Fig. 12c).

72

Table 12. The effect of humic acid and nitrogen on total weight (g) plant-1 of

maize genotypes at maturity


Genotypes

3025 253.75 b 256.80 b 255.28 b

55w65 273.29 a 276.38 a 274.83 a

Jalal 210.30 c 213.41 c 211.86 c

Iqbal 184.77 d 189.02 d 186.90 d

LSD(0.05) 2.08 3.42 1.78

SE 0.85 1.40 0.82


0 220.21 d 222.20 d 221.20 d

0.6 226.64 c 227.94 c 227.29 c

1.2 233.51 b 238.91 b 236.21 b

1.8 240.21 a 244.65 a 242.43 a

LSD(0.05) 0.91 6.36 3.13

SE 0.44 3.08 1.56

Nitrogen (kg ha-1)

0 176.72 d 181.71 d 179.22 d

120 219.89 c 220.85 c 220.37 c

180 250.30 b 250.29 b 250.29 b

240 273.66 a 280.83 a 277.25 a

LSD(0.05) 0.72 5.73 2.87

SE 0.36 2.89 1.45



N×G * * * (Fig. 12b)

HA×G * * * (Fig. 12c)

HA×G×N * Ns Ns




73

Figure 12a: Interaction between N×HA for total weight (g) plant-1 of maize at

maturity. Vertical bars represent standard error of mean in each

interaction.

Figure 12b: Interaction between N×G for total weight (g) plant-1 of maize at


interaction.

Figure 12c: Interaction between HA×G for total weight (g) plant-1 of maize at


interaction.

150

190

230

270

310

0 0.6 1.2 1.8

To

tal

wei

gh

t (g

) p

lan

t-1a

t

ma

turi

ty


N×HA

0

120

180

240

120

170

220

270

320

370

0 120 180 240

Tota

l w

eigh

t (g

) p

lan

t-1at

matu

rity

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

160

200

240

280

320

0 0.6 1.2 1.8

To

tal

wei

gh

t (g

) p

lan

t-1at

ma

turi

ty


HA×G

3025

55w65

Jalal

Iqbal

74

4.2.7 AGR at maturity

Statistical perusal of the data showed that genotypes, humic acid, nitrogen and

years notably affected AGR of maize at maturity as indicated in Table 13. The

interactions of N×HA and N×G were found significant. While considering genotypes,

more AGR was recorded for 3025 and 55w65 (2.70 and 2.68 g plant-1 day-1) while the

lower AGR was observed for Jalal and Iqbal genotypes of maize (2.32 and 2.29 g plant-

1 day-1). In case of humic acid treatments, the AGR was higher in those plots which

received HA at the rate of 1.8 kg ha-1 (2.57 g plant-1 day-1), followed by 1.2 kg HA ha-

1 (2.53 g plant-1 day-1) while it was lower in control plots of humic acid (2.44 g plant-1

day-1). Nitrogen application increased AGR of maize in a linear way. AGR value was

higher in plots supplied with 240 kg ha-1 N (2.92 g plant-1 day-1), followed by N use at

the rate of 180 kg ha-1 (2.69 g plant-1 day-1) while control plots resulted in lower AGR

of maize plants (1.99 g plant-1 day-1).

The interaction N×HA indicated the well response of N fertilizer to the additions

of humic acid with respect to the AGR of maize genotypes at maturity. However, the

plots treated with 180 and 240 kg ha-1 N showed more consistent response to the

successive applications of humic acid as compared to other N levels (Fig. 13a). The

interaction of N×G exhibited the linear relationship among maize genotypes and N

levels regarding AGR of maize genotypes. Moreover, the genotypes of 55w65 and 3025

superseded OPVs of maize (Fig. 13b).

4.2.8 CGR at maturity

From the statistical analysis of the data it was found that genotypes, HA, N

levels and years substantially influenced CGR of maize at maturity (Table 14). The N

x HA and N x G interactions were found to be significant. Regarding genotypes, more

CGR was calculated for 3025 (17.91 g m-2 day-1), followed by 55w65 (17.51 g m-2 day-

1) while OPV Iqbal resulted in lower CGR (14.46 g m-2 day-1) which was at par with

Jalal (14.54 g m-2 day-1). Likewise, 1.8 kg ha-1 humic acid provided higher CGR (16.88

g m-2 day-1), followed by 1.2 kg HA ha-1 application (16.38 g m-2 day-1) while no HA

plots resulted in lower CGR (15.40 g m-2 day-1). Similarly, nitrogen application to the

sub-subplots at the rate of 240 kg ha-1 produced higher CGR (20.05 g m-2 day-1),

followed by N application at the rate of 180 kg ha-1 (17.86 g m-2 day-1) while control

plots (without N treatment) resulted in lower CGR of maize plots (11.57 g m-2 day-1).

75

The interaction of N×HA revealed that humic acid application increased the

impact of N levels on CGR of maize genotypes in a significant way. The plots

supplemented with 240 kg ha-1 N recorded notably higher CGR as compared to other

N levels (Fig. 14a). The interaction of N×G showed that maize genotypes responded

positively to various levels of N fertilization. Moreover, the plots sown with hybrid

55w65 markedly produced higher CGR in comparison to other maize genotypes (Fig.

14b).

76

Table 13. The effect of humic acid and nitrogen on AGR (g plant-1 day-1) of



Genotypes

3025 2.71 a 2.69 a 2.70 a

55w65 2.73 a 2.63 b 2.68 a

Jalal 2.31 b 2.33 c 2.32 b

Iqbal 2.29 b 2.30 c 2.29 b

LSD(0.05) 0.07 0.05 0.04

SE 0.03 0.02 0.02


0 2.45 d 2.42 c 2.44 d

0.6 2.48 c 2.48 b 2.50 c

1.2 2.53 b 2.53 b 2.55 b

1.8 2.58 a 2.59 a 2.61 a

LSD(0.05) 0.02 0.06 0.03

SE 0.01 0.03 0.02

Nitrogen (kg ha-1)

0 2.05 d 2.04 d 2.05 d

120 2.41 c 2.39 c 2.40 c

180 2.69 b 2.68 b 2.69 b

240 2.91 a 2.93 a 2.92 a

LSD(0.05) 0.01 0.06 0.03

SE 0.01 0.03 0.01



N×G * Ns * (Fig. 13b)

HA×G Ns Ns Ns

HA×G×N * Ns Ns




77

Figure 13a: Interaction between N×HA for AGR (g plant-1 day-1) of maize at


interaction.

Figure 13b: Interaction between N×G for AGR (g plant-1 day-1) of maize at maturity.


1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

0 0.6 1.2 1.8

Ab

solu

te g

row

th r

ate

(A

GR

) a

t m

atu

rity


N×HA

0

120

180

240

1.6

1.9

2.2

2.5

2.8

3.1

3.4

3.7

0 120 180 240

Ab

solu

te g

row

th r

ate

(A

GR

) at

matu

rity

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

78

Table 14. The effect of humic acid and nitrogen on CGR (g m-2 day-1) of maize

genotypes at maturity


Genotypes

3025 17.65 a 18.17 a 17.91 a

55w65 17.53 a 17.49 b 17.51 b

Jalal 15.90 b 16.62 c 14.54 c

Iqbal 16.03 b 16.60 c 14.46 c

LSD(0.05) 0.54 0.28 0.27

SE 0.22 0.12 0.13


0 15.07 d 15.73 c 15.40 d

0.6 15.43 c 16.08 c 15.76 c

1.2 15.95 b 16.81 b 16.38 b

1.8 16.43 a 17.33 a 16.88 a

LSD(0.05) 0.14 0.45 0.23

SE 0.07 0.22 0.11

Nitrogen (kg ha-1)

0 11.05 d 12.09 d 11.57 d

120 14.64 c 15.25 c 14.94 c

180 17.56 b 18.16 b 17.86 b

240 19.63 a 20.46 a 20.05 a

LSD(0.05) 0.07 0.40 0.20

SE 0.04 0.20 0.10



N×G * Ns * (Fig. 14b)

HA×G * Ns Ns

HA×G×N Ns Ns Ns




79

Figure 14a: Interaction between N×HA for CGR (g m-2 day-1) of maize at maturity.


Figure 14b: Interaction between N×G for CGR (g m-2 day-1) of maize at maturity.


10

12

14

16

18

20

22

0 0.6 1.2 1.8

Cro

p g

row

th r

ate

(C

GR

) a

t m

atu

rity


N×HA

0

120

180

240

8

11

14

17

20

23

26

0 120 180 240

Cro

p g

row

th r

ate

(C

GR

) at

matu

rity

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

80



4.3.1 Leaves plant-1 at silking

Statistical analysis indicated that genotypes, humic acid and N application rate

considerably affected leaves number plant-1 (Table 15). The interactions of N×HA and

N×G were found to be significant. The effect of years was also found to be significant

as a source of variation. The hybrid 55w65 resulted in higher number of leaves plant-1

(13.18), followed by Jalal (12.96) while Iqbal variety resulted in lower number of leaves

plant-1 (11.80). Likewise, more leaves plant-1 (12.77) were recorded when humic acid

was applied at the rate of 1.8 kg ha-1 as compared to control plots of humic acid (12.30).

Furthermore, nitrogen application at the rate of 240 kg ha-1 produced more leaves plant-

1 (13.45), followed by 180 kg N ha-1 (12.99) while control plots of N resulted in lower

number of leaves per plant (11.41).

The interaction N×HA showed that leaves plant-1 of maize genotypes increased

with the application of N fertilizer in a linear way as humic acid has a significant impact

on N levels. However, 120 and 180 kg ha-1 N exhibited greater response as compared

to other N treatments (Fig. 15a). The interaction N×G revealed that genotypes

responded well to heavier doses of N regarding number of leaves plant-1. The higher

response was calculated for 55w65 when compared with other maize genotypes (Fig.

15b). Similarly, the interaction HA×G exhibited that the leaves plant-1 in maize

genotypes increased in a linear fashion with the increase in humic acid. The hybrids

55w65 and 3025 showed more response in comparison to other maize genotypes (Fig.

15c).

4.3.2 Leaf dry weight plant-1 at silking

Statistical perusal of the data indicated that genotypes, humic acid, N levels and

years substantially affected dry leaf weight plant-1 of maize at silking stage as given in

Table 16. The interaction of N×G was found significant. More dry leaf weight plant-1

of maize was recorded by genotype 55w65 (37.01g), followed by Jalal variety (30.67

g) while OPV Iqbal resulted in lower dry leaf weight plant-1 of maize (22.96 g).

Similarly, humic acid application linearly increased dry leaf weight of maize. More dry

leaf weight plant-1 of maize was recorded in plots treated with 1.8 kg ha-1 HA (31.16

81

g), followed by 1.2 kg ha-1 HA application (29.76 g) while plots without HA resulted

in less dry leaf weight plant-1 of maize (27.57 g). Moreover, dry leaf weight of maize

improved as N application rate enhanced from 0 to 240 kg ha-1. More dry leaf weight

plant-1 of maize was recorded in plots supplied with 240 kg N ha-1 (35.92 g), followed

by 180 kg ha-1 N (31.75 g) while lower dry leaf weight of maize was recorded in sample

collected from control plots (22.70 g).

The interaction of N×G indicated that maize genotypes responded considerably

to higher rates of N fertilization and produced heavier dry leaf weight plant-1. However,

the response was higher for 55w65 in comparison to other maize genotypes (Fig. 16a).

82

Table 15. The effect of humic acid and nitrogen on leaves plant-1 at silking

stage of maize genotypes


Genotypes

3025 11.70 c 12.64 b 12.17 c

55w65 12.75 a 13.61 a 13.18 a

Jalal 12.43 b 13.50 a 12.96 b

Iqbal 11.34 d 12.25 c 11.80 d

LSD(0.05) 0.11 0.20 0.10

SE 0.05 0.08 0.05


0 11.84 d 12.76 d 12.30 d

0.6 11.98 c 12.94 c 12.46 c

1.2 12.12 b 13.08 b 12.60 b

1.8 12.29 a 13.23 a 12.77 a

LSD(0.05) 0.07 0.08 0.05

SE 0.03 0.04 0.03

Nitrogen (kg ha-1)

0 10.86 d 11.97 d 11.41 d

120 11.80 c 12.72 c 12.26 c

180 12.55 b 13.43 b 12.99 b

240 13.01 a 13.89 a 13.45 a

LSD(0.05) 0.04 0.05 0.03

SE 0.02 0.02 0.02



N×G * * * (Fig. 15b)


HA×G×N Ns Ns Ns


from one another at P ≤ 0.05 using LSD test.


83

Table 16. The effect of humic acid and nitrogen on leaf dry weight (g) plant-1

at silking stage of maize genotypes


Genotypes

3025 25.08 c 28.60 c 26.84 c

55w65 35.48 a 38.55 a 37.01 a

Jalal 29.31 b 32.03 b 30.67 b

Iqbal 21.80 d 24.11 d 22.96 d

LSD(0.05) 1.74 1.37 0.98

SE 0.71 0.56 0.45


0 26.34 c 28.79 d 27.57 d

0.6 27.64 b 30.35 c 28.99 c

1.2 27.97 b 31.55 b 29.76 b

1.8 29.72 a 32.60 a 31.16 a

LSD(0.05) 0.99 0.50 0.54

SE 0.48 0.24 0.27

Nitrogen (kg ha-1)

0 21.46 d 23.95 d 22.70 d

120 25.68 c 28.53 c 27.10 c

180 30.27 b 33.23 b 31.75 b

240 34.25 a 37.59 a 35.92 a

LSD(0.05) 0.96 0.31 0.50

SE 0.48 0.15 0.25


N×HA Ns Ns Ns

N×G * * * (Fig. 16a)

HA×G Ns Ns Ns

HA×G×N Ns Ns Ns




84

Figure 15a: Interaction between N×HA for leaves plant-1 of maize. Vertical bars

represent standard error of mean in each interaction

Figure 15b: Interaction between N×G for leaves plant-1 of maize. Vertical bars


10.5

11.5

12.5

13.5

14.5

0 0.6 1.2 1.8

Lea

ves

pla

nt-1


N×HA

0

120

180

240

10.0

11.0

12.0

13.0

14.0

15.0

0 120 180 240

Lea

ves

pla

nt-1

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

85

Figure 15c: Interaction between HA×G for leaves plant-1 of maize. Vertical bars


Figure 16a: Interaction between N×G for leaf dry weight (g) plant-1 at silking.


11.2

11.9

12.6

13.3

14.0

0 0.6 1.2 1.8

Lea

ves

pla

nt-1


HA×G

3025

55w65

Jalal

Iqbal

14

22

30

38

46

54

0 120 180 240

Lea

f d

ry w

igh

t (g

) p

lan

t-1at

silk

ing

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

86

4.3.3 Leaf area plant-1 at silking

Statistical perusal of the data exhibited that maize genotypes, humic acid,

nitrogen and years significantly influenced leaf area plant-1 of maize at silking stage

(Table 17). The interactions N×G and HA×G were significant. Highest leaf area plant-

1 was recorded in plots sown with 55w65 genotype (6210.85 cm2), followed by OPV

Jalal (5576.42 cm2) while lower leaf area plant-1 was produced by Iqbal variety

(4767.21 cm2). Moreover, HA application at the rate of 1.8 kg ha-1 produced maximum

leaf area plant-1 (5601.24 cm2), followed by HA application at the rate of 1.2 kg ha-1

(5483.71 cm2) while control application of HA produced less leaf area plant-1 (5240.01

cm2). Moreover, higher leaf area plant-1 was recorded in plots supplied with 240 kg N

ha-1 (6139.39 cm2), followed by N application rate of 180 kg ha-1 (5683.17 cm2) while

control treatments of N provided lower leaf area plant-1 (4630.58 cm2).

The interaction of N×G exhibited the well response of maize genotypes for leaf

area plant-1 at silking to N fertilizer levels. The best response was observed for Jalal

variety of maize against other genotypes (Fig. 17a).

4.3.4 Leaf area index (LAI) at silking

Analysis of variance indicated that genotypes, humic acid, nitrogen and years

caused significant variation in leaf area index (LAI) of maize (Table 18). All the

interactions were observed to be significant. Maximum LAI was measured in plots

sown with hybrid 55w65 (4.28), followed by OPV Jalal (3.91) while genotype Iqbal

resulted in lower LAI at silking (3.35). Furthermore, humic acid application at the rate

of 1.8 kg ha-1 produced higher LAI (3.91), followed by HA application at the rate of

1.2 kg ha-1 (3.82) while no humic acid application (0 kg HA ha-1) produced lower LAI

(3.66). Likewise, N application level of 240 kg ha-1 provided more LAI (4.27) as

compared to other levels of nitrogen (3.27).

The interaction of N×HA revealed that LAI of maize plants improved linearly

with the increase in the amount of N nutrient due to well response of nitrogen for humic

acid. Moreover, the better response was observed for plots supplied with 180 and 240

kg ha-1 N as compared to other N levels (Fig. 18a). The interaction of N×G indicated

the significant impact of N fertilization on LAI of maize genotypes. The larger response

was observed for OPV Jalal against other maize genotypes, although more LAI was

measured for hybrid 55w65 (Fig. 18b). The interaction HA×G showed that LAI of

87

maize genotypes had a linear response to humic acid application. However, the OPV

Jalal responded in a better way as compared to other genotypes (Fig. 18c). The

interaction G×HA×N revealed the considerable differences among genotypes for LAI

due to N and humic acid application. LAI increased with increase in N and HA for all

genotypes. However, the application of N at 120 kg ha-1 with increasing humic acid,

markedly enhanced LAI of hybrid 3025 as compared to 55w65. The same trend was

recorded for OPV Jalal as compared to Iqbal at 180 kg N ha-1 (Fig. 18d).

88

Table 17. The effect of humic acid and nitrogen on leaf area (cm2) plant-1 at



Genotypes

3025 5062.21 c 5206.31 c 5134.26 c

55w65 6100.02 a 6321.68 a 6210.85 a

Jalal 5518.38 b 5634.50 b 5576.44 b

Iqbal 4673.00 d 4861.43 d 4767.21 d

LSD(0.05) 124.64 66.59 62.92

SE 50.94 27.21 28.88


0 5159.01 d 5321.01 d 5240.01 d

0.6 5281.00 c 5446.60 c 5363.80 c

1.2 5397.86 b 5569.56 b 5483.71 b

1.8 5515.74 a 5686.74 a 5601.24 a

LSD(0.05) 45.09 23.68 24.81

SE 21.85 11.47 12.34

Nitrogen (kg ha-1)

0 4538.58 d 4722.57 d 4630.58 d

120 5152.62 c 5318.63 c 5235.63 c

180 5599.20 b 5767.14 b 5683.17 b

240 6063.21 a 6215.56 a 6139.39 a

LSD(0.05) 40.20 14.39 21.21

SE 20.25 7.25 10.76


N×HA Ns Ns Ns

N×G * * * (Fig. 17a)

HA×G Ns * Ns

HA×G×N Ns * Ns




89

Table 18. The effect of humic acid and nitrogen on leaf area index (LAI) of

maize genotypes at silking


Genotypes

3025 3.55 c 3.64 c 3.59 c

55w65 4.17 a 4.35 a 4.26 a

Jalal 3.82 b 3.95 b 3.88 b

Iqbal 3.24 d 3.42 d 3.33 d

LSD(0.05) 0.08 0.02 0.04

SE 0.03 0.01 0.02


0 3.59 d 3.73 d 3.66 d

0.6 3.66 c 3.80 c 3.73 c

1.2 3.72 b 3.87 b 3.80 b

1.8 3.80 a 3.96 a 3.88 a

LSD(0.05) 0.02 0.01 0.02

SE 0.01 0.01 0.01

Nitrogen (kg ha-1)

0 3.14 d 3.26 d 3.20 d

120 3.55 c 3.70 c 3.62 c

180 3.89 b 4.06 b 3.98 b

240 4.20 a 4.34 a 4.27 a

LSD(0.05) 0.01 0.02 0.01

SE 0.01 0.01 0.01



N×G * * * (Fig. 18b)

HA×G * * * (Fig. 18c)

HA×G×N Ns * * (Fig. 18d)




90

Figure 17a: Interaction between N×G for leaf area (cm2) plant-1 of maize at silking.


Figure 18a: Interaction between N×HA for LAI of maize at silking. Vertical bars


Figure 18b: Interaction between N×G for LAI of maize at silking. Vertical bars


3600

4400

5200

6000

6800

7600

0 120 180 240

Lea

f a

rea

pla

nt-1

(cm

2)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

2.8

3.3

3.8

4.3

4.8

0 0.6 1.2 1.8

Lea

f a

rea i

nd

ex (

LA

I)


N×HA

0

120

180

240

2.5

3.1

3.7

4.3

4.9

5.5

0 120 180 240

Lea

f a

rea

in

dex

(L

AI)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

91

Figure 18c: Interaction between HA×G for LAI of maize at silking. Vertical bars


Figure 18d: Interaction between G×HA×N for LAI of maize at silking. Vertical bars


2.5

3.0

3.5

4.0

4.5

5.0

5.5

0 0.6 1.2 1.8

Lea

f are

a i

nd

ex (

LA

I)


3025 (HA×N)

0

120

180

240 2.5

3.0

3.5

4.0

4.5

5.0

5.5

0 0.6 1.2 1.8

Lea

f are

a i

nd

ex (

LA

I)


55w65 (HA×N)

0

120

180

240

2.5

3.0

3.5

4.0

4.5

5.0

5.5

0 0.6 1.2 1.8

Lea

f a

rea

in

dex

(L

AI)


Jalal (HA×N)

0

120

180

2402.5

3.0

3.5

4.0

4.5

5.0

5.5

0 0.6 1.2 1.8

Lea

f a

rea

in

dex

(L

AI)


Iqbal (HA×N)

0

120

180

240

3.0

3.4

3.8

4.2

4.6

0 0.6 1.2 1.8

Lea

f a

rea

in

dex

(L

AI)


HA×G

3025

55w65

Jalal

Iqbal

92

4.3.5 Specific leaf area (SLA) plant-1 at silking

Data analysis indicated that genotypes, HA and N application rates considerably

affected specific leaf area (SLA) plant-1 of maize (Table 19). The N×G and HA×G

interactions were significant. The effect of years was also significant as a source of

variation. Highest specific leaf area (SLA) plant-1 (211.39 cm2 g-1) was observed in

plots sown with Iqbal variety, followed by OPV Jalal (185.03 cm2 g-1) while lower SLA

plant-1 was produced by 3025 (193.43 cm2 g-1). Moreover, HA application at the rate of

1.8 kg ha-1 produced lowest SLA plant-1 (185.42 cm2 g-1), followed by HA application

at the rate of 1.2 kg ha-1 (188.07 cm2 g-1) while no HA treated plots resulted in higher

SLA plant-1 (196.07 cm2 g-1). Similarly, SLA plant-1 was higher in control plots of N

(210.55 cm2 g-1), followed by 140 kg ha-1 N (196.89 cm2 g-1) while those units treated

with 240 kg ha-1 N provided lower SLA plant-1 (170.96 cm2 g-1).

The interaction of N×G suggested that SLA plant-1 at silking stage of maize genotypes

decreased in a linear fashion with the increase in N levels. Moreover, the observed trend

was higher for hybrid 55w65 against other maize genotypes (Fig. 19a). The interaction

of HA×G indicated the negative response of maize genotypes regarding SLA plant-1 to

humic acid applications at silking stage of crop growth. However, the response was

higher for 55w65 when compared with other maize genotypes (Fig. 19b).

4.3.6 Leaf area ratio (LAR) plant-1 at silking

Statistical perusal of the data revealed that genotypes, humic acid and N

fertilizer appreciably affected leaf area ratio (LAR) plant-1 of maize (Table 20). The

interactions of N×G and HA×G were found significant. Regarding genotypes, OPV

Jalal produced higher LAR (52.17 cm2 g-1) which was at par with Iqbal (50.78 cm2 g-1)

while 3025 and 55w65 resulted in lower LAR plant-1 (45.99 cm2 g-1 and 45.33 cm2 g-1

respectively). Likewise, humic acid application at the rate of 1.8 kg ha-1 produced

lowest LAR (48.01 cm2 g-1), followed by HA application at the rate of 1.2 kg ha-1 (48.34

cm2 g-1) while control plots of humic acid resulted in higher LAR (49.06 cm2 g-1).

Furthermore, N application at the rate of 240 kg ha-1 produced lower LAR (46.10 cm2

g-1), followed by 180 kg ha-1 N (46.57 cm2 g-1) while control plots of N (0 kg N ha-1)

produced higher LAR (52.74 cm2 g-1).

The interaction of N×G revealed that LAR plant-1 at silking stage of maize genotypes

showed a well response to the application of N fertilizer. However, maize hybrid 55w65

93

exhibited greater response in comparison to other maize genotypes (Fig. 20a). The

interaction HA×G indicated the significant response of maize genotypes to the

application of humic acid for LAR plant-1 at silking stage. Moreover, hybrid 55w65

showed more response among all maize genotypes in this regard (Fig. 20b).

Table 19. The effect of humic acid and nitrogen on specific leaf area (cm2 g-1)

plant-1 of maize genotypes at silking


Genotypes

3025 201.85 b 185.01 b 193.43 b

55w65 175.50 c 166.11 d 170.81 d

Jalal 192.81 b 177.24 c 185.03 c

Iqbal 217.79 a 204.99 a 211.39 a

LSD(0.05) 11.70 6.18 5.89

SE 4.78 2.52 2.70


0 203.17 a 188.96 a 196.07 a

0.6 198.11 b 184.11 b 191.11 b

1.2 195.07 c 181.07 c 188.07 c

1.8 191.61 d 179.22 d 185.42 d

LSD(0.05) 3.56 2.82 2.21

SE 1.72 1.37 1.10

Nitrogen (kg ha-1)

0 219.21 a 201.90 a 210.55 a

120 204.49 b 189.30 b 196.89 b

180 188.77 c 175.73 c 182.25 c

240 175.49 d 166.42 d 170.96 d

LSD(0.05) 1.46 1.29 0.97

SE 0.74 0.65 0.49


N×HA Ns * Ns

N×G * * * (Fig. 19a)

HA×G Ns Ns * (Fig. 19b)

HA×G×N Ns Ns Ns




94

Figure 19a: Interaction between N×G for SLA (cm2 g-1) plant-1 of maize at silking.


Figure 19b: Interaction between HA×G for SLA (cm2 g-1) plant-1 of maize at silking.

Vertical bars represent erroe of mean in each interaction.

140

160

180

200

220

240

260

0 120 180 240

Sp

ecif

ic lea

f a

rea

(S

LA

) p

lan

t-1a

t si

lkin

g

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

160

170

180

190

200

210

220

230

0 0.6 1.2 1.8

Sp

ecif

ic lea

f are

a (

SL

A)

pla

nt-1

at

silk

ing


HA×G

3025

55w65

Jalal

Iqbal

95

Table 20. The effect of humic acid and nitrogen on leaf area ratio (cm2 g-1)

plant-1 of maize genotypes at silking


Genotypes

3025 46.05 b 45.92 b 45.99 b

55w65 45.71 b 44.96 b 45.33 b

Jalal 52.17 a 52.17 a 52.17 a

Iqbal 51.45 a 50.12 a 50.78 a

LSD(0.05) 1.99 2.91 1.57

SE 0.81 1.19 0.72


0 49.29 a 48.82 a 49.06 a

0.6 49.09 a 48.64 a 48.86 a

1.2 48.57 a 48.11 b 48.34 b

1.8 48.43 a 47.60 b 48.01 b

LSD(0.05) 0.69 0.79 0.51

SE 0.33 0.38 0.25

Nitrogen (kg ha-1)

0 53.34 a 52.13 a 52.74 a

120 49.30 b 48.43 b 48.87 b

180 46.82 c 46.33 c 46.57 c

240 45.92 d 46.28 c 46.10 d

LSD(0.05) 0.34 0.26 0.21

SE 0.17 0.13 0.11



N×G * * * (Fig. 20b)

HA×G Ns * Ns

HA×G×N Ns * Ns




96

Figure 20a: Interaction between N×HA for LAR (cm2 g-1) plant-1 of maize at silking.


Figure 20b: Interaction between HA×G for LAR (cm2 g-1) plant-1 of maize at silking.


44

46

48

50

52

54

0 0.6 1.2 1.8

Lea

f a

rea

ra

tio

(L

AR

) p

lan

t-1a

t si

lkin

g


N×HA

0

120

180

240

43

45

47

49

51

53

55

0 0.6 1.2 1.8

Lea

f are

a r

ati

o (

LA

R)

at

silk

ing


HA×G

3025

55w65

Jalal

Iqbal

97



4.4.1 Productive plants m-2

Statistical perusal of the data exhibited that genotypes, humic acid, nitrogen and

years considerably affected the number of maize productive plants m-2 (Table 21). The

N×HA and N×G interactions were found to be significant. More productive plants m-2

were recorded for hybrid 3025 and 55w65 (6.56 and 6.48 respectively) while Iqbal and

Jalal varieties produced lower number of productive plants m-2 (6.21 and 6.19

respectively). Similarly, more productive plants m-2 were observed in plots received HA

at the rate of 1.8 kg ha-1 (6.47), followed by HA application of 1.2 kg ha-1 (6.39) while

control plots of HA (0 kg HA ha-1) produced less number of plants m-2 (6.25). Likewise,

nitrogen also increased the number of productive plants m-2 as its dose increased from

0 to 240 kg ha-1. The number of productive plants m-2 was higher in plots treated with

240 kg ha-1 N (6.86), followed by 180 kg ha-1 N (6.64) while plots with 0 kg N ha-1

(control) produced lower number of maize productive plants m-2 (5.73).

The interaction of N×HA revealed that N levels responded linearly to the

applications of humic acid regarding productive plants m-2 of maize genotypes. The

plots treated with 120 and 180 kg ha-1 N exhibited higher response as compared to other

N levels against humic acid applications, however, more productive plants m-2 were

recorded at 240 N ha-1 (Fig. 21a). The interaction N×G indicated the significant

relationship among these factors for number of productive plants m-2. The plots sown

with OPVs Jalal and Iqbal showed higher response against N application levels,

however, hybrid 3025 provided more productive plants m-2 as compared to other maize

genotypes. (Fig. 21b). The interaction HA×G suggested the well response of maize

genotypes to humic acid applications regarding productive plants m-2. Moreover, the

hybrid 3025 exhibited more substantial response as compared to other maize genotypes

(Fig. 21c). The interaction G×HA×N revealed the significant differences among maize

genotypes regarding productive plants m-2 due to N and humic acid application.

Productive plants m-2 increased with increase in N and HA for all genotypes. The

application of N at 180 kg ha-1 with increasing humic acid considerably enhanced

productive plants m-2 in maize genotypes. However the same response was higher in

OPV Jalal at 120 kg N ha-1 (Fig. 21d).

98

Table 21. The effect of humic acid and nitrogen on productive plants m-2 of

maize genotypes


Genotypes

3025 6.44 a 6.67 a 6.56 a

55w65 6.35 a 6.61 b 6.48 b

Jalal 5.88 b 6.51 c 6.19 c

Iqbal 6.02 b 6.41 d 6.21 c

LSD(0.05) 0.16 0.04 0.07

SE 0.06 0.02 0.03


0 6.06 d 6.44 d 6.25 d

0.6 6.13 c 6.52 c 6.32 c

1.2 6.21 b 6.58 b 6.39 b

1.8 6.29 a 6.65 a 6.47 a

LSD(0.05) 0.06 0.04 0.03

SE 0.03 0.02 0.02

Nitrogen (kg ha-1)

0 5.49 d 5.97 d 5.73 d

120 6.01 c 6.42 c 6.22 c

180 6.46 b 6.81 b 6.64 b

240 6.74 a 6.98 a 6.86 a

LSD(0.05) 0.02 0.01 0.01

SE 0.01 0.01 0.01


N×HA * * * (Fig. 21a)

N×G * * * (Fig. 21b)

HA×G * * * (Fig. 21c)

HA×G×N * Ns * (Fig. 21d)




99

Figure 21a: Interaction between N×HA for productive plants m-2 of maize. Vertical


Figure 21b: Interaction between N×G for productive plants m-2 of maize. Vertical


Figure 21c: Interaction between HA×G for productive plants m-2 of maize. Vertical


5.4

5.7

6.0

6.3

6.6

6.9

7.2

0 0.6 1.2 1.8

Pro

du

ctiv

e p

lan

ts m

-2


N×HA

0

120

180

240

5.0

5.5

6.0

6.5

7.0

7.5

0 120 180 240

Pro

du

ctiv

e p

lan

ts m

-2

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

5.9

6.1

6.3

6.5

6.7

6.9

0 0.6 1.2 1.8

Pro

du

ctiv

e p

lan

ts m

-2


HA×G

3025

55w65

Jalal

Iqbal

100

Figure 21d: Interaction between G×HA×N for productive plants m-2 of maize.


5.0

5.5

6.0

6.5

7.0

7.5

0 0.6 1.2 1.8

Pro

du

ctiv

e p

lan

ts m

-2


3025 (HA×N)

0

120

180

240

5.0

5.5

6.0

6.5

7.0

7.5

0 0.6 1.2 1.8

Pro

du

ctiv

e p

lan

ts m

-2


55w65 (HA×N)

0

120

180

240

5.0

5.5

6.0

6.5

7.0

7.5

0 0.6 1.2 1.8Pro

du

ctiv

e p

lan

ts m

-2


Jalal (HA×N)

0

120

180

240

5.0

5.5

6.0

6.5

7.0

7.5

0 0.6 1.2 1.8

Pro

du

ctiv

e p

lan

ts m

-2


Iqbal (HA×N)

0

120

180

240

101

4.4.2 Ears plant-1

Statistical analysis of the data indicated that genotypes, N fertilizer and humic

acid substantially affected ears plant-1 of maize (Table 22). The interactions of N×HA

and N×G were found significant. The effect of years was also significant as a source of

variation. More ears plant-1 were recorded in 55w65 (0.95), followed by hybrid 3025

(0.94) while the lower number of ears plant-1 was observed in OPVs Jalal (0.88).

Likewise, higher ears plant-1 were reported in the experimental units treated with HA

at the rate of 1.8 kg ha-1 (0.93), followed by 1.2 kg HA ha-1 (0.92) while less ears plant-

1 were observed in control plots having no humic acid application (0.90). Regarding

nitrogen levels, the ear bearing potential of maize genotypes increased as the rate of

nitrogen enhanced from 0 to 240 kg ha-1. Higher ears plant-1 (1.00) were recorded in

those plots received 240 kg ha-1 N, followed by 180 kg ha-1 N (0.96) while control plots

(0 kg N ha-1) produced lower number of ears plant-1 (0.81).

The interaction N×HA suggested that N levels responded in a linear way to the

amount of humic acid applied regarding the number of ears plant-1 in maize genotypes.

However, the plots supplied with 120 kg ha-1 N showed higher response to humic acid

application in comparison to other N levels (Fig. 22a). The interaction N×G exhibited

that the ear bearing capacity of maize genotypes increased significantly with the

successive applications of N fertilizer. The plots sown with OPVs Jalal and Iqbal

indicated a substantial increase in ears plant-1 in comparison to other maize genotypes,

although more ears plant-1 were observed in 55w65 and 3025. (Fig. 22b). The

interaction of HA×G revealed that the number of ears plant-1 increased with the increase

of humic acid. However, the hybrid 55w65 exhibited more response in comparison to

other maize genotypes (Fig. 22c).

4.4.3 Ears m-2

Statistical perusal of the data revealed that genotypes, HA and N levels

significantly affected the number of ears m-2 (Table 23). The interactions N×HA, N×G

and HA×G were found to be significant. Higher number of ears m-2 were observed in

hybrid 3025 and 55w65 (6.60 and 6.53 respectively), followed by OPV Iqbal (6.22)

which was at par with Jalal (6.18). Similarly, number of ears m-2 was higher in the sub-

subplots treated with 1.8 kg ha-1 humic acid (6.52), followed by 1.2 kg ha-1 HA (6.42)

while lower number of ears m-2 were recorded in control plots of humic acid (6.26).

102

Likewise, N application at the rate of 240 kg ha-1 produced more ears m-2 (6.93),

followed by 180 kg ha-1 N (6.69) while control plots of N provided lower number of

ears m-2 (5.70).

The interaction N×HA demonstrated the well response of N to the applied levels

of humic acid in maize genotypes in terms of ears m-2. Moreover, the plots

supplemented with 120 and 180 kg ha-1 N showed a marked increase in terms of ears

m-2 when compared with other levels of N against humic acid application (Fig. 23a). In

addition, the interaction N×G exhibited the linear response of maize genotypes

regarding number of ears m-2 to the increase in levels of N fertilizer. However, the plots

treated with OPVs Iqbal and Jalal showed more response for increase in ears m-2 as

compared to other maize genotypes (Fig. 23b). Likewise, the interaction HA×G

revealed the linear relationship among HA applications and maize genotypes regarding

ears m-2. The hybrid 3025 and OPV Iqbal showed more response to humic acid

application in comparison to other maize genotypes (Fig. 23c).

103

Table 22. The effect of humic acid and nitrogen on ears plant-1 of maize

genotypes


Genotypes

3025 0.92 a 0.96 b 0.94 b

55w65 0.94 a 0.97 a 0.95 a

Jalal 0.84 c 0.93 c 0.88 c

Iqbal 0.87 b 0.91 d 0.89 d

LSD(0.05) 0.03 0.01 0.01

SE 0.01 0.01 0.01


0 0.87 d 0.92 c 0.90 d

0.6 0.89 c 0.93 b 0.91 c

1.2 0.90 b 0.95 a 0.92 b

1.8 0.91 a 0.95 a 0.93 a

LSD(0.05) 0.01 0.01 0.01

SE 0.01 0.01 0.01

Nitrogen (kg ha-1)

0 0.78 d 0.84 d 0.81 d

120 0.87 c 0.92 c 0.90 c

180 0.94 b 0.98 b 0.96 b

240 0.98 a 1.01 a 1.00 a

LSD(0.05) 0.01 0.02 0.01

SE 0.01 0.01 0.01


N×HA * * * (Fig. 22a)

N×G * * * (Fig. 22b)


HA×G×N Ns Ns Ns




104

Figure 22a: Interaction between N×HA for ears plant-1 of maize. Vertical bars


Figure 22b: Interaction between N×G for ears plant-1 of maize. Vertical bars


Figure 22c: Interaction between HA×G for ears plant-1 of maize. Vertical bars


0.75

0.83

0.91

0.99

1.07

0 0.6 1.2 1.8

Ea

rs p

lan

t-1


N×HA

0

120

180

240

0.70

0.80

0.90

1.00

1.10

0 120 180 240

Ea

rs p

lan

t-1

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

0.83

0.88

0.93

0.98

1.03

0 0.6 1.2 1.8

Ea

rs p

lan

t-1


HA×G

3025

55w65

Jalal

Iqbal

105

Table 23. The effect of humic acid and nitrogen on ears m-2 of maize genotypes


Genotypes

3025 6.49 a 6.72 a 6.60 a

55w65 6.38 a 6.69 a 6.53 a

Jalal 5.87 b 6.49 b 6.18 b

Iqbal 6.03 b 6.42 c 6.22 b

LSD(0.05) 0.19 0.04 0.09

SE 0.08 0.02 0.04


0 6.07 d 6.44 d 6.24 d

0.6 6.15 c 6.54 c 6.35 c

1.2 6.23 b 6.61 b 6.43 b

1.8 6.32 a 6.72 a 6.53 a

LSD(0.05) 0.05 0.04 0.03

SE 0.02 0.02 0.02

Nitrogen (kg ha-1)

0 5.52 d 6.00 d 5.70 d

120 6.02 c 6.43 c 6.22 c

180 6.46 b 6.81 b 6.69 b

240 6.78 a 7.09 a 6.93 a

LSD(0.05) 0.02 0.02 0.01

SE 0.01 0.01 0.01



N×G * * * (Fig. 23b)


HA×G×N Ns Ns Ns




106

Figure 23a: Interaction between N×HA for ears m-2 of maize. Vertical bars represent

standard error of mean in each interaction.

Figure 23b: Interaction between N×G for ears m-2 of maize. Vertical bars represent


Figure 23c: Interaction between HA×G for ears m-2 of maize. Vertical bars represent


5.3

5.7

6.1

6.5

6.9

7.3

0 0.6 1.2 1.8

Ea

rs m

-2


NxHA

0

120

180

240

5.0

5.5

6.0

6.5

7.0

7.5

0 120 180 240

Ea

rs m

-2

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

5.8

6.0

6.2

6.4

6.6

6.8

7.0

0 0.6 1.2 1.8

Ears

m-2


HA×G

3025

55w65

Jalal

Iqbal

107

4.4.4 Ear weight plant-1 at maturity

Statistical analysis of the data indicated that genotypes, humic acid, nitrogen

and years markedly influenced ear weight of maize at maturity (Table 24). The

interactions N×HA, N×G, HA×G and N×HA×G were significant. More ear weight

plant-1 of maize was recorded in hybrid 55w65 (138.83 g), followed by 3025 (128.40

g) while Iqbal variety resulted in lower ear weight plant-1 (94.73 g). Likewise, higher

ear weight plant-1 was found in the plots supplemented with 1.8 kg ha-1 humic acid

(122.50 g), followed by 1.2 kg HA ha-1 (117.92 g) while lower ear weight plant-1 was

noted in control plots of humic acid (109.20 g). As expected, N application increased

ear weight plant-1 of maize as its application increased from 0 to 240 kg N ha-1.

Application of N at the rate of 240 kg ha-1 produced more ear weight plant-1 (144.25 g),

followed by 180 kg N ha-1 (128.43 g) while control plots of N (0 kg N ha-1) produced

lower ear weight plant-1 of maize (83.34 g).

The interaction of N×HA indicated the linear response of N levels regarding ear

weight plant-1 of maize genotypes to the humic acid applications. However, the

treatment of 120 kg ha-1 N showed higher response when compared with other N levels

(Fig. 24a). The interaction of N×G evaluated the significant response of maize

genotypes to N levels regarding ear weight plant-1 at maturity. Moreover, the highest

response was recorded for hybrid 55w65 agains other genotypes (Fig. 24b). The

interaction HA×G showed the linear relationship among maize genotypes and humic

acid applications regarding ear weight plant-1 at physiological maturity. The hybrid

55w65 exhibited much better response in this regard (Fig. 24c). The interaction

G×HA×N revealed that ear weight plant-1 of maize genotypes responded in a well

manner to the humic acid and N applications. However, the application of N at 120 kg

ha-1 with increasing HA notably increased ear weight of hybrid 55w65 as compared to

other maize genotypes (Fig. 24d).

108

Table 24. The effect of humic acid and nitrogen on ear weight (g) plant-1 of



Genotypes

3025 127.15 b 129.65 b 128.40 b

55w65 137.38 a 140.27 a 138.83 a

Jalal 99.10 c 102.97 c 101.03 c

Iqbal 93.72 d 96.75 d 94.73 d

LSD(0.05) 2.31 2.19 1.42

SE 0.94 0.90 0.65


0 107.96 d 110.44 d 109.20 d

0.6 112.04 c 114.69 c 113.36 c

1.2 116.32 b 119.52 b 117.92 b

1.8 120.02 a 124.99 a 123.67 a

LSD(0.05) 0.76 1.19 0.69

SE 0.37 0.58 0.34

Nitrogen (kg ha-1)

0 1.71 d 84.96 d 83.34 d

120 106.30 c 107.66 c 106.98 c

180 126.84 b 130.02 b 128.43 b

240 141.50 a 146.99 a 144.25 a

LSD(0.05) 0.41 0.80 0.45

SE 0.20 0.40 0.23



N×G * * * (Fig. 24b)

HA×G * * * (Fig. 24c)

HA×G×N * Ns * (Fig. 24d)




109

Figure 24a: Interaction between N×HA for ear weight (g) plant-1 of maize at


interaction.

Figure 24b: Interaction between N×G for ear weight (g) plant-1 of maize at maturity.


Figure 24c: Interaction between HA×G for ear weight (g) plant-1 of maize at


interaction.

67

87

107

127

147

167

0 0.6 1.2 1.8Ea

r w

igh

t (g

) p

lan

t-1a

t

ma

turi

ty


N×HA

0

120

180

240

55

85

115

145

175

205

0 120 180 240Ear

wei

gh

t (g

) p

lan

t-1at

matu

rity

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

80

100

120

140

160

0 0.6 1.2 1.8Ea

r w

eig

ht

(g)

pla

nt-1

at

ma

turi

ty


HA×G

3025

55w65

Jalal

Iqbal

110

Figure 24d: Interaction between G×HA×N for ear weight (g) plant-1 of maize at


interaction.

60

90

120

150

180

210

0 0.6 1.2 1.8

Ea

r w

eig

ht

(g)

pla

nt-1

at

ma

turi

ty


3025 (HA×N)

0

120

180

240

60

90

120

150

180

210

0 0.6 1.2 1.8

Ear

wei

gh

t (g

) p

lan

t-1a

t

ma

turi

ty


55w65 (HA×N)

0

120

180

240

60

90

120

150

180

210

0 0.6 1.2 1.8

Ear

wei

gh

t (g

) p

lan

t-1at

matu

rity


Jalal (HA×N)

0

120

180

240

60

90

120

150

180

210

0 0.6 1.2 1.8

Ea

r w

eig

ht

(g)

pla

nt-1

at

ma

turi

ty


Iqbal (HA×N)

0

120

180

240

111

4.4.5 Ear length (cm)

Statistical perusal of the data showed that genotypes, humic acid and nitrogen

significantly affected ear length of maize (Table 25). The N×HA, G×N and HA×G

interactions were found to be significant. As a source of variation the impact of years

was also found to be significant. Ear length was higher in samples of 55w65 (20.05

cm), followed by 3025 (18.36 cm) while Jalal and Iqbal cultivars resulted in lower ear

length of maize (17.82 cm and 16.62 cm respectively). Similarly, humic acid

application at the rate of 1.8 kg ha-1 resulted in higher ear length (18.58 cm), followed

by 1.2 kg HA ha-1 (18.34 cm) while control plots of humic acid (0 kg HA ha-1) produced

lower ear length (17.86 cm). Likewise, 240 kg ha-1 N application produced higher ear

length (20.12 cm), followed by 180 kg ha-1 N (19.06 cm) while control treatments of N

(0 kg N ha-1) provided lower ear length (15.76 cm).

The interaction of N×HA revealed the well response of N levels to the

successive applications of humic acid regarding ear length in maize genotypes.

However, the plots supplied with 240 kg ha-1 N produced lengthy ears as compared to

other N levels in response to humic acid application (Fig. 25a). Likewise, the interaction

of N×G indicated the linear relationship among maize genotypes and N levels in terms

of ear length. Moreover, the plots of 55w65 produced lengthy ears in comparison to

other maize genotypes (Fig. 25b). The interaction HA×G indicated the substantial

impact of humic acid on ear length of maize genotypes. However, the plots treated with

hybrid 55w65 provided greater ear length in comparison to other maize genotypes (Fig.

25c).

4.4.6 Ear girth (cm)

Data analysis revealed that genotypes, humic acid, nitrogen and years

significantly affected ear girth of maize (Table 26). The N×HA, N×G and N×HA×G

interactions were found to be significant. Regarding genotypes, higher ear girth was

reported in samples of 55w65 (15.00 cm), followed by 3025 (13.92 cm) while Iqbal

variety resulted in lower ear girth of maize (12.85 cm). In addition, humic acid

application at the rate of 1.8 kg ha-1 resulted in higher ear girth (14.16 cm), followed by

HA level of 1.2 kg ha-1 (13.96 cm) while lower ear girth was observed in control humic

acid (0 kg HA ha-1) plots (13.50 cm). Likewise, N fertilizer applied at the rate of 240

kg ha-1 produced higher ear girth (15.36 cm), followed by 180 kg ha-1 N (14.68 cm)

112

while those plots in which no N was applied (0 kg N ha-1) resulted in least ear girth

(11.58 cm).

The interaction of N×HA suggested that N fertilizer had a well response to the

increase in humic acid levels regarding ear girth of maize genotypes. The plots treated

with 180 and 240 kg ha-1 N significantly produced plants of higher ear girth in

comparison to other N levels (Fig. 26a). The interaction N×G showed the significant

impact of N fertilization on ear girth of maize genotypes. The sub-subplots sown with

55w65 and Jalal exhibited more response when compared with other genotypes (Fig.

26b). ). The interaction HA×G indicated the notable influence of humic acid on ear

girth of maize genotypes. However, 55w65 exhibited more response in comparison to

other genotypes (Fig. 26c). The interaction G×HA×N indicated that ear girth of maize

genotypes improved linearly with the application of humic acid and N fertilization.

However, 55w65 showed a considerable increase in ear girth as compared to 3025. The

same trend was also reported for OPV Jalal against Iqbal (Fig. 26d).

113

Table 25. The effect of humic acid and nitrogen on ear length (cm) of maize

genotypes


Genotypes

3025 18.35 b 18.37 b 18.36 b

55w65 20.03 a 20.08 a 20.05 a

Jalal 17.77 c 17.90 c 17.84 c

Iqbal 16.55 d 16.69 d 16.62 d

LSD(0.05) 0.19 0.16 0.11

SE 0.08 0.06 0.05


0 17.81 d 17.90 d 17.86 d

0.6 18.04 c 18.14 c 18.09 c

1.2 18.28 b 18.40 b 18.34 b

1.8 18.55 a 18.60 a 18.58 a

LSD(0.05) 0.06 0.09 0.05

SE 0.03 0.04 0.03

Nitrogen (kg ha-1)

0 15.74 d 15.78 d 15.76 d

120 17.87 c 18.00 c 17.94 c

180 19.00 b 19.11 b 19.06 b

240 20.08 a 20.15 a 20.12 a

LSD(0.05) 0.05 0.04 0.03

SE 0.02 0.02 0.02



N×G * * * (Fig. 25b)


HA×G×N Ns Ns Ns




114

Table 26. The effect of humic acid and nitrogen on ear girth (cm) of maize

genotypes


Genotypes

3025 13.86 b 13.99 b 13.92 b

55w65 14.94 a 15.07 a 15.00 a

Jalal 13.44 c 13.67 c 13.55 c

Iqbal 12.74 d 12.96 d 12.85 d

LSD(0.05) 0.06 0.06 0.04

SE 0.02 0.03 0.02


0 13.47 d 13.53 d 13.50 d

0.6 13.63 c 13.79 c 13.71 c

1.2 13.84 b 14.08 b 13.96 b

1.8 14.03 a 14.29 a 14.16 a

LSD(0.05) 0.03 0.09 0.05

SE 0.02 0.04 0.02

Nitrogen (kg ha-1)

0 11.53 d 11.64 d 11.58 d

120 13.58 c 13.82 c 13.70 c

180 14.56 b 14.80 b 14.68 b

240 15.30 a 15.43 a 15.36 a

LSD(0.05) 0.02 0.06 0.03

SE 0.01 0.03 0.02



N×G * * * (Fig. 26b)


HA×G×N * * * (Fig. 26d)




115

Figure 25a: Interaction between N×HA for ear length (cm) of maize. Vertical bars


Figure 25b: Interaction between N×G for ear length (cm) of maize. Vertical bars


Figure 25c: Interaction between HA×G for ear length (cm) of maize. Vertical bars


14.2

15.8

17.4

19.0

20.6

22.2

0 0.6 1.2 1.8

Ea

r le

ng

th (

cm)


N×HA

0

120

180

240

13.4

15.7

18.0

20.3

22.6

24.9

0 120 180 240

Ear

len

gth

(cm

)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

15.3

16.5

17.7

18.9

20.1

21.3

0 0.6 1.2 1.8

Ea

r le

ng

th (

cm)


HA×G

3025

55w65

Jalal

Iqbal

116

Figure 26a: Interaction between N×HA for ear girth (cm) of maize. Vertical bars


Figure 26b: Interaction between N×G for ear girth (cm) of maize. Vertical bars


Figure 26c: Interaction between HA×G for ear girth (cm) of maize. Vertical bars


10.2

11.4

12.6

13.8

15.0

16.2

0 0.6 1.2 1.8

Ea

r g

irth

(cm

)


N×HA

0

120

180

240

9.2

11.0

12.8

14.6

16.4

18.2

0 120 180 240

Ear

gir

th (

cm)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

11.6

12.5

13.4

14.3

15.2

16.1

0 0.6 1.2 1.8

Ea

r g

irth

(cm

)


HA×G

3025

55w65

Jalal

Iqbal

117

Figure 26d: Interaction between G×HA×N for ear girth (cm) of maize. Vertical bars


9.0

11.0

13.0

15.0

17.0

0 0.6 1.2 1.8

Ea

r g

irth

(cm

)


3025 (HA×N)

0

120

180

240

9.0

11.0

13.0

15.0

17.0

0 0.6 1.2 1.8

Ear

gir

th (

cm)


55w65 (HA×N)

0

120

180

240

9.0

11.0

13.0

15.0

17.0

0 0.6 1.2 1.8

Ear

gir

th (

cm)


Jalal (HA×N)

0

120

180

240

9.0

11.0

13.0

15.0

17.0

0 0.6 1.2 1.8

Ea

r g

irth

(cm

)


Iqbal (HA×N)

0

120

180

240

118

4.4.7 Rows ear-1

Statistical perusal of the data showed that genotypes, humic acid, nitrogen and

years significantly affected the number of grain rows ear-1 in maize (Table 27). The

N×HA and N×G interactions were found significant. Regarding genotypes, more

number of rows ear-1 were observed in 55w65 (13.15), followed by 3025 (12.60) which

was at par with Jalal variety (12.48) while Iqbal variety resulted in lower number of

rows ear-1 (12.01). Similarly, humic acid application linearly enhanced rows ear-1 of

maize. More rows ear-1 were counted in plots treated with 1.8 kg ha-1 HA (12.83),

followed by 1.2 kg ha-1 HA (12.69) while plots without HA resulted in plants having

less rows ear-1 (12.27). Moreover, rows ear-1 increased as N application rate accelerated

from 0 to 240 kg ha-1. Higher rows ear-1 were collected from those sub-subplots received

240 kg ha-1 N (13.91), followed by 180 kg ha-1 N (13.25) while lower rows ear-1 were

collected from control plots of N (10.89).

The interaction N×HA evaluated the significant response of N fertilizer to the

humic acid applications in maize genotypes with respect to grain rows ear-1. However,

240 kg ha-1 N exhibited much higher response to humic acid application in comparison

to other N levels regarding rows ear-1 (Fig. 27a). The interaction N×G showed the linear

relationship among maize genotypes and nitrogen levels regarding grain rows ear-1.

Furthermore, the plots of 55w65 exhibited a substantial increase in rows ear-1 while

comparing with other maize genotypes (Fig. 27b).

4.4.8 Grains row-1

Data analysis revealed that genotypes, HA, N and years considerably influenced

grains row-1 of maize (Table 28). The interactions of N×HA and N×G were found to be

significant. Higher number of grains row-1 were counted in 55w65 (35.19) which was

at par with hybrid 3025 (34.15) while OPV Iqbal resulted in lower number of grains

row-1 (31.47). Similarly, HA application linearly increased number of grains row-1 of

maize. More number of grains row-1 were reported in plots treated with 1.8 kg ha-1 HA

(34.20), followed by 1.2 kg ha-1 HA application (33.79) while plots without HA resulted

in less number of grains row-1 (32.03). Moreover, total of grains row-1 enhanced as N

application rate increased from 0 to 240 kg ha-1. Higher grains row-1 were observed in

plots supplemented with 240 kg ha-1 N (36.33), followed by 180 kg ha-1 N (34.93) while

lower grains row-1 were observed in samples collected from control plots of N (29.92).

119

The interaction of N×HA exhibited the well response of N in maize genotypes

to the applied levels of humic acid regarding grains row-1. The units treated with 120

and 180 kg ha-1 N showed higher response to humic acid application in comparison to

other levels of N fertilizer. However, more grains row-1 were recorded at 240 kg N ha-

1 (Fig. 28a). The interaction N×G revealed the responsive natures of maize genotypes

to N applications as far as grains row-1 are concerned. Moreover, the plots sown with

55w65 and 3025 proved superior in this regard to other maize genotypes (Fig. 28b).

Likewise, the interaction HA×G showed the significant response of maize genotypes to

the increase in humic acid levels. However, 55w65 and 3025 recorded higher response

as compared to other maize genotypes (Fig. 28c).

120

Table 27. The effect of humic acid and nitrogen on rows ear-1 of maize

genotypes


Genotypes

3025 12.48 b 12.73 b 12.60 b

55w65 12.98 a 13.32 a 13.15 a

Jalal 12.34 b 12.63 b 12.48 b

Iqbal 11.83 c 12.19 c 12.01 c

LSD(0.05) 0.17 0.31 0.16

SE 0.07 0.13 0.07


0 12.12 d 12.41 d 12.27 d

0.6 12.32 c 12.62 c 12.47 c

1.2 12.54 b 12.84 b 12.69 b

1.8 12.66 a 12.99 a 12.83 a

LSD(0.05) 0.08 0.08 0.05

SE 0.04 0.04 0.03

Nitrogen (kg ha-1)

0 10.74 d 11.05 d 10.89 d

120 12.07 c 12.31 c 12.19 c

180 13.08 b 13.41 b 13.25 b

240 13.74 a 14.08 a 13.91 a

LSD(0.05) 0.06 0.03 0.03

SE 0.03 0.02 0.02


N×HA * * * (Fig. 27a)

N×G * * * (Fig. 27b)

HA×G Ns Ns Ns

HA×G×N Ns Ns Ns




121

Table 28. The effect of humic acid and nitrogen on grains row-1 of maize

genotypes


Genotypes

3025 34.02 b 34.29 b 34.15 b

55w65 34.82 a 35.57 a 35.19 a

Jalal 33.42 b 33.70 b 33.56 c

Iqbal 31.15 c 31.79 c 31.47 d

LSD(0.05) 0.74 0.70 0.45

SE 0.30 0.29 0.21


0 32.79 d 33.26 d 33.03 d

0.6 33.10 c 33.61 c 33.36 c

1.2 33.56 b 34.03 b 33.79 b

1.8 33.96 a 34.44 a 34.20 a

LSD(0.05) 0.25 0.22 0.16

SE 0.12 0.11 0.08

Nitrogen (kg ha-1)

0 29.76 d 30.08 d 29.92 d

120 32.95 c 33.44 c 33.20 c

180 34.63 b 35.22 b 34.93 b

240 36.06 a 36.60 a 36.33 a

LSD(0.05) 0.06 0.05 0.04

SE 0.03 0.03 0.02


N×HA * * * (Fig. 28a)

N×G * * * (Fig. 28b)

HA×G * * * (Fig. 28c)

HA×G×N Ns Ns Ns




122

Figure 27a: Interaction between N×HA for grain rows ear-1 of maize. Vertical bars


Figure 27b: Interaction between N×G for grain rows ear-1 of maize. Vertical bars


10.0

11.0

12.0

13.0

14.0

15.0

0 0.6 1.2 1.8

Ro

ws

ear

-1


N×HA

0

120

180

240

9.5

10.6

11.7

12.8

13.9

15.0

16.1

0 120 180 240

Row

s ea

r-1


N×G

3025

55w65

Jalal

Iqbal

123

Figure 28a: Interaction between N×HA for grains row-1 of maize. Vertical bars


Figure 28b: Interaction between N×G for grains row-1 of maize. Vertical bars


Figure 28c: Interaction between HA×G for grains row-1 of maize. Vertical bars


28

30

32

34

36

38

0 0.6 1.2 1.8

Gra

ins

row

-1


N×HA

0

120

180

240

26

29

32

35

38

41

0 120 180 240

Gra

ins

row

-1

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

30

32

34

36

38

0 0.6 1.2 1.8

Gra

ins

row

-1


HA×G

3025

55w65

Jalal

Iqbal

124

4.4.9 Grains ear-1

Statistical data analysis indicated that genotypes, humic acid and N application

rate significantly affected maize grains ear-1 (Table 29). All of the interactions were

found to be significant. The impact of years was also significant as a source of variation.

Regarding genotypes, more number of grains ear-1 were counted in genotype 55w65

(465.26), followed by 3025 (439.57) while Iqbal variety resulted in less grains ear-1

(385.12). Likewise, the application of humic acid at the rate of 1.8 kg ha-1 resulted in

higher grains ear-1 (445.22), followed by HA application of 1.2 kg ha-1 (433.78) while

lower grains ear-1 were calculated in plots where no HA was applied (410.41).

Similarly, N application at the rate of 240 kg ha-1 provided higher grains ear-1 (508.12),

followed by N application level of 180 kg ha-1 (464.26) and 120 kg ha-1 (406.05) while

fewer grains ear-1 were reported in control plots of N fertilizer (332.89).

The interaction of N×HA exhibited the linear response of N fertilizer in maize

genotypes to the applications of humic acid regarding grains ear-1. However, the plots

supplied with 120 and 180 kg ha-1 N showed higher response in comparison to other N

levels, although more grains ear-1 were observed at 240 kg N ha-1 (Fig. 29a). The

interaction N×G revealed the substantial impact of N levels on grains ear-1 of maize

genotypes. Moreover, the plots treated with 55w65 produced higher grains ear-1 as

compared to other maize genotypes (Fig. 29b). The interaction HA×G indicated the

significant influence of humic acid on grains ear-1 of maize genotypes. The plots sown

with hybrid 55w65 provided higher grains ear-1 in comparison to other maize genotypes

(Fig. 29c). The interaction G×HA×N suggested that grains ear-1 of maize genotypes

improved in a linear way with the addition of humic acid and N levels. However, the

hybrid 55w65 markedly produced higher grains ear-1 and responded well to the humic

acid as well as N levels against other maize genotypes (Fig. 29d).

4.4.10 1000 grain weight (g)


years considerably affected 1000 grain weight of maize (Table 30). All of the

interactions were observed to be significant. Regarding genotypes, higher thousand

grain weight was produced by 55w65 (273.97 g), followed by hybrid 3025 (255.32 g)

while Jalal variety resulted in lower thousand grain weight (200.59 g). Similarly, HA

application linearly increased thousand grain weight of maize genotypes. Higher grain

125

weight was recorded in plots treated with 1.8 kg ha-1 HA (238.81 g), followed by 1.2

kg ha-1 HA application (236.25 g) while plots without HA resulted in lower thousand

grain weight (231.50 g). Moreover, thousand grain weight increased in a linear fashion

as N application rate enhanced from 0 level to 240 kg ha-1. Heavier grains were obtained

from plots supplied with 240 kg ha-1 N (251.22 g), followed by 180 kg ha-1 N (241.01

g) while lower thousand grain weight was recorded in samples collected from control

plots of N (218.08 g).

The N×HA interaction suggested that N fertilizer had a well response to the

application of humic acid as far as 1000 grain weight of maize genotypes is concerned.

However, 240 kg N ha-1 showed a marked increase in 1000 grain weight in comparison

to other N levels as a consequence of HA application (Fig. 30a). The interaction of N×G

exhibited that 1000 grain weight of maize genotypes responded in a significant manner

to the different application levels of N fertilizer. Hybrid 55w65 produced heavier grains

as compared to other maize genotypes (Fig. 30b). The interaction of HA×G indicated

the significant influence of humic acid on 1000 grain weight of maize genotypes.

Moreover, the plots sown with hybrid 3025 produced higher response in comparison to

other maize genotypes (Fig. 30c). The interaction G×HA×N showed that 1000 grain

weight of maize genotypes accelerated in a linear fashion with the application of humic

acid and N fertilizer. The hybrid 55w65 proved to be more responsive to the

applications of humic acid and nitrogen than other maize genotypes regarding 1000

grain weight. Higher response was recorded at 240 kg N ha-1 under 1.8 kg ha-1 humic

acid application (Fig. 30d).

126

Table 29. The effect of humic acid and nitrogen on grains ear-1 of maize

genotypes


Genotypes

3025 435.94 b 443.19 b 439.57 b

55w65 462.25 a 468.28 a 465.26 a

Jalal 416.74 c 426.02 c 421.38 c

Iqbal 379.96 d 390.27 d 385.12 d

LSD(0.05) 5.63 4.72 3.27

SE 2.30 1.93 1.50


0 407.00 d 413.83 d 410.41 d

0.6 418.37 c 425.47 c 421.92 c

1.2 429.45 b 438.11 b 433.78 b

1.8 440.08 a 450.35 a 445.22 a

LSD(0.05) 1.20 2.08 1.17

SE 0.58 1.01 0.58

Nitrogen (kg ha-1)

0 328.90 d 336.87 d 332.89 d

120 403.00 c 409.10 c 406.05 c

180 459.88 b 468.65 b 464.26 b

240 503.11 a 513.13 a 508.12 a

LSD(0.05) 0.92 1.09 0.71

SE 0.47 0.55 0.36


N×HA * * * (Fig. 29a)

N×G * * * (Fig. 29b)

HA×G * * * (Fig. 29c)

HA×G×N Ns * * (Fig. 29d)




127

Table 30. The effect of humic acid and nitrogen on thousand grain weight (g)

of maize genotypes


Genotypes

3025 253.61 b 257.02 b 255.32 b

55w65 270.80 a 277.05 a 273.93 a

Jalal 198.84 d 201.48 d 200.16 d

Iqbal 209.81 c 212.37 c 211.09 c

LSD(0.05) 2.68 1.74 1.42

SE 1.09 0.71 0.65


0 229.98 d 233.02 d 231.50 d

0.6 232.28 c 235.60 c 233.94 c

1.2 234.39 b 238.10 b 236.25 b

1.8 236.41 a 241.21 a 238.81 a

LSD(0.05) 0.92 1.00 0.66

SE 0.44 0.49 0.33

Nitrogen (kg ha-1)

0 214.91 d 221.25 d 218.08 d

120 228.65 c 231.72 c 230.19 c

180 239.35 b 242.68 b 241.01 b

240 250.16 a 252.27 a 251.22 a

LSD(0.05) 0.25 0.38 0.23

SE 0.12 0.19 0.11


N×HA * * * (Fig. 30a)

N×G * * * (Fig. 30b)

HA×G * * * (Fig. 30c)

HA×G×N * * * (Fig. 30d)




128

Figure 29a: Interaction between N×HA for grains ear-1 of maize. Vertical bars


Figure 29b: Interaction between N×G for grains ear-1 of maize. Vertical bars


Figure 29c: Interaction between HA×G for grains ear-1 of maize. Vertical bars


270

350

430

510

590

0 0.6 1.2 1.8

Gra

ins

ear

-1


N×HA

0

120

180

240

250

330

410

490

570

650

0 120 180 240

Gra

ins

ear

-1

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

330

380

430

480

530

0 0.6 1.2 1.8

Gra

ins

ear

-1


HA×G

3025

55w65

Jalal

Iqbal

129

Figure 29d: Interaction between G×HA×N for grains ear-1 of maize. Vertical bars


260

350

440

530

620

0 0.6 1.2 1.8

Gra

ins

ear

-1


3025 (HA×N)

0

120

180

240

260

350

440

530

620

0 0.6 1.2 1.8

Gra

ins

ear

-1


55w65 (HA×N)

0

120

180

240

260

350

440

530

620

0 0.6 1.2 1.8

Gra

ins

ear

-1


Jalal (HA×N)

0

120

180

240

260

350

440

530

620

0 0.6 1.2 1.8

Gra

ins

ear

-1


Iqbal (HA×N)

0

120

180

240

130

Figure 30a: Interaction between N×HA for 1000 grain weight (g) of maize. Vertical


Figure 30b: Interaction between N×G for 1000 grain weight (g) of maize. Vertical


Figure 30c: Interaction between HA×G for 1000 grain weight (g) of maize. Vertical


210

225

240

255

270

0 0.6 1.2 1.8

1000 g

rain

wei

gh

t (g

)


N×HA

0

120

180

240

170

210

250

290

330

0 120 180 240

1000 g

rain

wei

gh

t (g

)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

180

210

240

270

300

0 0.6 1.2 1.8

100

0 g

rain

wei

gh

t (g

)


HA×G

3025

55w65

Jalal

Iqbal

131

Figure 30d: Interaction between G×HA×N for 1000 grain weight (g) of maize.

Vertical bars represent standard error of mean in each

interaction.

170

200

230

260

290

320

0 0.6 1.2 1.8

10

00

gra

in w

eig

ht

(g)


3025 (HA×N)

0

140

180

240

170

200

230

260

290

320

0 0.6 1.2 1.8

1000 g

rain

wei

gh

t (g

)


55w65 (HA×N)

0

120

180

240

170

200

230

260

290

320

0 0.6 1.2 1.8

1000 g

rain

wei

gh

t (g

)


Jalal (HA×N)

0

120

180

140

170

200

230

260

290

320

0 0.6 1.2 1.8

10

00

gra

in w

eigh

t (g

)


Iqbal (HA×N)

0

120

180

240

132

4.4.11 Biological yield (kg ha-1)


years appreciably affected 1000 grain weight of maize (Table 31). All of the

interactions (G×HA, N×HA, G×N and G×HA×N) were found to be significant. Higher

biological yield was recorded in plots sown with 55w65 (18957 kg ha-1), followed by

genotype 3025 (17723 kg ha-1) while Iqbal variety produced lower biological yield

(12798 kg ha-1). Likewise, 1.8 kg ha-1 humic acid application provided higher biological

yield (16681 kg ha-1), followed by 1.2 kg HA ha-1 (16180 kg ha-1) while control plots

of humic acid (0 kg HA ha-1) produced lower biological yield (15241 kg ha-1).

Similarly, N application markedly affected biological yield of maize crop with its

increase from 0 to 240 kg ha-1. Higher BY (biological yield) was produced in treatments

supplemented with 240 kg N ha-1 (18648 kg ha-1), followed by 180 kg N ha-1 (17546

kg ha-1) while control experimental units of N provided minimum BY (12477 kg ha-1).

The N×HA interaction showed the substantial response of N to humic acid

application regarding biological yield of maize genotypes. However, 180 kg N ha-1

proved to be more responsive to the humic acid application against other N levels (Fig.

31a). The interaction of N×G suggested that biological yield of maize genotypes

enhanced linearly with the increase in N fertilizer. Hybrid 55w65 proved to be more

responsive in this respect when compared with other maize genotypes (Fig. 31b). The

HA×G interaction exhibited the significant response of maize genotypes to humic acid

application regarding their biological yield. Moreover, the plots sown with OPV Jalal

showed more response, although higher biological yield was recorded for 55w65 (Fig.

31c). The interaction G×HA×N indicated the well response of maize genotypes for

biological yield to various levels of humic acid and nitrogen. The genotype 55w65

responded considerably to the applied levels of humic acid and nitrogen when

compared with other maize genotypes. However, more response was observed at 120

kg N ha-1 under 1.8 kg HA ha-1 application (Fig. 31d).

4.4.12 Grain yield (kg ha-1)

Data statistical analysis indicated that genotypes, humic acid, nitrogen and years

substantially impacted maize grain yield (Table 32). All interactions were found to be

significant. Regarding genotypes, 55w65 produced higher grain yield (7597 kg ha-1),

followed by 3025 (6927 kg ha-1) while OPV Jalal proved inferior in grain yield (4784

kg ha-1). Similarly, humic acid application at the rate of 1.8 kg ha-1 produced higher

133

grain yield (6448 kg ha-1), followed by HA application at the rate of 1.2 kg ha-1 (6186

kg ha-1) while plots without HA (control) produced lower grain yield (5634 kg ha-1).

Furthermore; while considering N treatments, 240 kg ha-1 N provided higher maize

grain yield (7763 kg ha-1), followed by 180 kg ha-1 N (7014 kg ha-1) while control plots

of N (0 kg N ha-1) produced least grain yield (3855 kg ha-1).

The N×HA interaction revealed the well response of N fertilization to humic

acid application regarding grain yield of maize genotypes. Moreover, the plots supplied

with 240 kg ha-1 recorded higher grain yield, although more response to humic acid

application was shown at 120 kg N ha-1 (Fig. 32a). The interaction of N×G indicated

that grain yield of maize genotypes enhanced linearly with the increase in N fertilizer.

The hybrid 55w65 proved to be more responsive in this respect among maize genotypes

(Fig. 32b). The interaction of HA×G revealed the linear response of N for grain yield

in maize genotypes to humic acid application. Furthermore, the plots sown with hybrid

55w65 showed higher response and outyielded other maize genotypes (Fig. 32c). The

interaction G×HA×N indicated that the grain yield of maize genotypes increased with

the application of humic acid and N fertilizer in a significant way. However, the hybrid

55w65 exhibited more response to humic acid and N fertilization in comparison to other

maize genotypes. More response was observed at N application rate of 120 kg ha-1 at

1.8 kg HA ha-1 (Fig. 32d).

134

Table 31. The effect of humic acid and nitrogen on biological yield (kg ha-1) of

maize genotypes


Genotypes

3025 17627 b 17820 b 17723 b

55w65 18843 a 19071 a 18957 a

Jalal 14372 c 14551 c 14462 c

Iqbal 12677 d 12918 d 12798 d

LSD(0.05) 59.61 138.48 67.12

SE 24.36 56.59 30.81


0 15173 d 15309 d 15241 d

0.6 15701 c 15976 c 15838 c

1.2 16142 b 16217 b 16180 b

1.8 16503 a 16858 a 16681 a

LSD(0.05) 38.31 65.52 36.97

SE 18.56 31.75 18.39

Nitrogen (kg ha-1)

0 12281 d 12673 d 12477 d

120 15275 c 15262 c 15269 c

180 17402 b 17690 b 17546 b

240 18560 a 18736 a 18648 a

LSD(0.05) 28.60 46.25 27.02

SE 14.41 23.30 13.70


N×HA * * * (Fig. 31a)

N×G * * * (Fig. 31b)

HA×G * * * (Fig. 31c)

HA×G×N * * * (Fig. 31d)




135

Table 32. The effect of humic acid and nitrogen on grain yield (kg ha-1) of

maize genotypes


Genotypes

3025 6861 b 6993 b 6927 b

55w65 7530 a 7663 a 7597 a

Jalal 4698 d 4870 d 4784 d

Iqbal 4829 c 4962 c 4895 c

LSD(0.05) 47.42 91.26 46.58

SE 19.38 38.11 21.38


0 5575 d 5694 d 5634 d

0.6 5871 c 5999 c 5935 c

1.2 6119 b 6253 b 6186 b

1.8 6354 a 6543 a 6448 a

LSD(0.05) 30.40 38.53 23.91

SE 14.73 18.67 11.89

Nitrogen (kg ha-1)

0 3758 d 3952 d 3855 d

120 5507 c 5635 c 5571 c

180 6955 b 7073 b 7014 b

240 7699 a 7828 a 7763 a

LSD(0.05) 12.05 19.30 11.30

SE 6.07 9.72 5.73


N×HA * * * (Fig. 32a)

N×G * * * (Fig. 32b)

HA×G * * * (Fig. 32c)

HA×G×N * * * (Fig. 32d)




136

Figure 31a: Interaction between N×HA for biological yield (kg ha-1) of maize.


Figure 31b: Interaction between N×G for biological yield (kg ha-1) of maize. Vertical


Figure 31c: Interaction between HA×G for biological yield (kg ha-1) of maize.


11000

13500

16000

18500

21000

0 0.6 1.2 1.8

Bio

log

ical y

ield

(k

g h

a-1

)


N×HA

0

120

180

240

9000

13000

17000

21000

25000

0 120 180 240Bio

logic

al yie

ld (

kg h

a-1

)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

11000

14000

17000

20000

23000

0 0.6 1.2 1.8

Bio

log

ical y

ield

(k

g h

a-1

)


HA×G

3025

55w65

Jalal

Iqbal

137

Figure 31d: Interaction between G×HA×N for biological yield (kg ha-1) of maize.


8000

13000

18000

23000

28000

0 0.6 1.2 1.8

Bio

log

ical y

ield

(k

g h

a-1

)


3025 (HA×N)

0

120

180

240

8000

13000

18000

23000

28000

0 0.6 1.2 1.8

Bio

logic

al y

ield

(k

g h

a-1

)


55w65 (HA×N)

0

120

180

240

8000

13000

18000

23000

28000

0 0.6 1.2 1.8

Bio

logic

al yie

ld (

kg h

a-1

)


Jalal (HA×N)

0

120

180

240

8000

13000

18000

23000

28000

0 0.6 1.2 1.8

Bio

log

ical y

ield

(k

g h

a-1

)


Iqbal (HA×N)

0

120

180

240

138

Figure 32a: Interaction between N×HA for grain yield (kg ha-1) of maize. Vertical


Figure 32b: Interaction between N×G for grain yield (kg ha-1) of maize. Vertical bars


Figure 32c: Interaction between HA×G for grain yield (kg ha-1) of maize. Vertical


3000

4200

5400

6600

7800

9000

0 0.6 1.2 1.8

Gra

in y

ield

(k

g h

a-1

)


N×HA

0

120

180

240

2200

4200

6200

8200

10200

12200

0 120 180 240

Gra

in y

ield

(k

g h

a-1

)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

3800

4800

5800

6800

7800

8800

0 0.6 1.2 1.8

Gra

in y

ield

(k

g h

a-1

)


HA×G

3025

55w65

Jalal

Iqbal

139

Figure 32d: Interaction between G×HA×N for grain yield (kg ha-1) of maize.


2400

4400

6400

8400

10400

0 0.6 1.2 1.8

Gra

in y

ield

(k

g h

a-1

)


3025 (HA×N)

0

120

180

240

2400

4400

6400

8400

10400

0 0.6 1.2 1.8

Gra

in y

ield

(k

g h

a-1

)


55w65 (HA×N)

0

120

180

240

2400

4400

6400

8400

10400

0 0.6 1.2 1.8

Gra

in y

ield

(k

g h

a-1

)


Jalal (HA×N)

0

120

180

240

2400

4400

6400

8400

10400

0 0.6 1.2 1.8Gra

in y

ield

(k

g h

a-1

)


Iqbal (HA×N)

0

120

180

240

140

4.4.13 Stover yield (kg ha-1)

Statistical perusal of the data suggested that genotypes, humic acid, N fertilizer

and years significantly affected maize stover yield (Table 33). All interactions (N×HA,

G×N, HA×G and N×HA×G) were found significant. For maize genotypes, 55w65

produced higher stover yield (11360 kg ha-1), followed by hybrid 3025 (10796 kg ha-1)

while Iqbal variety produced lower stover yield (7902 kg ha-1). Likewise, humic acid

application at the rate of 1.8 kg ha-1 provided higher stover yield (10232 kg ha-1),

followed by HA application at the rate of 1.2 kg ha-1 (9994 kg ha-1) while plots without

humic acid (0 kg HA ha-1) resulted in lower stover yield (9606 kg ha-1). In a similar

way, 240 kg ha-1 N produced higher maize stover yield (10885 kg ha-1), followed by N

application of 180 kg ha-1 (10532 kg ha-1) while control plots (0 kg N ha-1) produced

lower stover yield (8622 kg ha-1).

The interaction of N×HA evaluated the substantial impact of humic acid on N

nutrient regarding stover yield of maize genotypes. However, the plots supplied with

180 kg N ha-1 provided more response to humic acid application regarding stover yield

as compared to other levels of N, although higher stover yield was recorded at 240 kg

N ha-1 (Fig. 33a). The interaction of N×G revealed the marked response of maize

genotypes in terms of stover yield to N levels. Moreover, the OPV Jalal exhibited higher

response in comparison to the remaining maize genotypes, although 55w65 produced

more stover yield (Fig. 33b). The interaction of HA×G revealed the responsive nature

of maize genotypes to the applications of humic acid as far as their stover yield is

concerned. The plots treated with OPV Jalal exhibited higher response to humic acid in

terms of stover yield against other genotypes, although more stover yield was recorded

by 55w65 (Fig. 33c). The interaction G×HA×N indicated the well response of maize

genotypes for stover yield to the applied levels of humic acid and N fertilizer. However,

55w65 proved superior in comparison to other maize genotypes. It showed more

response under 1.8 kg HA ha-1 at 120 kg ha-1 nitrogen (Fig. 33d).

4.4.14 Harvest Index (%)

Statistical analysis of the data revealed that genotypes, humic acid, N levels and

years significantly affected harvest index of maize (Table 34). The N×G and N×HA

and HA×G interactions were found to be significant. Regarding maize genotypes,

higher harvest index was reported in samples of hybrid 55w65 (39.37%), followed by

141

3025 (38.42%) while Jalal variety resulted in lower harvest index (32.57%). Similarly,

humic acid application at the rate of 1.8 kg ha-1 resulted in higher harvest index

(37.91%), followed by HA application of 1.2 kg ha-1 (37.43%) while lower harvest

index was produced in no humic acid treated plots (36.06%). Likewise, N application

of 240 kg ha-1 provided higher harvest index (41.36%), followed by 180 kg ha-1 N

(39.77%) while control plots of N proved to be inferior regarding HI of maize (30.73%).

The interaction N×HA showed that N fertilizer has a marked response to the

humic acid application regarding harvest index of maize genotypes. Moreover, the plots

supplemented with 120 kg ha-1 N produced higher response against humic acid in

comparison to other N levels (Fig. 34a). The interaction of N×G revealed the significant

response of harvest index in maize genotypes to the increase in N levels. The OPV Jalal

showed more response although 55w65 produced greater harvest index as compared to

other maize genotypes (Fig. 34b). The interaction HA×G suggested that harvest index

of maize genotypes was influenced in a linear way by the increase in humic acid. The

plots treated with 55w65 recorded higher harvest index as compared to other maize

genotypes, although Iqbal exhibited higher response (Fig. 34c). The interaction of

G×HA×N indicated the well response of maize genotypes for harvest index to the

increase in levels of humic acid and N nutrient. Moreover, the hybrid 55w65 superseded

other maize genotypes regarding the increase in harvest index. Best response was

studied at 180 kg N ha-1 under 1.8 kg HA ha-1, although higher HI was reported at 240

kg N ha-1 (Fig. 34d).

142

Table 33. The effect of humic acid and nitrogen on stover yield (kg ha-1) of

maize genotypes


Genotypes

3025 10766 b 10826 b 10796 b

55w65 11313 a 11408 a 11360 a

Jalal 9673 c 9681 c 9677 c

Iqbal 7848 d 7957 d 7902 d

LSD(0.05) 46.59 122.03 58.48

SE 19.86 49.87 26.84


0 9598 d 9615 d 9606 d

0.6 9831 c 9977 c 9904 c

1.2 10023 b 9964 b 9994 b

1.8 10148 a 10316 a 10232 a

LSD(0.05) 38.76 63.14 36.08

SE 18.78 30.59 17.95

Nitrogen (kg ha-1)

0 8523 d 8720 d 8622 d

120 9769 c 9626 c 9698 c

180 10448 b 10616 b 10532 b

240 10861 a 10908 a 10885 a

LSD(0.05) 29.38 51.39 29.41

SE 14.80 25.89 14.91


N×HA * * * (Fig. 33a)

N×G * * * (Fig. 33b)

HA×G * * * (Fig. 33c)

G×HA×N * * * (Fig. 33d)




143

Table 34. The effect of humic acid and nitrogen on harvest index (%) of maize

genotypes


Genotypes

3025 38.27 b 38.57 b 38.42 b

55w65 39.22 a 39.53 a 39.37 a

Jalal 32.12 d 33.02 d 32.57 d

Iqbal 37.48 c 37.86 c 37.68 c

LSD(0.05) 0.24 0.43 0.22

SE 0.10 0.18 0.10


0 35.80 d 36.31 d 36.06 d

0.6 36.52 c 36.75 c 36.64 c

1.2 37.07 b 37.78 b 37.43 b

1.8 37.69 a 38.13 a 37.91 a

LSD(0.05) 0.18 0.22 0.14

SE 0.09 0.11 0.07

Nitrogen (kg ha-1)

0 30.44 d 31.03 d 30.73 d

120 35.70 c 36.63 c 36.16 c

180 39.73 b 39.80 b 39.77 b

240 41.21 a 41.51 a 41.36 a

LSD(0.05) 0.10 0.17 0.10

SE 0.05 0.09 0.05


N×HA * * * (Fig. 34a)

N×G * * * (Fig. 34b)


G×HA×N * * * (Fig. 34d)




144

Figure 33a: Interaction between N×HA for stover yield (kg ha-1) of maize. Vertical


Figure 33b: Interaction between N×G for stover yield (kg ha-1) of maize. Vertical


Figure 33c: Interaction between HA×G for stover yield (kg ha-1) of maize. Vertical


8000

9000

10000

11000

12000

0 0.6 1.2 1.8

Sto

ver

yie

ld (

kg

ha

-1)


N×HA

0

120

180

240

6000

8000

10000

12000

14000

0 120 180 240

Sto

ver

yie

ld (

kg h

a-1

)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

7000

8500

10000

11500

13000

0 0.6 1.2 1.8

Sto

ver

yie

ld (

kg h

a-1

)


HA×G

3025

55w65

Jalal

Iqbal

145

Figure 33d: Interaction between G×HA×N for stover yield (kg ha-1) of maize.

Verticalbars represent standard error of mean in each interaction.

6000

8000

10000

12000

14000

0 0.6 1.2 1.8

Sto

ver

yie

ld (

kg

ha

-1)


3025 (HA×N)

0

120

180

240

6000

8000

10000

12000

14000

0 0.6 1.2 1.8Sto

ver

yie

ld (

kg

ha

-1)


55w65 (HA×N)

0

120

180

240

6000

8000

10000

12000

14000

0 0.6 1.2 1.8Sto

ver

yie

ld (

kg h

a-1

)


Jalal (HA×N)

0

120

180

240

6000

8000

10000

12000

14000

0 0.6 1.2 1.8Sto

ver

yie

ld (

kg

ha

-1)


Iqbal (HA×N)

0

120

180

240

146

Figure 34a: Interaction between N×HA for harvest index (%) of maize. Vertical bars


Figure 34b: Interaction between N×G for harvest index (%) of maize. Vertical bars


Figure 34c: Interaction between HA×G for harvest index (%) of maize. Vertical bars


28

32

36

40

44

0 0.6 1.2 1.8

Harv

est

ind

ex (

%)


N×HA

0

120

180

240

24

30

36

42

48

0 120 180 240

Harv

est

ind

ex (

%)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

30

33

36

39

42

0 0.6 1.2 1.8

Ha

rves

t in

dex

(%

)


HA×G

3025

55w65

Jalal

Iqbal

147

Figure 34d: Interaction between G×HA×N for harvest index (%) of maize. Vertical


26

31

36

41

46

0 0.6 1.2 1.8Ha

rves

t in

dex

(%

)


3025 (HA×N)

0

120

180

240

26

31

36

41

46

0 0.6 1.2 1.8

Harv

est

in

dex

(%

)


55w65 (HA×N)

0

120

180

240

26

31

36

41

46

0 0.6 1.2 1.8

Harv

est

ind

ex (

%)


Jalal (HA×N)

0

120

180

240

26

31

36

41

46

0 0.6 1.2 1.8

Ha

rv

est

in

dex

(%

)


Iqbal (HA×N)

0

120

180

240

148

4.4.15 NUE-AE (kg grains kg-1 N)

Analysis of variance indicated that all the factors (genotypes, humic acid and

nitrogen) significantly affected agronomic nitrogen use efficiency (NUE-AE) of maize

(Table 35). The HA×G, N×HA, G×N and N×HA×G interactions were found to be

significant. In maize genotypes, 55w65 resulted in higher NUE-AE (17.68 kg grains

kg-1 N), followed by 3025 (15.73 kg grains kg-1 N). The NUE-AE of OPVs Iqbal and

Jalal were lower (10.36 and 10.14 kg grains kg-1 N respectively). Likewise, humic acid

application at the rate of 1.8 kg ha-1 resulted in higher NUE-AE (15.50 kg grains kg-1

N), followed by humic acid application at the rate of 1.2 kg ha-1 (14.16 kg grains kg-1

N) while NUE-AE was lower in control plots of humic acid (11.37 kg grains kg-1 N).

Similarly, N application at the rate of 180 kg ha-1 provided higher NUE-AE (19.33 kg

grains kg-1 N), followed by 240 kg ha-1 N (17.62 kg grains kg-1 N) while lower NUE-

AE (16.97 kg grains kg-1 N) was recorded in plots supplied with 120 kg N ha-1.

Moreover, NUE-AE was nil (0 kg grains kg-1 N) in control plots of N.

The interaction N×HA showed the well response of N fertilizer regarding NUE-

AE in maize genotypes to the increase in humic acid. The plots treated with 120 kg ha-

1 N indicated more response regarding NUE-AE in maize genotypes (Fig. 35a). The

interaction of N×G revealed the significant response of NUE-AE in maize genotypes

to N application rates. The graphic trend of maize genotypes revealed that NUE-AE

increased by raising N levels from 0 to 180 kg ha-1, onward it showed a decrease with

the increase in N application. Moreover, higher response was observed for maize hybrid

55w65 in comparison to other maize genotypes (Fig. 35b). The interaction HA×G

indicated the substantial response of NUE-AE in maize genotypes to the increase in

humic acid application levels. The experimental units of 55w65 proved more promising

in this regard (Fig. 35c). The interaction of G×HA×N exhibited the significant response

of NUE-AE in maize genotypes to humic acid and N nutrient application levels.

However, 55w65 showed more NUE-AE in comparison to other maize genotypes. It

showed higher response at 120 kg N ha-1 under 1.8 kg HA ha-1 (Fig. 35d).

4.4.16 NUE-PFP (kg grains kg-1 N)

Analysis of variance indicated that genotypes, humic acid and nitrogen

appreciably influenced partial factor productivity nitrogen use efficiency (NUE-PFP)

of maize (Table 36). The HA×G, N×HA, G×N and N×HA×G interactions were

observed to be significant. The impact of years was found to be significant as a source

149

of variation. Regarding maize genotypes, the hybrid 55w65 provided higher NUE-PFP

(37.20 kg grains kg-1 N), followed by 3025 (33.81 kg grains kg-1 N) while OPV Jalal

resulted in lower NUE-PFP (23.11 kg grains kg-1 N). Similarly, 1.8 kg HA ha-1

produced higher NUE-PFP (31.46 kg grains kg-1 N), followed by humic acid

application at the rate of 1.2 kg ha-1 (30.11 kg grains kg-1 N) while lower NUE-PFP was

recorded in plots where no humic acid was applied (27.33 kg grains kg-1 N).

Furthermore, 120 kg N ha-1 produced greater NUE-PFP (46.42 kg grains kg-1 N),

followed by 180 kg ha-1 N (38.97 kg grains kg-1 N) while lower NUE-PFP was observed

in plots treated with 240 kg N ha-1 (32.35 kg grains kg-1 N). On the other hand, NUE-

PFP was nil (0 kg grains kg-1 N) in control plots of nitrogen.

The interaction of N×HA revealed the linear response of N fertilizer to the

increase of humic acid regarding NUE-PFP in maize genotypes. The plots treated with

120 kg ha-1 N exhibited more NUE-PFP against other N levels (Fig. 36a). The

interaction of N×G showed the well response of NUE-PFP in maize genotypes to N

application levels. It was shown that NUE-PFP of maize genotypes enhanced in a linear

fashion by raising N levels from 0 to 120 kg ha-1, afterwards it exhibited a downward

trend. Maize hybrid 55w65 proved superior in this regard in comparison to other maize

genotypes (Fig. 36b). The interaction HA×G indicated the substantial response of maize

genotypes in terms of NUE-PFP to the increase in humic acid. Moreover, the hybrid

55w65 exhibited higher NUE-PFP as compared to other maize genotypes (Fig. 36c).

The interaction G×HA×N revealed the significant response of NUE-PFP in maize

genotypes to the increase in humic acid and N fertilizer. However, 55w65 showed

higher NUE-PFP in comparison to other maize genotypes at 120 kg N ha-1 under 1.8

kg HA ha-1 (Fig. 36d).

150

Table 35. The effect of humic acid and nitrogen on NUE-AE (kg grains kg-1

N) of maize genotypes


Genotypes

3025 15.57 b 15.89 b 15.73 b

55w65 17.80 a 17.57 a 17.68 a

Jalal 10.27 c 10.00 c 10.14 c

Iqbal 10.32 c 10.41 c 10.36 c

LSD(0.05) 0.49 0.77 0.41

SE 0.20 0.32 0.17


0 11.40 d 11.34 d 11.37 d

0.6 12.92 c 12.84 c 12.88 c

1.2 14.19 b 14.13 b 14.16 b

1.8 15.45 a 15.56 a 15.50 a

LSD(0.05) 0.19 0.29 0.17

SE 0.09 0.14 0.08

Nitrogen (kg ha-1)

0 0.00 d 0.00 d 0.00 d

120 16.98 c 16.96 c 16.97 c

180 19.36 a 19.30 a 19.33 a

240 17.62 b 17.61 b 17.62 b

LSD(0.05) 0.06 0.10 0.06

SE 0.03 0.05 0.03


N×HA * * * (Fig. 35a)

N×G * * * (Fig. 35b)

HA×G * * * (Fig. 35c)

G×HA×N * * * (Fig. 35d)




151

Table 36. The effect of humic acid and nitrogen on NUE-PFP (kg grains kg-1

N) of maize genotypes


Genotypes

3025 33.47 b 34.15 b 33.81 b

55w65 37.04 a 37.36 a 37.20 a

Jalal 22.77 d 23.45 c 23.11 d

Iqbal 23.33 c 23.91 c 23.62 c

LSD(0.05) 0.30 0.60 0.30

SE 0.12 0.25 0.14


0 27.06 d 27.59 d 27.33 d

0.6 28.58 c 29.09 c 28.83 c

1.2 29.85 b 30.38 b 30.11 b

1.8 31.11 a 31.81 a 31.46 a

LSD(0.05) 0.17 0.24 0.14

SE 0.08 0.12 0.07

Nitrogen (kg ha-1)

0 0.00 d 0.00 d 0.00 d

120 45.89 a 46.96 a 46.42 a

180 38.64 b 39.30 b 38.97 b

240 32.08 c 32.62 c 32.35 c

LSD(0.05) 0.06 0.10 0.06

SE 0.03 0.05 0.03


N×HA * * * (Fig. 36a)

N×G * * * (Fig. 36b)

HA×G * * * (Fig. 36c)

G×HA×N * * * (Fig. 36d)




152

Figure 35a: Interaction between N×HA for NUE-AE (kg grains kg-1 N) of maize.


Figure 35b: Interaction between N×G for NUE-AE (kg grains kg-1 N) of maize.


Figure 35c: Interaction between HA×G for NUE-AE (kg grains kg-1 N) of maize.


0

5

10

15

20

25

0 0.6 1.2 1.8

NU

E-A

E

(kg

gra

ins

kg

-1N

)


N×HA

0

120

180

240

0

10

20

30

40

0 120 180 240

NU

E-A

E

(kg g

rain

s k

g-1

N)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

7

10

13

16

19

22

0 0.6 1.2 1.8

NU

E-A

EA

(kg

gra

ins

kg

-1N

)


HA×G

3025

55w65

Jalal

Iqbal

153

Figure 35d: Interaction between G×HA×N for NUE-AE (kg grains kg-1 N) of maize.


0

5

10

15

20

25

30

0 0.6 1.2 1.8

NU

E-A

E

(kg

gra

ins

kg

-1N

)


3025 (HA×N)

0

120

180

240

0

5

10

15

20

25

30

0 0.6 1.2 1.8

NU

E-A

E

(kg g

rain

s k

g-1

N)


55w65 (HA×N)

0

120

180

240

0

5

10

15

20

25

30

0 0.6 1.2 1.8

NU

E-A

E

(kg g

rain

s k

g-1

N)


Jalal (HA×N)

0

120

180

240

0

5

10

15

20

25

30

0 0.6 1.2 1.8

NU

E-A

E

(kg

gra

ins

kg

-1N

)


Iqbal (HA×N)

0

120

180

240

154

Figure 36a: Interaction between N×HA for NUE-PFP (kg grains kg-1 N) of maize.


Figure 36b: Interaction between N×G for NUE-PFP (kg grains kg-1 N) of maize.


Figure 36c: Interaction between HA×G for NUE-PFP (kg grains kg-1 N) of maize.


0

12

24

36

48

60

0 0.6 1.2 1.8

NU

E-P

FP

(kg g

rain

s k

g-1

N)


N×HA

0

120

180

240

0

18

36

54

72

90

0 120 180 240

NU

E-P

FP

(kg g

rain

s k

g-1

N)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

20

25

30

35

40

45

0 0.6 1.2 1.8

NU

E-P

FP

(kg

gra

ins

kg

-1N

)


HA×G

3025

55w65

Jalal

Iqbal

155

Figure 36d: Interaction between G×HA×N for NUE-PFP (kg grains kg-1 N) of

maize. Vertical bars represent standard error of mean in each interaction.

0

15

30

45

60

75

0 0.6 1.2 1.8

NU

E-P

FP

(kg

gra

ins

kg

-1N

)


3025 (HA×N)

0

120

180

240

0

15

30

45

60

75

0 0.6 1.2 1.8

NU

E-P

FP

(kg g

rain

s k

g-1

N)


55w65 (HA×N)

0

120

180

240

0

15

30

45

60

75

0 0.6 1.2 1.8

NU

E-P

FP

(kg g

rain

s k

g-1

N)


Jalal (HA×N)

0

120

180

240

0

15

30

45

60

75

0 0.6 1.2 1.8

NU

E-P

FP

(kg

gra

ins

kg

-1N

)


Iqbal (HA×N)

0

120

180

240

156

4.4.17 NAR (30-75 DAS) (g m-2 day-1)

Statistical analysis of the data exhibited that genotypes, humic acid, nitrogen

and years significantly affected maize net assimilation rate (30-75 DAS) (Table 37).

The interactions of N×G, N×HA, HA×G and N×HA×G were reported to be significant.

Regarding genotypes, higher NAR was calculated for OPV Iqbal (11.91 g m-2 day-1),

followed by 55w65 genotype (11.42 g m-2 day-1) while NAR was lower in samples

collected from plots of Jalal variety (9.57 g m-2 day-1). Likewise, humic acid application

at the rate of 1.8 kg ha-1 produced higher NAR (11.17 g m-2 day-1), followed by HA

application of 1.2 kg ha-1 (11.06 g m-2 day-1) while lower NAR was recorded in plots

where no HA was applied (10.84 g m-2 day-1). In a similar way, 240 kg ha-1 N provided

higher NAR (11.80 g m-2 day-1), followed by 180 kg N ha-1 (11.45 g m-2 day-1) while

lower NAR was calculated in control plots of N fertilizer (9.75 g m-2 day-1).

The interaction N×HA identified the marked response of of N for NAR in maize

genotypes to the increase of humic acid. The treatments of 240 kg ha-1 N provided more

NAR as compared to other levels of N (Fig. 37a). The interaction of N×G indicated the

well response of NAR in maize genotypes to the increase in levels of N. The Iqbal

cultivar of maize provided higher NAR against other maize genotypes (Fig. 37b). The

interaction of HA×G suggested the significant response of NAR in maize genotypes to

the increase in humic acid. The Iqbal variety of maize produced substantially higher

NAR as compared to other maize genotypes (Fig. 37c). The interaction G×HA×N

exhibited the significant response of NAR in maize genotypes to the increase in humic

acid and N fertilizer. However, the OPV Iqbal recorded significantly higher NAR in

comparison to other maize genotypes at 240 kg N ha-1 under 1.8 kg HA ha-1 (Fig. 37d).

4.4.18 Grain protein (%)

Statistical perusal of the data revealed that genotypes, humic acid and nitrogen

fertilizer significantly affected grain protein (%) of maize (Table 38). All interactions

of N×HA, N×G, HA×G and N×HA×G were observed to be significant. The effect of

years was also significant as a source of variation. Regarding genotypes, grain protein

content was higher in samples collected from plots sown with Iqbal variety (9.62%),

followed by Jalal (9.36%) while it was lower in samples of 55w65 plots (6.82%).

Likewise, plots treated with 1.8 kg ha-1 humic acid resulted in higher grain protein

(8.49%), followed by application of 1.2 kg ha-1 humic acid (8.29%) while it was lower

157

in plots where no humic acid was applied (7.98%). Additionally, N application of 240

kg ha-1 produced higher grain protein content (8.62%), followed by 180 kg ha-1 N

(8.40%) while plots without N application produced plants with reduced protein content

(7.78%).

The interaction N×HA exhibited the well response of N levels to the increase in

humic acid regarding the grain protein (%) of maize genotypes. The plots supplied with

240 kg ha-1 N responded in a well manner to the applications of humic acid in

comparison to other N levels (Fig. 38a). The interaction of N×G showed the linear

response of grain protein (%) in maize genotypes to the N fertilization. However, the

OPV Iqbal proved superior in this regard as compared to other genotypes (Fig. 38b).

The interaction HA×G suggested that the grain protein content of maize genotypes

enhanced in a linear way with the increase in humic acid. Furthermore, the plots treated

with OPVs Iqbal and Jalal showed higher protein content as compared to other maize

genotypes (Fig. 38c). The interaction of G×HA×N revealed that protein content of

maize genotypes responded linearly to the application of humic acid and N fertilizer.

The OPV Iqbal exhibited greater protein content in relation to other maize genotypes

(Fig. 38d).

158

Table 37. The effect of humic acid and nitrogen on net assimilation rate (g m-

2 day-1) of maize genotypes


Genotypes

3025 11.09 c 11.15 c 11.12 c

55w65 11.37 b 11.48 b 11.42 b

Jalal 9.52 d 9.62 d 9.57 d

Iqbal 11.85 a 11.96 a 11.91 a

LSD(0.05) 0.09 0.10 0.06

SE 0.04 0.04 0.03


0 10.81 d 10.87 d 10.84 d

0.6 10.91 c 10.98 c 10.94 c

1.2 11.01 b 11.11 b 11.06 b

1.8 11.09 a 11.25 a 11.17 a

LSD(0.05) 0.04 0.04 0.03

SE 0.02 0.02 0.01

Nitrogen (kg ha-1)

0 9.68 d 9.81 d 9.75 d

120 10.98 c 11.06 c 11.02 c

180 11.40 b 11.50 b 11.45 b

240 11.76 a 11.84 a 11.80 a

LSD(0.05) 0.02 0.03 0.01

SE 0.01 0.01 0.01


N×HA * * * (Fig. 37a)

N×G * * * (Fig. 37b)


G×HA×N * * * (Fig. 37d)




159

Table 38. The effect of humic acid and nitrogen on grain protein (%) of maize

genotypes


Genotypes

3025 7.06 c 7.14 c 7.10 c

55w65 6.75 d 6.89 d 6.82 d

Jalal 9.26 b 9.46 b 9.36 b

Iqbal 9.55 a 9.69 a 9.62 a

LSD(0.05) 0.06 0.06 0.04

SE 0.03 0.02 0.02


0 7.88 d 8.08 d 7.98 d

0.6 8.08 c 8.20 c 8.14 c

1.2 8.23 b 8.35 b 8.29 b

1.8 8.44 a 8.55 a 8.49 a

LSD(0.05) 0.06 0.03 0.03

SE 0.03 0.02 0.02

Nitrogen (kg ha-1)

0 7.71 d 7.84 d 7.78 d

120 8.02 c 8.18 c 8.10 c

180 8.33 b 8.47 b 8.40 b

240 8.56 a 8.69 a 8.62 a

LSD(0.05) 0.06 0.02 0.03

SE 0.03 0.01 0.02


N×HA * * * (Fig. 38a)

N×G * * * (Fig. 38b)


G×HA×N Ns * * (Fig. 38d)




160

Figure 37a: Interaction between N×HA for NAR (30-75 DAS) (g m-2 day-1) of


Figure 37b: Interaction between N×G for NAR (30-75 DAS) (g m-2 day-1) of maize.


Figure 37c: Interaction between HA×G for NAR (30-75 DAS) (g m-2 day-1) of

maize. Vertical bars represent error of mean in each interaction.

9

10

11

12

13

0 0.6 1.2 1.8

Net

ass

imil

ati

on

ra

te

(g m

-2d

ay

-1)


N×HA

0

120

180

240

8

9

10

11

12

13

0 120 180 240

Net

ass

imil

ati

on

rate

(g m

-2d

ay

-1)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

9

10

11

12

13

0 0.6 1.2 1.8

Net

ass

imil

ati

on

rate

(g m

-2d

ay

-1)


HA×G

3025

55w65

Jalal

Iqbal

161

Figure 37d: Interaction between G×HA×N for NAR (30-75 DAS) (g m-2 day-1) of


8

10

12

14

0 0.6 1.2 1.8

Net

ass

imil

ati

on

ra

te

(g m

-2d

ay

-1)


3025 (HA×N)

0

120

180

240

8

10

12

14

0 0.6 1.2 1.8

Net

ass

imil

ati

on

ra

te

(g m

-2 d

ay

-1)


55w65 (HA×N)

0

120

180

240

89

1011121314

0 0.6 1.2 1.8

Net

ass

imil

ati

on

rate

(g m

-2d

ay

-1)


Jalal (HA×N)

0

120

180

240

8

9

10

1112

13

14

0 0.6 1.2 1.8

Net

ass

imil

ati

on

rate

(g m

-2d

ay

-1)


Iqbal (HA×N)

0

120

180

240

162

Figure 38a: Interaction between N×HA for grain protein content (%) of maize.


Figure 38b: Interaction between N×G for grain protein content (%) of maize.


7.4

7.9

8.4

8.9

9.4

0 0.6 1.2 1.8

Gra

in p

rote

in (

%)


N×HA

0

120

180

240

6.0

7.0

8.0

9.0

10.0

11.0

0 120 180 240

Gra

in p

rote

in (

%)

N levels (kg ha-1)

N×G

3025

55w65

Jalal

Iqbal

163

Figure 38c: Interaction between HA×G for grain protein content (%) of maize.


Figure 38d: Interaction between G×HA×N for grain protein content (%) of maize.


6

7

8

9

10

11

0 0.6 1.2 1.8

Gra

in p

rote

in (

%)


3025 (HA×N)

0

120

180

240 6

7

8

9

10

11

0 0.6 1.2 1.8

Gra

in p

rote

in (

%)


55w65 (HA×N)

0

120

180

240

6

7

8

9

10

11

0 0.6 1.2 1.8

Gra

in p

rote

in (

%)


Jalal (HA×N)

0

120

180

240 6

7

8

9

10

11

0 0.6 1.2 1.8

Gra

in p

roti

en (

%)


Iqbal (HA×N)

0

120

180

240

6.0

7.0

8.0

9.0

10.0

11.0

0 0.6 1.2 1.8

Gra

in p

rote

in (

%)


HA×G

3025

55w65

Jalal

Iqbal

164


4.5.1 Soil phosphorous content (mg kg-1) at maize harvest

Statistical analysis of the data showed that genotypes, humic acid and N

fertilization considerably impacted soil phosphorous (P) content at maize harvest

(Table 39). The interaction HA×G interaction was found to be significant. The effect

of years was also observed to be significant as a source of variation. Regarding maize

genotypes, soil P content was higher in samples collected from plots sown with Iqbal

variety (6.20 mg kg-1), followed by Jalal cultivar (6.16 mg kg-1) while it was lower in

samples collected from plots sown with maize hybrid 55w65 (6.09 mg kg-1). Regarding

humic acid treatments, plots treated with 1.8 kg ha-1 humic acid produced higher soil P

content (8.36 mg kg-1), followed by the application of 1.2 kg ha-1 humic acid (7.29 mg

kg-1) while soil P content was lower in control plots of humic acid (3.64 mg kg-1).

Moreover, N application of 240 kg ha-1 provided higher soil P content (6.18 mg kg-1),

followed by 180 kg ha-1 N (6.15 mg kg-1) while lower soil P content was recorded in

control plots of N (6.04 mg kg-1).

The interaction of HA×G indicated that maize genotypes had a linear response

to the humic acid applications regarding P content of the soil at maize harvest. The plots

sown with Iqbal cultivar exhibited higher soil P content in relation to other maize

genotypes (Fig. 39a).

4.40 Soil nitrogen content (%) at maize harvest

Statistical analysis of the data indicated that genotypes, humic acid and nitrogen

substantially impacted soil N content (%) at maize harvest (Table 40). The interaction

of HA×G was found to be significant. The effect of years was also reported to be

significant as a source of variation. Regarding maize genotypes, soil N content was

higher in plots treated with OPV Iqbal at maize harvest (0.057%), followed by Jalal

(0.056%) while soil N content was lower in plots sown with hybrid 55w65 (0.52%).

Similarly, plots treated with 1.8 kg ha-1 humic acid produced higher soil N content

(0.072%), followed by 1.2 kg ha-1 humic acid (0.061%) while soil N was lower in plots

where no humic acid was applied (0.036%). Moreover, N application (240 kg ha-1)

provided higher soil N content (0.057%), followed by 180 kg ha-1 N (0.056%) while

lower soil N was recorded in control plots of N (0.051%).

165

The interaction of HA×G indicated that maize genotypes have linear response

to the application of humic acid regarding N content of the soil. The plots sown with

Iqbal cultivar exhibited higher soil N content in relation to other maize genotypes (Fig.

40a).

Table 39. The effect of maize genotypes, humic acid and nitrogen on

phosphorous (P) content (mg kg-1) of soil at maize harvest


Genotypes

3025 6.04 c 6.14 c 6.09 c

55w65 5.99 d 6.05 d 6.02 d

Jalal 6.11 b 6.20 b 6.16 b

Iqbal 6.17 a 6.23 a 6.20 a

LSD(0.05) 0.05 0.02 0.02

SE 0.02 0.01 0.01


0 3.60 d 3.68 d 3.64 d

0.6 5.14 c 5.22 c 5.18 c

1.2 7.25 b 7.32 b 7.29 b

1.8 8.32 a 8.40 a 8.36 a

LSD(0.05) 0.03 0.01 0.01

SE 0.01 0.01 0.01

Nitrogen (kg ha-1)

0 6.00 d 6.08 d 6.04 d

120 6.07 c 6.13 c 6.10 c

180 6.10 b 6.19 b 6.15 b

240 6.14 a 6.22 a 6.18 a

LSD(0.05) 0.03 0.01 0.01

SE 0.01 0.01 0.01


N×HA Ns Ns Ns

N×G Ns Ns Ns

HA×G * * * (Fig. 39a)

G×HA×N Ns Ns Ns




166

Table 40. The effect of maize genotypes, humic acid and nitrogen on N content

(%) of soil at maize harvest


Genotypes

3025 0.054 c 0.055 c 0.055 c

55w65 0.051 d 0.052 d 0.052 d

Jalal 0.055 b 0.056 b 0.056 b

Iqbal 0.057 a 0.058 a 0.057 a

LSD(0.05) 0.001 0.002 0.001

SE 0.001 0.001 0.001


0 0.036 d 0.037 d 0.036 d

0.6 0.050 c 0.051 c 0.051 c

1.2 0.060 b 0.061 b 0.061 b

1.8 0.071 a 0.072 a 0.072 a

LSD(0.05) 0.001 0.001 0.001

SE 0.001 0.001 0.001

Nitrogen (kg ha-1)

0 0.049 d 0.051 d 0.050 d

120 0.054 c 0.055 c 0.054 c

180 0.055 b 0.056 b 0.056 b

240 0.056 a 0.057 a 0.057 a

LSD(0.05) 0.001 0.001 0.001

SE 0.001 0.001 0.001


N×HA Ns Ns Ns

N×G Ns Ns Ns

HA×G * * * (Fig. 40a)

G×HA×N Ns Ns Ns




167

Figure 39a: Interaction between N×HA for soil P content (mg kg-1) at maize harvest.


Figure 40a: Interaction between HA×G for soil N content (%) at maize harvest.


2.5

4.0

5.5

7.0

8.5

10.0

0 0.6 1.2 1.8

So

il p

ho

sph

oro

us

(P)

con

ten

t

(mg

kg

-1)

at

ma

ize

ha

rves

t


N×HA

3025

55w65

Jalal

Iqbal

0.02

0.04

0.06

0.08

0.10

0 0.6 1.2 1.8

Soil

nit

rog

en (

N)

con

ten

t

(%)

at

maiz

e h

arv

est


HA×G

3025

55w65

Jalal

Iqbal

168

4.5.3 Soil organic matter (%) at maize harvest

Statistical analysis of the data indicated that nitrogen fertilizer, humic acid,

maize genotypes and years significantly affected soil organic matter (%) at maize

harvest (Table 41). The interactions N×HA and HA×G were reported to be significant.

Regarding genotypes, soil organic matter was higher in samples collected from plots

sown with Iqbal cultivar (0.88%), followed by Jalal cultivar (0.85%) while it was lower

in samples of 55w65 and 3025 plots (0.83%). Similarly, plots treated with 1.8 kg ha-1

humic acid resulted in higher soil organic matter content (1.17%), followed by the

application of 1.2 kg ha-1 humic acid (1.05%) while soil organic matter was lower in

control plots of humic acid (0 kg HA ha-1) (0.26%). Accordingly, plots treated with 240

kg ha-1 N provided higher soil organic matter content (0.86%) which was at par with

other N levels while control plots of N provided lower soil organic matter (0.82%).

The interaction of N×HA revealed the significant nature of N fertilizer against

the applications of humic acid regarding the organic matter (%) of soil at maize harvest.

Moreover, a substantial increase in soil organic matter was recorded for OPV Iqbal in

comparison to other maize genotypes (Fig. 41a). The interaction of HA×G

demonstrated the linear response of maize genotypes to humic acid application in terms

of organic matter (%) of the soil. The plots sown with maize cultivar Iqbal exhibited a

higher trend of increase for organic matter of the soil in relation to other genotypes (Fig.

41b).


Data pertaining to economic analysis of maize genotypes as affected by humic

acid and N application rates (Table 42). Among the maize genotypes, higher net income

(NI) (2012 US$) was obtained for G3H3N3 treatment combination, followed by

G2H2N3 (1964 US$) while the lowest net income (568 US$) was attained in case of

treatment combination of G4H0N0. Likewise, the higher value cost ratio (VCR) of 7.75

was achieved for treatment combination of G2H0N2, followed by G2H3N2 (7.49) and

G2H2N2 (7.45), while the lower VCR (2.64) was recorded in case of G3H0N1

treatment combination.

169

Table 41. The effect of maize genotypes, humic acid and nitrogen on organic

matter (%) of soil at maize harvest


Genotypes

3025 0.81 c 0.85 d 0.83 c

55w65 0.80 d 0.86 c 0.83 c

Jalal 0.83 b 0.87 b 0.85 b

Iqbal 0.85 a 0.89 a 0.87 a

LSD(0.05) 0.01 0.01 0.01

SE 0.01 0.01 0.01


0 0.26 d 0.26 d 0.26 d

0.6 0.89 c 0.93 c 0.91 c

1.2 1.02 b 1.07 b 1.04 b

1.8 1.13 a 1.22 a 1.17 a

LSD(0.05) 0.01 0.01 0.01

SE 0.01 0.01 0.01

Nitrogen (kg ha-1)

0 0.80 d 0.84 d 0.82 a

120 0.82 c 0.86 c 0.84 b

180 0.83 b 0.88 b 0.85 b

240 0.84 a 0.89 a 0.86 b

LSD(0.05) 0.01 0.01 0.02

SE 0.01 0.01 0.01


N×HA * * * (Fig. 41a)

N×G Ns Ns Ns

HA×G * Ns * (Fig. 41b)

G×HA×N Ns Ns Ns




170

Figure 41a: Interaction between N×HA for soil organic matter (%) at maize harvest.


Figure 41b: Interaction between HA×G for soil organic matter (%) at maize harvest.


0.0

0.3

0.6

0.9

1.2

1.5

0 0.6 1.2 1.8

Soil

org

an

ic m

att

er (

%)

at

maiz

e h

arv

est


N×HA

0

120

180

240

0.0

0.3

0.6

0.9

1.2

1.5

0 0.6 1.2 1.8

So

il o

rga

nic

matt

er (

%)

at

maiz

e h

arv

est


HA×G

3025

55w65

Jalal

Iqbal

171

Table 42. Economic analysis of integration of humic acid with nitrogen in terms of

US$ during 2014 and 2015.

Treat-

ment

HA

cost

ha-1

N

cost

ha-1

Seed

cost

ha-1

Variab

le cost

Total

cost

Grain

value

@

US$

0.21

kg-1

Stover

value

@

US$

28.63

t-1

Gross

incom

e

(US$)

Net

inco-

me

(US$)

Gross

return

over

control

( ha-1)

VCR

(value

cost

ratio)

A B C D=A+

B+C

E=

D+fix.

Cost

F G H=F+

G

I=H-

E

J J/A+B

G1H0N0 0 0.0 77.3 77.3 312 841 265 1106 794 - -

G1H0N1 0 69.7 77.3 147.0 382 1238 292 1530 1149 355 5.09

G1H0N2 0 104.6 77.3 181.9 417 1574 316 1889 1473 679 6.49

G1H0N3 0 139.4 77.3 216.7 452 1802 327 2129 1677 883 6.34

G1H1N0 12.4 0.0 77.3 89.7 324 888 272 1159 835 41 3.29

G1H1N1 12.4 69.7 77.3 159.4 394 1311 300 1610 1216 422 5.14

G1H1N2 12.4 104.6 77.3 194.3 429 1649 325 1974 1545 751 6.42

G1H1N3 12.4 139.4 77.3 229.1 464 1852 337 2188 1724 930 6.13

G1H2N0 21.0 0.0 77.3 98.3 333 942 269 1212 879 85 4.03

G1H2N1 21.0 69.7 77.3 168.0 403 1388 307 1695 1292 498 5.49

G1H2N2 21.0 104.6 77.3 202.9 438 1712 328 2040 1603 809 6.44

G1H2N3 21.0 139.4 77.3 237.7 472 1897 338 2235 1763 969 6.04

G1H3N0 29.6 0.0 77.3 106.9 342 986 274 1260 918 124 4.20

G1H3N1 29.6 69.7 77.3 176.6 411 1478 317 1795 1384 590 5.94

G1H3N2 29.6 104.6 77.3 211.5 446 1766 334 2100 1654 860 6.41

G1H3N3 29.6 139.4 77.3 246.3 481 1947 345 2292 1811 1017 6.02

G2H0N0 0 0.0 81.1 81.1 316 908 272 1180 864 - -

G2H0N1 0 69.7 81.1 150.8 386 1334 301 1635 1249 385 5.53

G2H0N2 0 104.6 81.1 185.7 420 1754 341 2095 1674 810 7.75

G2H0N3 0 139.4 81.1 220.5 455 1990 355 2346 1890 1026 7.36

G2H1N0 12.4 0.0 81.1 93.5 328 952 275 1227 899 35 2.81

G2H1N1 12.4 89.6 81.1 183.2 418 1431 311 1742 1325 461 4.51

G2H1N2 12.4 134.4 81.1 228.0 463 1819 351 2170 1708 844 5.74

G2H1N3 12.4 179.3 81.1 272.8 508 2039 359 2398 1891 1027 5.36

172

G2H2N0 21.0 0.0 81.1 102.1 337 1007 271 1279 942 78 3.71

G2H2N1 21.0 69.7 81.1 171.8 407 1530 319 1850 1443 579 6.38

G2H2N2 21.0 104.6 81.1 206.7 441 1890 351 2241 1800 936 7.45

G2H2N3 21.0 139.4 81.1 241.5 476 2084 356 2440 1964 1100 6.86

G2H3N0 29.6 0.0 81.1 110.7 345 1065 276 1341 995 131 4.44

G2H3N1 29.6 69.7 81.1 180.4 415 1635 330 1965 1549 685 6.90

G2H3N2 29.6 104.6 81.1 215.3 450 1951 368 2319 1869 1005 7.49

G2H3N3 29.6 139.4 81.1 250.1 485 2131 366 2497 2012 1148 6.79

G3H0N0 0 0.0 13.4 13.4 248 603 231 835 587 - -

G3H0N1 0 69.7 13.4 83.1 318 828 261 1089 771 184 2.64

G3H0N2 0 104.6 13.4 117.9 353 1055 269 1324 971 384 3.68

G3H0N3 0 139.4 13.4 152.8 388 1223 292 1515 1127 540 3.88

G3H1N0 12.4 0.0 13.4 25.8 261 644 238 881 621 34 2.73

G3H1N1 12.4 69.7 13.4 95.5 330 880 268 1148 818 231 2.81

G3H1N2 12.4 104.6 13.4 130.3 365 1157 294 1452 1087 500 4.27

G3H1N3 12.4 139.4 13.4 165.2 400 1265 305 1569 1169 582 3.84

G3H2N0 21.0 0.0 13.4 34.4 269 677 243 920 651 64 3.04

G3H2N1 21.0 69.7 13.4 104.1 339 938 273 1211 872 285 3.14

G3H2N2 21.0 104.6 13.4 138.9 374 1197 300 1496 1123 536 4.27

G3H2N3 21.0 139.4 13.4 173.8 409 1307 312 1619 1211 624 3.89

G3H3N0 29.6 0.0 13.4 42.9 278 711 251 961 684 97 3.27

G3H3N1 29.6 69.7 13.4 112.7 347 996 276 1271 924 337 3.39

G3H3N2 29.6 104.6 13.4 147.5 382 1246 306 1552 1170 583 4.34

G3H3N3 29.6 139.4 13.4 182.4 417 1346 316 1662 1245 658 3.89

G4H0N0 0 0.0 13.4 13.4 248 617 199 816 568 - -

G4H0N1 0 69.7 13.4 83.1 318 853 218 1071 753 185 2.66

G4H0N2 0 104.6 13.4 117.9 353 1077 225 1302 949 381 3.65

G4H0N3 0 139.4 13.4 152.8 388 1231 238 1469 1081 513 3.68

G4H1N0 12.4 0.0 13.4 25.8 261 674 201 875 615 47 3.76

G4H1N1 12.4 69.7 13.4 95.5 330 905 223 1128 798 230 2.80

G4H1N2 12.4 104.6 13.4 130.3 365 1197 234 1432 1067 499 4.26

G4H1N3 12.4 139.4 13.4 165.2 400 1274 244 1518 1118 550 3.62

173

G4H2N0 21.0 0.0 13.4 34.4 269 699 203 902 633 65 3.07

G4H2N1 21.0 69.7 13.4 104.1 339 958 222 1180 841 273 3.01

G4H2N2 21.0 104.6 13.4 138.9 374 1234 240 1474 1100 532 4.24

G4H2N3 21.0 139.4 13.4 173.8 409 1320 245 1564 1156 588 3.66

G4H3N0 29.6 0.0 13.4 42.9 278 738 209 948 670 102 3.44

G4H3N1 29.6 69.7 13.4 112.7 347 1012 225 1237 889 321 3.23

G4H3N2 29.6 104.6 13.4 147.5 382 1285 243 1528 1145 577 4.30

G4H3N3 29.6 139.4 13.4 182.4 417 1372 252 1624 1206 638 3.78

HA cost ha-1 = Cost of humic acid @ 0.028 US$ L-1 of 2000 ppm humic acid solution +

3.81 US$ ha-1 as application charges.

N cost ha-1 = Cost of nitrogen @ 0.58 US$ kg-1 + 7.63 US$ ha-1 as top dressing application

charges of N in two split doses.

In addition 234.77 US$ ha-1 as fixed charges (seedbed preparation, cost of basal dose of P

at seedbed preparation, plantation charges, irrigations, weedicide, plant protection charges

plus labour used for various operations).

174

5. DISCUSSION

The results derived from our studies shown that humic acid (organically charged

biostimulant and a chelating agent) in integration with N considerably improved yield

and yield components of maize genotypes under the agro-climatic conditions of Swabi

region.



Regarding plant development and phenology, the application of humic acid with

N did not enhance the emergence duration of maize seedlings. It is because the effect

of humic acid and fertilizer is not so quick and the emergence of seed primarily depends

on the reserved amount of food in it (Azeem et al., 2014). It is in accordance with the

findings of Rodrigues et al. (2017) wherein the application of humic acid showed no

influence on the ESI (emergence speed index) of maize crop. However, Aragão et al.

(2003) has reported an improvement in the duration of emergence and seed vigour of

several crop species due to humic acid application. These differences may be due to the

variations in various factors such as crop developmental stage, type of humic acid and

its mode of application (Rodrigues et al., 2017). These results are in consonance with

those of Moselhy and Zahran (2002) who reported that seed emergence is not affected

by N fertilizer and it is dependent on its own endosperm reserves rather than the external

sources of nutrients (Hafidi et al., 2012). According to Major (1980) it is the genetic

factor and not the nitrogen fertilizer which affect the number of days taken by the maize

seed to emerge.

Furthermore, increase in the amount of humic acid + N significantly reduced

the number of days from planting to 50% tasseling and silking, and ASI (anthesis-

silking interval) in maize genotypes as was observed at 1.8 kg HA ha-1. These findings

are in agreement with findings derived by Ghazal et al. (2013) and El-Mekser et al.

(2014) in which they reported 50% early tasseling and silking in plots, where humic

acid was used. The underlying reason for it may be that humic acid positively

accelerated plant physiology, plant dry matter production, lateral roots initiation, cell

respiration and hormonal activities, and nutrients uptake by plant cells (Puglisi et al.,

2009). Gul et al. (2014) reported significantly earlier 50% tasseling in plots treated with

organic sources of fertilizers due to continuous supply of plant nutrients for a longer

175

period of time. Khan and Parvej (2011) observed significantly earlier silking in maize

when rice straw (organic manure) was used as a source of nutrients as it resulted in

enrichment of soil OM status. The shorter ASI (anthesis to silking interval) was found

under 1.8 kg ha-1 HA application in our trials. This could be the result of attaining early

tasseling and reduced silking of maize plants due to humic acid treatment (Kolari et al.,

2014). In a similar way, increase in N fertilizer resulted in early tasseling, silking with

reduction in ASI (anthesis to silking interval). These results are in line with Sola et al.

(2004) findings in which the nitrogen fertilizer received plots attained 50% tasseling

and 50% silking one week earlier than control plots. Jassal et al. (2017) noted that use

of nitrogen as well as increase in its level induced earliness both in tasseling and silking

of maize crop. It may be attributed to the positive impact of N on these phenological

processes due to its positive impact on C/N ratios of maize plants; and smooth

absorption and utilization of N in meristematic tissues as well as metabolic processes

during photosynthesis (El-Gizawy and Salem, 2010). Dawadi and Sah (2012) are also

of the opinion that increasing N levels reduce the number of days taken by the maize

crop to reach tasseling and silking stages of growth which results in lower ASI duration

(anthesis to silking interval). The shorter ASI with high rate of N application may be

due to inducement of early and rapid growth (Kolari et al., 2014) because maize (Zea

mays L.) is a nitropositive crop (Gökmen et al., 2001). Effa et al. (2012) and Amandeep

et al. (2012) findings also corroborated our results, who recorded early tasseling and

silking by maize crop in response to N application.

The number of days taken by the maize genotypes to attain their physiological

maturity increased linearly with increase in humic acid and N levels and maximum days

were observed at 1.8 kg ha-1 HA + 240 kg N ha-1. Likewise, seed fill duration (SFD)

lengthened with increase in the amount of humic acid and nitrogen. The application of

humic acid at 1.8 kg HA ha-1 resulted in longer SFD. The delayed maturity and longer

seed fill duration may be due to higher available moisture and increased fertility level

(both macro and micro nutrients along with OM) of the soil during crop growth because

of humic acid application (Santa and Shrestha, 2014; Khan and Jan, 2017). As humic

acid is a gradual release fertilizer of N; the plants remained green and succulent for a

longer period of time with increased chlorophyll content (Khan et al., 2014). Dawadi

and Sah (2012) are also of the opinion that the SFD of maize is lengthened with

increasing organic fertilizer level. Similarly, the likely reason for increase in days to

176

maturity and SFD due to N application may be the long photosynthetic period (Oikeh

et al., 1997) that enhanced the leaf durability and delayed these phenological traits in

the crop (Edemeades et al., 1993; Gungula et al., 2003). Late maturity and increase in

SFD may be attributed to maize healthy growth and development as more nutrients

were supplied by fertilized plots (Sharif et al., 2004). The results obtained suggested

that heavy doses of N fertilizer reduced early senesces chances of maize crop and

positively enhanced their photosynthetic activities as well as seed fill duration (SFD)

due to luxurious growth and rich chlorophyll content. These are matching with the

findings of Shrestha (2013) who observed increased physiological maturity and SFD

when higher amount of N fertilizer was applied in comparison to control in maize

genotypes. The treatments that received high doses of nitrogen achieved delayed

physiological maturity and retained longer SFD as compared to control plots during

both the years of the trial. Higher nitrogenous fertilizer enhanced the succulence of

plants and delayed the senescence of leaves as the plants were staying green (Dawadi

and Sah, 2012). Among genotypes, early tasseling, silking and short physiological

maturity of Iqbal variety may be due to its genetic and inherited characteristics. Due to

this reason, Azam et al. (2007) reported different phenological days for various maize

genotypes.


of maize genotypes

The dry matter production (total weight plant-1) of maize genotypes both at

silking and maturity stages, got improved with the application of humic acid + N in our

study. The maximum dry weight was recorded at 1.8 kg HA ha-1 which is in consonance

to the findings of Chen et al. (2004) and Khan et al. (2014). Mengel et al. (2001)

reported that the increase in fresh and dry weight of plants may be attributed to the

positive role of N on plant metabolism, plant meristematic activities and acceleration

of photosynthetic rate, which magnitude in the soil increased due to humic acid

application (Qadoons et al., 2015). Moreover, the plant height of maize genotypes also

enhanced with increasing humic acid level up to 1.8 kg ha-1 and N from 0 to 240 kg ha-

1. It may be due to the more number of sinks produced, membrane uptake of nutrients,

better plant physiology and increased biomass production (El-Mekser et al., 2014).

Moghadham et al. (2013) also reported similar findings by the application of humic

acid to maize crop, the main reason of which may be the improvement in root zone

177

growth. Humic acid has beneficial effects on germination, the length of corn seed

radicle and stem growth which results in taller maize plants with increased ear height

above the ground (Eyheraguibel et al., 2008). Similarly, the maize genotypes exhibited

a continuous and gradual increase in plant height at maturity with each incremental unit

of N (integral constituent of chlorophyll tissues of plant) (Rizwan et al., 2003). The

underlying cause may be that higher N levels provided larger leaf area, resulted in more

photoassimilates and dry matter production (Mandal et al., 1992) that promoted sharply

the vegetative and shoots growth of the genotypes. These findings are in line with those

of Inamullah et al. (2011) who reported that accelerating N level from 0 to 300 kg ha-1

improved plant height in maize. Furthermore, these facts are in accordance with the

results of Haque and Jakhro (1996) who studied that nitrogen fertilizer enhanced

vegetative growth along with plant height. Uhart and Andrade (1995) and Rizwan et al.

(2003) also reported similar results and are of the viewpoint that nitrogen is the primary

yield constituent which resulted in taller maize plants. Our results have also been

supported by Shivay and Singh (2000) who studied an increase in maize plant height in

response to N application, as it enabled the crop to disclose its genetic potential for

more vigorous growth.

The absolute growth rate (AGR) and crop growth rate (CGR) of maize

genotypes increased by the combined application of humic acid and nitrogen levels,

both at silking and maturity stages of crop growth. The maximum AGR and CGR were

observed at 1.8 kg HA ha-1. The increase may be due to the stimulatory effect of humic

acid on nutrients availability and other physiological parameters which resulted in

higher leaf area, crop growth and total dry weight plant-1 (Valadabadi and Farahani,

2010; Azeem et al., 2015). Application of humic acid causes an increase in the plant

dry matter (Delfine et al., 2005) which might have affected the AGR and CGR values

of maize genotypes. Latest literature has revealed that HA may be used as a growth

regulator for controlling hormone levels, enhancing stress tolerance and accelerating

plant growth in various crop species (Nardi et al., 2002). N application of 240 kg ha-1

produced maximum CGR that is in line with the findings of Akram et al. (2010) who

reported maximum CGR at 275 kg ha-1 N as compared with lower levels of N. Similar

response of an increase in CGR of maize plant with the addition of N over control has

also been proved by (Ahmad et al., 1993; Mohsan et al., 1999). Likewise, absolute

growth rate (AGR) which is related to the CGR exhibited a positive relationship to

178

increase in N levels during our experiments, from the start of emergence to silking stage

of maize genotypes, the basic reason of which may be more dry matter production due

to better nutrition (Kolari et al., 2014). It is in line with the findings derived by

Amanullah (2004).



Results showed that increase in humic acid in integration with N enhanced the

number of leaves plant-1 at silking. The maximum number of leaves plant-1 was

achieved at 1.8 kg HA ha-1. It may be due to the reduction in soil moisture losses through

evaporation, the availability of both macro and micro nutrients and the improvement of

soil properties near the root zone (Daur and Bakhashwain, 2013). Similarly, the leaf

weight plant-1 at silkinig enhanced significantly with the application of humic acid +

nitrogen. More dry weight plant-1 was recorded when humic acid was applied at 1.8 kg

HA ha-1. The explained reason is that the use of humic acid increased dry matter of

leaves as a result of sustaining photosynthetic machinery of plants (Sharif et al., 2002;

Turkmen et al., 2004) and provision of macro as well as micro nutrients (Khaled and

Fawy, 2011). Nitrogen, further supplements 1-4% of plants dry matter production

(Haque et al., 2001; Gulser et al., 2010). This is an indication of the fact that with

increase in humic acid, the dry weight of leaf also increases. Humic acid causes an

increase in the chlorophyll content of leaves which serves as a primary raw material for

photosynthesis and promotes the growth and biomass production of crops (Mindari et

al., 2014). Likewise, N application of 240 kg ha-1 enhanced the leaves bearing capacity

of maize plots, which is in corroboration with the results of Onasanya et al. (2009)

where the number of leaves plant-1 increased with N fertilizer as compared to control.

The most valid reason may be that N accelerated the vegetative growth of the crop

(increased the number and length of internodes) due to high rate of photosynthesis, and

improved plant height (Paradkar and Sharma, 1993; Liduke, 2014) which resulted in

more number of leaves plant-1. Similarly, maximum leaf weight plant-1 was recorded

under N application level of 240 kg ha-1 in our study. The possible explanation is that

the nitrogen application accelerated the photosynthetic rate of leaves on account of

higher chlorophyll content which brought an improvement in the dry weight of plant

organs and leaves (Aslam et al., 2011; Kolari et al., 2014). Production of heavy and

larger leaves having more leaf surface area (cm2) due to N application may be the

179

primary cause of increase in dry weight of miaze leaves plant-1 (Valentinuz and

Tollenaar, 2006).

The leaf area (cm2) plant-1 at silking stage of maize genotypes was significantly

affected by the application of humic acid and N levels. More leaf area plant-1 was

observed with humic acid addition of 1.8 kg ha-1. The increased levels of humic acid

might have increased maize growth as a result of better nutrition and thus helped in

expanding the leaf area (Atiyeh et al., 2001) as it led towards higher N concentration in

its aerial parts as well as within the roots (Tan, 2003). Besides, humic acid has a strong

impact on root initiation and root growth of plants which favours higher uptake of

nutrients (Pettit, 2004). Likewise, leaf area plant-1 increased with N application levels

and achieved its maximum size (expansion) under N rate of 240 kg ha-1. This parameter

is of crucial importance in plants life because it serves as an indicator for the calculation

of other growth indices like LAI (leaf area index), SLA (specific leaf area), SLW

(specific leaf weight), LAD (leaf area duration) and NAR (net assimilation rate) as

reported by Fageria et al. (2006). Larger leaf area plant-1 as a consequence of N

application further promotes leaf area index (LAI) as compared to control plots having

no N application (Valentinuz and Tollenaar, 2006). It may be attributed to the fact that

enhanced N levels resulted in more RUE (radiation use efficiency) due to lower

senescence and more green surface of leaves. Leaf area plays an important role in

interception of light and plant productivity (Koester et al., 2013) as the final crop yield

is linearly proportional to the total amount of solar radiations received by the crop

leaves during its growth (Milford et al., 1985). Banerjee et al. (2012) has concluded

form his research work that leaf area and leaf area duration are the main causes of yield

differences in crops. The higher leaf area index is correlated with increased leaf area

duration (Shivamurthy, 2005) which results in long lasting assimilatory surface

(Beadle, 1993). Crosbie (1982) and Davics (1992) are of the view that effective longer

leaf area duration in hybrid maize significantly contribute to its increased yield over

open pollinated varieties (OPVs). Larger leaf size is responsible for nitrogen supply to

plant which then stimulates crop growth and development (Trapani et al., 1999).

Results showed that the LAI at silking stage of maize genotypes improved with

increasing the amount of humic acid + N levels in our trials. Application of humic acid

at the level of 1.8 kg ha-1 provided maximum LAI. The most valid reason for increased

leaf area index may be the enhanced photoassimilation and nutrients availability to

180

maize plants as a result of humic acid application (Figliolia et al., 1994; Khaled and

Fawy, 2011). These results have been augmented by many researchers who found that

HA application increased crop growth and productivity, and helped in more moisture

retention of the soil (Suganya and Sivasamy, 2006; Selim et al., 2009; Buyukkeskin

and Akinci, 2011; Celik et al., 2011; Tahir et al., 2011; Kim et al., 2012). N increase in

the soil due to humic acid (Azeem et al., 2014) resulted in higher leaf growth,

maintenance, and accelerated LAI (Haque et al., 2001). The significant response of HA

treatment on the leaf area index along with other growth parameters has also been

studied in cowpea which is a leguminous crop by Haghigh et al. (2011). Humic acid

being a chelating agent for a number of nutrients due to the presence of hormonal

compounds; overcome the deficiency of nutrients and promoted the growth and

development of crops (Albayrak and Camas, 2005). Similarly, the higher leaf area index

due to N application (240 kg ha-1) is in agreement with the research of Akram et al.

(2010) who achieved maximum LAI in maize with 275 kg N ha-1 in comparison to

control plots. The positive impact of N on LAI of maize is also reported by Kumar and

Singh (2001). The higher LAI may be due to increased leaf area duration and more leaf

production (Jasemi et al., 2013).

The results revealed that SLA and LAR plant-1 were substantially affected by

the application of humic acid and nitrogen levels at silking stage of the maize

genotypes. The SLA and LAR plant-1 decreased with increase in the amount of humic

acid perhaps due to more increase in leaf and plant weight as compared to leaf area.

However, Gholami et al. (2014) had reported no impact of humic acid on SLA and

LAR of maize crop. The SLA represents the interception of light per unit of leaf dry

mass, and is related to NAR (Reich et al., 1997). As the level of humic acid increases

the total dry weight of plants increases too, due to sustainance of photosynthetic tissues

(Turkmen et al., 2004). In a similar way, specific leaf area (SLA) plant-1 showed a

negative response to N application in our experiments which is contradictory to the

findings of Amanullah (2004) who reported an increase of 0.152 cm2 g-1 with one kg

increase in the rate of N. On the other hand, these results are in similarity with those

reported by Correia et al. (2000) who established a negative relation between N rate

and maize SLA. It may be due to the fact that the enhanced level of N induced an

increase in the thickness of leaves. Being a vital component of leaves chlorophyll

content it enahced photosynthesis and resulted in more biomass accumulation (dry

181

matter) in the leaves (Kolari et al., 2014). Likewise, LAR (leaf area ratio) serving as a

measure of photosynthetic tool per unit of plant biomass performed a downward trend

with increase in N level because of improvement in plant dry weight (Correia et al.,

2000). Minimum LAR was calculated at 240 kg ha-1 N against control and other levels

of N. Reduction in SLA means more leaf thickness, more chlorophyll and

photosynthetic tissues in leaves, high rate of photosynthesis, efficient use of solar

radiation and more increase in total dry weight (biomass production) of plants

(Azarpour et al., 2014). That is why lower LAR plant-1 was recorded under higher N

rates.



The application of humic acid in integration with N increased ears plant-1 and

maximum ears plant-1 were recorded at 1.8 kg HA ha-1 + 240 kg N ha-1. It is in

agreement with the findings of Albayrak and Camas (2005) who observed the

significant role of humic acid in increasing yield components of mustard. The possible

reason for it may be the improved availability of nutrients, improvement in source-sink

relationship and better moisture retention capacity of humic acid in the soil (Salman et

al., 2005; Mauromicale et al., 2011; Kim et al., 2012). The number of productive plants

and ears m-2 also increased as a consequence of more ear bearing capacity of maize

genotypes due to integration of HA and N. At 1.8 kg HA ha-1 maximum ears were found

per unit area (m2) which is in line with the findings of Iqbal (2014) who reported

maximum productive tillers in wheat crop, treated with humic acid as compared to

control plots. It may be due to the direct positive effect of humic acid on maize

chlorophyll content, respiration acceleration, growth enzymes activation, increased

penetration in plant cells (membranes) and indirectly through improved biological,

physical and chemical conditions of soil (Rajpar et al., 2011). Similarly, higher rates of

N (240 kg ha-1) produced maximum ears plant-1, which resulted in more productive

plants and ears m-2. The underlying reason for increase in number of ears may be the

provision of N in proper amount at reproductive growth stage of the crop (Shah et al.,

2009) which increased the chlorophyll content of plants, photosynthetic activities and

assimilate production. It finally provided maximum dry matter and fresh biomass

production in plants with higher number of ears plant-1 (Sharifai et al., 2012). These

findings are in line with those of Malaiya et al., (2004) who reported that N in

182

combination with organic sources of fertilizer produces more ears plant-1. Balko and

Tussel (1980) also reported an increase in number of ears/plant after N fertilization due

to more plant biomass (dry matter) production which is translocated to reproductive

organs of the maize plants. Ears m-2 also increased as a consequence of high number of

productive plants per unit area. It is in similarity with the research work of Khan et al.

(2005) and Shah et al. (2009) who reported maximum productive plants per unit area

as result of higher dose of N as compared to control due to better nutrient availability.

It may be due to more synchronization in flowering which enhanced the rate of

fertilization and improved number of productive plants during SFD (Gungula et al.,

2007). The lower number of productive plants under N stress may be associated with

reduced size and number of sinks produced, poor translocation of photoassimilates, low

synchronization of flowering and increased abortion of plants (Dawadi and Sah, 2012).

As indicated in the analysis of data, ear weight plant-1, ear length and girth of

maize genotypes showed a positive and linear response to humic acid + N application

and that is why, 1.8 kg HA ha-1 resulted in maximum ear weight, length and girth

(Ghazal et al., 2013). Shuixiu and Ruizhen (2001) and Moghadam et al. (2015) findings

are also in coincidence to our results. The increase in length and girth of ear may be

due to the timely release and provision of nutrients. The efficacy of humic acid to

sustain nutrients for a longer period of time in the root zone and then release in a gradual

and slow manner due to lengthy residue decomposition process may be the underlying

reason for better crop response to HA amendment (Dev & Bhardwaj, 1995; Sharif et

al., 2003). Humic acid creates an improvement in the physioco-chemical properties of

soil and more biomass production then occurs as a result of acceleration in plant

biochemistry, physiology and productivity (Canellas and Olivares, 2014). As stated

earlier, ear length and girth improved with increase in nitrogen levels from 0 to 240 kg

ha-1. These findings have been augmented by Sharifi and Taghizadeh (2009) who

observed maximum length and girth of ears with nitrogen use of 240 kg ha-1 as

compared to control plots. Similar results have also been reported by Hussaini et al.

(2001) and Turgut (2004). It may be ascribed to more assimilate production due to more

N supply as a result of efficient use of solar radiations during photosynthesis (Diker

and Bausch, 2003; Cirilo et al., 2009), and better vegetative growth of the crop which

positively contributed to the higher yield components of maize (Amandeep et al., 2012).

Similarly, significant effect of nitrogen (240 kg ha-1) was noted on dry matter (weight)

183

of ears plant-1 which may be due to the fact that leaves plant-1, LAI, photosynthesis,

photoassimilate availability enhanced in our study as a consequence of proper N supply

that exaggerated dry matter accumulation of plants (Ulger et al., 1997; Bangarwa et al.,

1998; Sharifai et al., 2008). Chung et al. (2000) studied that by using organic sources

of nutrients in combination with inorganic fertilizer of N the maize crop dry matter

yield enhanced manifold as maize crop is an aggressive utilizer of available plant

nutrients (Ayoola and Makinde, 2009). Our results are also confirmatory to the findings

of Bhatt (2012) and Imran et al. (2015) who found a substantial response of maize crop

to varying N rates due to more nutrients availability and assimilates translocation to

plant organs. A rapid increase in plant height, ear weight and dry matter accumulation

was observed.

The increase of humic acid with increase in N rates from 0 to 240 kg ha-1,

substantially contributed to higher number of rows ear-1, grains row-1 and total grains

ear-1 in maize genotypes. Azeem et al. (2014) and Sarir et al. (2005) findings are also

in similarity to our results where maximum number of grains ear-1 (432.2) was recorded

with application of 3 kg HA ha-1 while lower number of grains (400) was observed with

application of 1.5 kg HA ha-1. The underlying reason for increase in plant growth and

yield components (Nisar and Mir, 1989) may be the positive effect of HA on initiation

of root enzymes, and soil rhizosphere (Fahramand et al., 2014). The improvement in

soil CEC, moisture retention capacity, soil microorganism’s activities and root enzymes

stimulation may be associated with enhancement in plant growth and yield components

(Khattak and Muhammad, 2013). Humic acid attracts micronutrients, by forming a

chelate and then slowly releases them according to the plant demand which is associated

with better growth of the crop (Mackowiak et al., 2001). It finally promoted yield of

the crop as was observed by Khattak and Muhammad (2013) when they added HA to

the soil at the rate of 2 kg ha-1. Likewise, grain rows ear-1, grains row-1 and grains ear-1

enhanced with acceleration in N levels. It is because the enhanced level of N application

increased the chlorophyll content of plants which in turn accelerated the photosynthetic

activities with the production of more assimilates, increased the number of sinks for

more photoassimilates and finally promoted the production capacity of maize crop with

improved yield components (Sharifai et al., 2012). Our results corroborated the findings

of Prodhan (1999), Mkhabela and Shikhulu (2011), Younas et al. (2002), Alam et al.

(2003) as well as Sharifi and Taghizadeh (2009) who studied the considerable impact

184

of nitrogen on maize yield components. Bakht et al. (2007) holds the view that higher

amount of N may be useful in improving various vegetative, phenological and

reproductive phases of maize crop. That’s why, Tahir et al. (2008) proved that the

number of grains ear-1 is a genetically controlled factor but environmental and

nutritional level may also positively contribute to this parameter. Akhtar (2001) and

Arif et al. (2010) had also reported a linear relationship among the yield components

of maize and N fertilizer. Efficient utilization of solar radiations, greater assimilates

production and their conversion to starches might have resulted in higher grains ear-1

and weight plant-1 that produced heavier biomass as well as seed yield (Derby et al.,

2004).

Thousand (1000) grain weight is an important physiological parameter in maize

crop and the primary determinat of final grain weight. Therefore, application of humic

acid with increasing levels of N, improved 1000 grain weight of maize genotypes.

Better 1000 grain weight was recorded at 1.8 kg HA ha-1. The rationale for the increase

may be the timely provision of nutrients, resulting in synthesis of more assimilates and

at the same time provision of water to carry assimilates to the sink. The higher leaf area

(cm2) to acquire and capture more solar radiations in response to nutrients better supply

(Khaled and Fawy, 2011; Sharifi, 2017) might has aided in the formation of healthy

and large seed with higher seed weight. Likewise, Moghadam et al. (2015) and

Kuşvuran et al. (2011) have reported the beneficial effect of humic acid in increasing

thousand grain weight of maize. Daur and Bakhashwain (2013) also observed

significant difference for 1000 grain weight across the humic acid levels, wherein it

enhanced in a linear fashion with increase in the humic acid levels. The increased 1000

grain weight of maize genotypes may be associated with more dry matter accumulation

and heavier grains due to timely translocation of assimilates by humic acid utilization

(Delfine et al., 2005) as well as continuous release of nutrients during the crop growth

cycle due to slow organic matter decomposition process (Dev and Bhardwaj, 1995).

Thousand (1000) grain weight of maize genotypes increased radically with N fertilizer

and maximum quantity was recorded at 240 kg ha-1. An increase of 14.1% in grain

weight was observed during the first year of the trial while in the second year an

improvement of 12.3% was measured over control plots of N. The possible reason

might be that higher N doses promoted vigorous vegetative growth of the plants with

the preparation of more photosynthates, which then transported to grain during grain

185

fill duration and resulted in heavier grains formation (Ali et al., 2015). In a similar

pattern, Khan et al. (2011) got best 1000 grain weight with 300 kg ha-1 N application

when compared to control. The increase in grain weight due to different N doses may

be attributed to variation in nutrition. Moreover, comparable results are recorded by

(Khan et al., 1999; Waqas, 2002; Sharar et al., 2003; Akmal et al., 2010). They reported

a marked increase in the size of maize grains when they supplemented crop growth with

heavy doses of nitrogen fertilizer in comparison to lower rates. It was further augmented

by Abouziena et al. (2007) and Akmal et al. (2010) who concluded that by increasing

the N level, 1000 grain weight is enhanced.

The grain yield of maize genotypes enhanced with the use of humic acid in

integration with increasing levels of N (0 to 240 kg ha-1). The data revealed that 1.8 kg

HA ha-1 increased grain yield by 12.62% over no HA (control) plots due to more

transition of nutrients from maize vegetative parts to reproductive organs. Sharif et al.

(2003) had reported an increase of 21-25% in economic yield of maize due to humic

acid application. The possible reason for improved economic yield in association to

humic acid incorporation may be the slow release of nutrients for a prolong period of

time (Dev and Bhardwaj, 1995) and longer photosynthetic activity of crop due to high

chlorophyll content of green leaves (Turkmen et al., 2004). Celik et al. (2010) explained

that incorporation of humus in soil proves beneficial in respect of nutrient uptake,

availability to roots and then transportation to upper parts which results in enhanced

growth, development and yield of maize crop. Bakry et al. (2009) and Yadav et al.

(2011) also observed an increase in the grain yield of maize by the application of humic

acid as it results in increased vegetative growth, photosynthesis and leaf area index

(Ghorbani et al., 2010). In the same pattern, 240 kg N ha-1 provided higher grain yield

of maize genotypes. The underlying reason for improved grain yield may the greater

number of ears plant-1, increased ear length, ear diameter, more grains ear-1, increase in

1000 grain weight and increase in biomass of individual ears as a result of more

assimilates produced by the crop due to better photosynthesis (Khan et al., 2011). It is

in conformity with the findings of Jan et al. (2007) who observed maximum grain yield

when the nitrogen level increased from 180 to 300 kg ha-1. The findings of Sanjeev and

Bangarwa (1997), Zeidan et al. (2006) and Lawrence et al. (2008) are also in agreement

to our conclusions. It is because N is a major plant nutrient and yield deciding factor

for maize crop production (Manzoor et al., 2006) which enhanced nutrients uptake by

186

the crop as well as promoted translocation of photosynthates from source to sink as

reported by Jena et al. (2015) where N application of 240 kg ha-1 resulted in better grain

yield. Our results are further augmented by Dilip and Nepalia (2009) who obtained

maximum grain yield of maize due to the efficient crop growth rate and improvement

in yield parameters like plant height, LAI, biomass (dry matter) production, cob length

and girth, number of grains cob-1 and test weight etc. as a result of higher level of N

fertilization.

Biological yield (BY) of maize genotypes also got improved with the treatment

of humic acid in integration with increasing N levels (0 to 240 kg ha-1) in our trials.

Therefore, 1.8 kg HA ha-1 brought an improvement of 8.63% in BY as compared to

control plots. This positive response may be related with water supply in sufficient

amount, reduced evaporation from soil surface due to higher moisture holding capacity

and efficient growth rate etc. in maize plants (Azarpour et al., 2011). Rezvantalab et al.

(1998) reported that application of humic acid increased nitrogen and phosphorus use

efficiency, accelerated dry matter production and resulted in the increased biological

yield. Ayas and Gulser (2005) also proved the beneficial effect of HA on increased

plant height, growth, and biological yield by raising the nitrogen content of the plant.

Similarly, the gain in biological yield of maize genotypes over control due to N levels

may be ascribed to the effective N uptake by the maize plants and its synergistic effects

on plant growth (Khan et al., 2011). It may also be associated with excellent CGR, LAI,

LAD, lengthy life cycle and seed fill duration which resulted in maximum utilization

of the available solar radiations and provided higher biological yield (Hammad et al.,

2011). Our results confirmed those of Cheema et al. (2010) who reported that nitrogen

convincingly improved maize yield, when applied in combination with organic manure.

It is also augmented by Deksissa et al. (2008). Optimum use of solar light, synthesis of

assimilates in greater amount and their conversion to carbohydrates resulted in more

grain production and weight that produced more biomass of the maize plants (Derby et

al., 2004). Likewise, stalk yield enhanced with increasing N levels and highest stalk

yield was recorded with 240 kg N ha-1. The possible reason for increase in stalk yield

may be the conducive environment for root growth, increased vegetative growth, plant

height and biological yield as a result of N treatment (Jan et al., 2007; Cheema et al.,

2010). The lowest stalk yield was observed in those plots where no N was applied

(Xiang et al., 2001).

187

Harvest index (HI) which is an indicator of the plants ability to convert

photoassimilates into grain yield, showed a substantial response to humic acid + N

levels on maize genotypes in our study. The higher HI was recorded with 1.8 kg HA

ha-1. Our results are consistent with the findings of Rezazadeh et al. (2012) who noted

a positive correlation between humic acid and harvest index of maize crop.

Improvement in phsico-chemical and microbial activities of soil, moisture holding

capacity, CEC and enzyme nitrogenase activity (Sharif, 2002; Khattak and Muhammad,

2013) caused optimum utilization of solar light and greater assimilates production.

Assimilates were then converted to starches which produced heavier grains ear-1 with

healthy plants and finally resulted in more biomass production and yield components

of maize (Derby et al., 2004). In a similar way, maximum HI was noted when N

fertilizer was used at the higest rate of 240 kg ha-1. It is because N application caused

significant changes in total dry matter production, LAD, LAI and CGR which finally

affected harvest index of the maize crop (Hammad et al., 2011). With an efficient

supply of N in the soil, the plants chlorophyll content got improved, which resulted in

stay green leaves of the plants. Moreover, the plants overcome nutritional deficiency to

supply N and photoassimilates to its seeds for a lengthy period of time and ultimately

produced higher harvest index as a consequence of more grain yield (Eghball and

Power, 1999). These findings are in coincidence to the conclusions of Khan et al. (2011)

who found that HI of maize influenced markedly by enhancing N level ha-1 as a result

of increased grain yield. It also corroborated the findings of Cheema et al. (2010) who

found maximum harvest index under higher N level as compared to control plots having

no organic or inorganic fertilizer. It is an indication of the fact that when N fertilizer is

properly managed it improves yield and HI of maize genotypes in comparison to control

treatments. The observations of Sabir et al. (2000) are also in support of our results.

The nitrogen use efficiency (NUE) of maize genotypes which is in other words

the uptake of nitrogen from root zone by the plants and conversion into plant dry matter,

enhanced with increase in humic acid when it was used in integration with different

rates of N, as noted at 1.8 kg HA ha-1 in our trials. The correlated reason may be that

HA is the combination of both macro and micro nutrients in the form of chelates whose

application results in enhanced nutrients availability as well as their uptake (Madronová

et al., 2001; Tan, 2003). The organic matter of humic acid acts as a store house of N,

P, K, S, Ca, Mg and Zn etc. (Jayaganesh and Senthurpandian, 2010) and prevents

188

leaching of N in the form of NO3 (Swift et al, 2001) which accelerated the uptake of

nitrogen and its use efficiency. The deeper root length and acceleration of cell

membrane permeability as a consequence of humic acid amendment (Tahir et al., 2011;

Azeem et al., 2014) may also be counted for improved NUE. Similar results have also

been derived by Chen and Aviad (1990), and Khaled and Fawy (2011) as according to

them HA have positive impact on the growth of different types of soil microorganisms

which stimulate N uptake, the macro plant nutrient. They recorded maximum N uptake

under 2 g humus kg-1 treatment. It means by stimulating N uptake humic acids can also

help in reducing N leaching and minimizing ground water pollution (Schofield et al.,

2012). Eyheraguibel et al. (2008) stated that root growth of maize is enhanced by humic

acid application which results in increased nutrients uptake in the soil, especially N as

it is highly mobile in the form of NO3- (Zhong et al., 2014). The reports showed that

agronomic-nitrogen use efficiency (NUE-AE) and partial factor productivity-nitrogen

use efficiency (NUE-PFP) of maize genotypes declined with increase in the amount of

nitrogen fertilizer beyond 180 kg ha-1 and 120 kg ha-1 respectively. Lower NUE-AE

and NUE-PFP were observed under N amendment of 240 kg ha-1. It is in agreement

with the findings of Pikul et al. (2005). They observed an inverse relationship between

increased N application rates and N use efficiency because its efficiency is reduced by

increasing N rate beyond a certain point. The primary reason may be that heavier doses

of N could cause more losses of nutrients relatively (Niaz et al., 2015). Secondly, with

the increasing N supply the crop genetic potential has been achieved and furthermore,

little improvement in the grain yield is possible because the crop has many other yield

limiting factors (determinants) besides nitrogen too (Dobermann, 2007). According to

the findings of Almas (2009) synchronization in N demand and supply is must for

improving yield and NUE through split applications of fertilizers at various stages of

maize crop during its life cycle.

The net assimilation rate (30-75 DAS) of maize genotypes got improved by the

use of humic acid (1.8 kg HA ha-1) in combination with increasing rates of N, which is

matching with the results of Azeem et al. (2015) who used HA at the rate of 1.5 kg ha-

1 in his experiments. Motaghi and Nejad (2014) also reported the promotive effect of

humic acid on NAR as it is responsible for increased root length and nutrients

availability, which in turn makes better use of the available nutrients (Pettit, 2004). It

seems that the photosynthetic machinery got stimulated with these nutrients which

189

created new sinks for them and NAR was accelerated. Likewise, net assimilation rate

(30-75 DAS) exhibited significant response to N fertilizer in our trials, which is in

accordance with the findings of Moussa and Bersoum (1995) and Mohsan (1999).

Faheed et al. (2016) also observed similar results, where the application of N increased

NAR in an efficient way. It may be due to the beneficial effect of N on maize as it is a

nitropositive crop (Gökmen et al., 2001) and responds well to N application under

favourable soil moisture conditions (Saleem, 2010). The higher nutrients concentration

in the root zone of the plants provided higher LAI that probably captured more solar

radiations, accelerated the rate of photosynthesis, decreased plants respiratory losses

and finally resulted in higher NAR (Habib et al., 2016).

The grain protein content (%) of maize genotypes improved with increasing the

amount of humic acid + N levels; and maximum grain protein content (%) was reported

with humic acid used at the rate of 1.8 kg ha-1. These results are in consonance with the

observations of Delfine et al. (2005) and Morard et al. (2011). The increase may be due

to the positive effect of humic acid on various biochemical processes (photosynthesis,

respiration, hormonal activities and enhanced protein synthesis) in the cell wall,

cytoplasm and cell membrane of maize plants (Chen et al., 1999). Application of HA

led to the increased production of nitrogen in aerial parts (reproductive organs) as a

result of growth induction in shoots and under ground portion (roots) of maize crop

(Tan, 2003). In the same fashion, increasing levels of N fertilizer significantly

influenced the seed protein content (%) of maize genotypes in our trials. The highest

protein content was exhibited in those seeds which were treated with N dose of 240 kg

ha-1. It reveals that N is a primary constituent of protein and amino acids which

contributed considerably to the increase of protein content in maize seeds. It is in

agreement to the findings of Rafiq et al. (2010) who reported an improvement in the

seed protein (%) of maize crop with each additional unit of N fertilizer applied. It further

confirmed Khan et al. (2011) findings who recorded maximum maize seed protein

content with the addition of 300 kg N ha-1 in comparison to 75 kg N ha-1. The results of

Asif et al. (2013) are also supporting our findings.


The organic matter being an essential and crucial component of the soil and crop

production system, improved with increase in humic acid and N levels and maximum

OM was observed at 1.8 kg HA ha-1 in our study which is in agreement with the findings

190

of Azarpour et al. (2011). It may be as a consequence of the positive effect of HA on

physico-chemical properties of soil such as soil fertility, water holding capacity, soil

organic carbon and CEC i.e. cation exchange capacity (Hanafi and Salwa, 1998;

Khattak and Muhammad, 2013) because it is an organic acid which accelerates the

process of decomposition (Tahir et al., 2011). As reported by Kumar et al. (2007)

application of nutrients in combination with HA materials can boost up crop yield as it

helps in maintaining soil structure and stability. Khaled and Fawy (2011) are of the

view point that humic acid is a useful compound and it can be used for improving soil

bio-chemical properties, increasing nutrient availability and organic matter status

because it makes up 65 to 70% of the organic matter (Nelson and Sommers, 1996;

Baldock and Nelson, 2000; Pettit, 2004; Esmaeilzadeh and Ahangar, 2014). OM

enriched soil further enhances crop growth rate and quality as a result of soil moisture

retention and its temperature control (Hamayun et al., 2011; Zribi et al., 2011).

Similarly, N application of 240 kg ha-1 enhanced the organic matter content (%) of the

soil (0-20 cm) at maize harvest in comparison to control treatments because it

constitutes an important fraction (0.032%) of the OM (Khan et al., 2014). It is in

agreement with the findings of Iqbal et al. (2012) who observed maximum SOC (soil

organic content) with 160 kg N ha-1.

The N content of soil (%) at maize harvest also got enriched with HA + N

application rates as shown in our study. Maximum soil N content was recorded at 1.8

kg ha-1 HA application because it acts as a pool for nutrients supply (Frank and Roeth,

1996) and is a slow release fertilizer of nutrients, especially N (Khan et al., 2014). It is

in line with Masciandaro et al. (2002) who reported that HA can counteract the

unfavourable climatic and edaphic conditions of soil (temperature, pH and salinity) and

can increase the availability of nitrogen in the soil. The inhibitory effect of humic acid

on urease enzyme activity can lead to reduce N losses and hence accelerate N

concentration of the soil (Vaughan and Ord, 1991). Likewise, the N content (%) of the

soil at maize harvest got enriched with higher rates of nitrogen application (240 kg ha-

1) in comparison to 0 kg N ha-1 (control) in our study. The reason for improvement in

N% may be associated with the enhanced OM of the soil as a consequence of N

application because N is an integral component of organic matter (0.032%) (Khan et

al., 2014). The findings of Iqbal et al. (2014) are also in support of our results.

The P content of the soil (mg kg-1) exhibited an improvement as a result of

191

humic acid application (1.8 kg HA ha-1) + N levels in our trials. The underlying reason

may be that humic acid stimulates the microbial activities in the soil which results in

increased P content of the soil (Mayhew, 2004). It is also supported by the findings of

Tahir et al. (2011). Humic acid has the potential to solubilize insoluble P by reducing

P fixation and thereby improve P concentration in the soil (Sibanda and Young, 1986;

Hua et al., 2008). In a similar way, phosphorous (P) content of the soil (mg kg-1) at

maize harvest showed a synergistic and positive relationship with successive

incremental doses of N fertilizer in our experiments. Maximum soil P was observed in

plots treated with 240 kg N ha-1 perhaps due to the synergistic impact of N on soil P

(Malvi, 2011) because NH4+ ions are supposed to have stimulatory effect on enzyme

phosphatase activity (Squires, 2013). It is thought that N have structurally abundant of

phosphatase enzymes and if sufficient N is available in the soil it may enhance the

phosphatase activity, mineralization of organic P and consequently the availability of

inorganic P in the soil (Wang et al., 2007).


More net income (NI) was produced with 1.8 kg HA ha-1 when it was used in

integration with N levels, due to more yield under higher rate of humic acid application

(Niaz et al., 2016). Likewise, a value cost ratio (VCR) of 4.87 was obtained under 1.8

kg HA ha-1 application which represents more than 100% profit of the expenditure

incurred on humic acid (Dilshad et al., 2011). It is regarded as the net return of money

invested on crop production and depends on the cost of fertilizer. When VCR value is

2 it indicates more than 100% return of the cost incurred on fertilizer. A VCR lesser

than 2 represents that margin return of farmer’s becomes uneconomical and risk exists

for investing his money in the crop production either due to poor management practices

or bad weather conditions. However, it is not always useful as it does not take in to

account the residual effect of previous fertilizers applied to the preceding crop and

higher VCR usually occurs at the lower end of the cost of fertilizer (Dilshad et al.,

2010). Furthermore, maximum net income was achieved under higher rates of N

application (240 kg N ha-1) due to the promotive effect of N on maize yield (Nepalia et

al., 2009.) Finally, a higher VCR (value cost ratio) of 5.87 was obtained at 240 kg N

ha1, which represents more than 100% profit on the amount of money spent on N

fertilizer (Dilshad et al., 2011).

192

5.7 Genotypes×humic acid×nitrogen levels

The interaction of N×HA revealed that the grain protein (%) of maize genotypes

got enriched with the application of humic acid and N fertilizer. Similar results were

derived for N×G, HA×G and G×HA×N interactions. It may be attributed to the higher

water uptake by plants and better mineral nutrition as a consequence of their combined

application (Delfine et al., 2005; Morard et al., 2011). Iqbal variety of maize showed

higher grain protein content due to the different qualitative characteristics of maize

genotypes (Olakajo and Iken, 2001). HA×G interaction demonstrated that humic acid

improved the amount of organic matter in the soil. N×HA interaction also followed the

same trend. It may be due to the significant influence of humic acid on soil properties,

mineral nutrition and N availability as it constitutes 5% fraction of humic acid (Khan

et al., 2014). Similarly, the interaction of N×HA indicated that the phosphorous

quantity of soil enhanced with the application of humic acid as they have synergistic

and positive impact on the availability of other nutrients. It is supported by Wang et al.

(1995) who observed that absorption of P improved by 25% in the soil when humic

acid was applied as it is a mixture of plant nutrients (Aiken et al., 1985). The interaction

N×HA, N×G, HA×G and G×HA×N confirmed that the nitrogen use efficiency (NUE-

AE and NUE-PFP), N content of the soil and its uptake by the maize genotypes

enhanced with the combined application of humic acid and N levels (Dilshad et al.,

2010). The underlying reason is the improvement in physic-chemical properties of soil

and increase in microbial activities (Sánchez-Monedero et al., 2004; Liu et al., 2009).

The hybrid 55w65 exhibited higher nitrogen use efficiency as a consequence of

different genetic make up (Olakajo and Iken, 2001).

The interaction of N×HA showed that days to 50% tasseling, silking and ASI

interval decreased with increase in N nutrient and humic acid levels. N×G also

exhibited the same response on maize genotypes for days to 50% tasseling and silking.

It may be ascribed to the availability and uptake of nutrients in sufficient amount due

to organic and inorganic sources of nutrients which enhanced plant growth (Celik et al.,

2010). The interaction of N×HA confirmed that seed fill duration and physiological

maturity of maize crop become lengthy under higher doses of nutrients. The interactions

of N×G and HA×G also demonstrated the marked influence of nitrogen and humic acid

on SFD and maturity of maize genotypes. It may be due to the fact that these nutrients

accelerated the vegetative growth of the crop which ultimately delayed maturity and

193

lengthened the seed fill duration (Saleem et al., 2006). The genotypes used performed

differently regarding the initiation of their phenological stages which is due to their

genetic make up (Ahmad et al., 2000).

The interaction of N×HA indicated that the number of leaves plant-1, plant

height as well as ear height of maize crop enhanced with the successive applications of

nitrogen and humic acid fertilizers. The N×G interaction also followed the same trend

for maize genotypes. The underlying reason may be that plenty availability of nutrients

accelerated the vegetative growth of the crop which resulted in taller plants with higher

number of leaves plant-1 (Yadaw et al., 1990). The hybrid 55w65 produced more leaves

and taller plants as compared to other cultivars of maize. It may be attributed to the

genetic make up of maize genotypes (Faisal et al., 2015). The interaction of N×HA

proved that leaf area and leaf area index (LAI) of maize genotypes improved with the

incremental doses of nitrogen and humic acid. The same response was noted for N×G,

HA×G and G×HA×N interactions. It may be due to the fact that humic acid which is

an organic fertilizer improved the physical condition of the soil, moisture retention,

mineral nutrition and uptake of N nutrient (Tahir et al., 2011: Zribi et al., 2011: Daur

and Bakhashwain, 2013) which resulted in higher leaf growth of the crop (Akmal et al.,

2010). However, the hybrid 55w65 recorded maximum leaf area as well LAI due to

varying genetic potential of maize genotypes (Utobo et al., 2010). The interaction of

N×G evaluated the stimulatory effect of N nutrient on leaf weight and ear weight plant-

1 of maize at silking stage. It is because of the fact nitrogen is an essential component

of chlorophyll (Amujoyegbe et al., 2007) and results in luxurious vegetative growth

(Madani et al., 2012). The interactions of N×G and HA×G showed the substantial

response of N fertilizer and humic acid on total weight plant-1 of maize at silking. It

may be attributed to the fact that the combination of organic and inorganic nutrients

improved organic matter status of the soil and resulted in healthy taller plants (Iqbal et

al., 2012). The N×HA interaction resulted in more ear weight and total weight plant-1

at the maturity stage of crop. The interactions N×G, HA×G and G×HA×N also resulted

in more weight plant-1 in maize genotypes. The slow release of nutrients for longer

duration of time due to humic acid application (Dev and Bhardwaj, 1995) and better N

availability (Khan et al., 2005) might be the underlying cause for increase in dry matter

of maize plants and ears.

194

The interaction HA×G revealed that specific leaf area plant-1 (SLAP) and leaf

area ratio plant-1 (LARP) decreased with humic acid application. The similar trend was

observed for N×G which reveals negative impact of N nutrient on the above parameters.

It may be due to the improvement in physic-chemical properties of soil, organic matter,

P2O5 concentration, N content that accelerated the rate of photosynthesis, metabolic

processes inside plant cells, enhanced plant growth and finally dry mass of leaves

(Nofal et al., 2005; Hati et al., 2007). Lower SLA and LAR were reported in maize

hybrid 55w65 in comparison to other maize genotypes because of thicker leaves. The

N×HA showed the considerable impact of humic acid and nitrogen on AGR and CGR

of maize genotypes at silking. Same response was also observed for N×G and HA×G

interactions. Likewise, the significant influence of N×HA and N×G was recorded on

AGR, CGR of maize genotypes at maturity and NAR (30-75 DAS). It may be due to

the increase in organic matter, microbial activities and nutrients availability of soil to

meet the crop growth requirements because of organic fertilizer (humic acid) and N

application (Edwards and Someshwar, 2000; Mohamed et al., 2006). Higher values of

AGR, CGR were observed for maize hybrid 55w65 due to thicker leaves as it results in

accelerated yielding potential of maize genotypes (Fageria et al., 2006) due to rich

chlorophyll content and higher photosynthetic capacities (Craufurd et al., 1999). The

NAR (30-75DAS) was higher for OPV Iqbal against other maize genotypes because of

varying response of these to soil fertility level and changing environmental conditions

(Ahmad, et al., 2000) due to their genotypic variation (Qamar, et al., 2007).

The interaction of N×HA showed the positive impact of nitrogen and humic

acid on number of ears plant-1 and per unit area. The N×G indicated the stimulatory

effect of N nutrient on ear bearing potential of maize genotypes. It may be due to the

abundant N supply and improvement in soil structure as a result of humic acid

application (Malaiya et al., 2004). The hybrid 55w65 provided more ears plant-1 which

reveals varying yield potential of maize genotypes (Shah et al., 2009). The N×HA

interaction exhibited that grains ear-1, 1000 grain weight, grain yield, biological yield

and harvest index of maize genotypes got improved with the combine use of humic acid

and N levels due to their synergistic effect (Niaz et al., 2016). The same effect was

noted in case of N×G, HA×G and G×HA×N interaction on maize cultivars. It may be

attributed to the long decomposition process of residue, slow release of nutrients

(Sibanda and Young, 1989; Dev and Bhardwaj, 1995), provision of nutrients (macro

195

and micro) in sufficient quantity (Sarir et al., 2005; Azeem et al., 2014), increase in

water retention capacity of the soil (Shah et al., 2009) and sustaining of photosynthetic

tissues of the plants due to humic acid amendment (Turkmen et al., 2004). Humic acid

has the specific potential to control the availability of N in the soil due to its adsorption

capacities for ammonical form (NH3) of N (Mackowiak et al., 2001). It is in agreement

with the findings of Sharif et al. (2003) who reported up to 25% increase in the grain

yield of maize as a result of humic acid application along with other nutrients

accumulation in the soil. It is also supported by Ortiz-Monasterio et al. (1997) who

explains that N nutrient accelerates grain and biomass yield of maize crop. Similarly,

Akhtar et al. (2001) and Arif et al. (2010) reported maximum yield components of

maize crop in response to N application due to optimum use of solar radiations, greater

assimilates production and starch formation. In our trials, better yield and yield related

traits were reported for maize hybrid 55w65 against other genotypes which is an

indication of their differential yield response to various cultural and nutrient

management practices (Ali et al., 2011).

196

6. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

Agriculture is considered as the backbone of our national economy and is

mainly dependent on the balanced use of natural resources like land, soil, water and

nutrients available within the soil horizon. The need to escalate agricultural productivity

in Pakistan which is suffering from food shortage is obviously clear. Growing more

food for meeting the requirements of its growing population is the demand and cry of

the day. Climate change and at the same time rapid degradation of our ecosystem

impose new limitations on crop production. Thus for preservation of natural resources,

sustainable agriculture has to play an important role. The promotion of agricultural

productivity per unit of land area, lowering of production cost, maintenance of soil

fertility along with quality produce is the upmost challenge for the agricultural scientists

of the country. Since the era of green revolution the use of synthetic fertilizers has

become indispensable; largely as a consequence of positive response of crops to it.

Although crops yield is improved but it has caused numerous environmental issues and

hazards such as soil degradation, water pollution, and low return of fertilizers used. To

surmount these issues and difficulties, amalgamated nutrient management and high

yielding genotypes are considered the only possible way for improving grain yield and

enriching soil fertility as well as nutritional status. The current trials were therefore,

planned to estimate the efficiency of highly productive maize genotypes and soil

productivity level under the combined effect of easily available nutrient of nitrogen

fertilizer and gradually released organic source of humic acid. The experiments were

conducted in the Agricultural Research Station Swabi, KPK, Pakistan during 2014 and

2015. The experimental location is distinguished by high temperature (summer), lower

organic matter of the soil (< 1%) as well as alkaline pH. The trials composed on three

treatment levels (genotypes, humic acid and nitrogen). Four genotypes (3025, 55w65,

Jalal and Iqbal), four levels of humic acid (HA) (0, 0.6, 1.2 and 1.8 kg ha-1) and four

nitrogen (N) doses (0, 120, 180 and 240 kg ha-1) were used in the experiment which

also have a control level (no application of HA and N).

Findings of the studies revealed that genotypes, humic acid and N fertilization

significantly affected all growth parameters of maize (days to taseling, silking and

maturity) and yield as well as quality of the crop. Genotypes, HA and N positively

influenced days to 50% tasseling and silking of maize. More days to tasseling, silking

and maturity were counted for 55w65 genotype, followed by 3025 which was at par

197

Jalal variety; while OPV Iqbal resulted in lower number of days to tasseling, silking

and maturity. Regarding humic acid, more days to tasseling and silking were counted

in plots not treated with humic acid. When HA application rate increased, days to

tasseling and silking were decreased. Humic acid application of 1.8 kg ha-1 resulted in

early tasseling and silking, while the maturity of crop got delayed with the increase in

humic acid. 240 kg N ha-1 induced early tasseling and silking while control plots

resulted in late tasseling and silking and early physiological maturity. Physiological

maturity of crop delayed with increasing rate of nitrogen fertilizer. Genotype 55w65 at

1.8 kg humic acid ha-1 took more days to seed fill duration (SFD), followed by 3025

while Iqbal variety took less time in SFD (25.81). Moreover, application of N at the

level of 260 kg ha-1 provided more SFD while plots without N provided less SFD.

More leaves and leaf weight plant-1 was recorded in the plots treated with

genotype 55w65 which was at par with Jalal, while Iqbal variety resulted in lower

number of leaves and leaf weight plant-1. All the levels of N used in the experiments

resulted in more number of leaves and leaf weight plant-1 than control plots. Nitrogen

application at the rate of 240 kg ha-1 provided more leaves plant-1 while control plots

resulted in lower no of leaves plant-1. Likewise, higher leaf area index (LAI) was

measured in plots sown with hybrid 55w65 while Iqbal variety resulted in lower LAI.

Humic acid application at the rate of 1.8 kg ha-1 produced maximum LAI, followed by

1.2 kg HA ha-1 while 0 kg HA ha-1 resulted in lower LAI due to reduced leaf area

surface. Nitrogen treatment (240 kg ha-1) produced more LAI as compared to other

levels of N. The highest specific leaf area (SLA) plant-1 was observed in plots sown

with Iqbal variety while hybrid 55w65 produced lower SLA per plant. Moreover, HA

application at the rate of 1.8 kg ha-1 produced lowest SLA plant-1 while no HA treated

plots resulted in higher SLA per plant. SLA plant-1 was higher in control plots of N,

followed by N application at the rate of 120 kg ha-1 while 240 kg ha-1 N resulted in

lower SLA plant-1. Similarly, leaf area ratio (LAR) calculated was higher for Iqbal

variety, followed by OPV Jalal while hybrid 55w65 resulted in lower LAR due to more

leaf thickness. Higher dose of humic acid application (1.8 kg ha-1) provided lower LAR

while control plots of humic acid produced higher LAR. Higher dose of N application

produced lower LAR as compared to control plots of N (0 kg N ha-1).

Regarding maize genotypes, 55w65 and 3025 produced higher AGR (absolute

growth rate) and CGR (crop growth rate) at silking and maturity stages respectively

198

while OPVs Jalal and Iqbal were lower in AGR and CGR. Humic acid application

increased AGR and CGR in a linear fashion. Moreover, AGR and CGR were higher in

plots supplemented with 240 kg ha-1 N while control plots provided lower AGR and

CGR. More ear weight and total weight plant-1 of maize was recorded for 55w65

genotype while OPV Iqbal resulted in lower ear weight and total weight plant-1 of

maize. Among HA levels, ear weight and total weight plant-1 were higher in plots

treated with 1.8 kg HA ha-1 as compared to control plots of humic acid. Moreover, N

application increased ear weight and total weight plant-1 of maize as its application rate

increased from 0 to 240 kg ha-1. Furthermore, taller plants with higher ear hieght were

recorded for genotype 55w65, followed by 3025 and Jalal while OPV Iqbal produced

plants of short stature with lower ear height. Likewise, humic acid application at the

rate of 1.8 kg ha-1 produced taller plants with larger ear height, followed by 1.2 kg ha-1

HA while plots without humic acid resulted in dwarf plants of lower ear height.

Similarly, 240 kg N ha-1 produced taller maize plants with higher ear height in

comparison to other levels of N.

More ears plant-1 were recorded for genotype 55w65, followed by 3025 while

Iqbal genotype resulted in lower number of ears plant-1. Regarding humic acid

application, higher ears plant-1 were observed in plots supplied with 1.8 kg ha-1 HA,

followed by 1.2 kg ha-1 HA while plots of 0 kg ha-1 HA resulted in lower number of

ears plant-1. While considering N fertilizer, the number of ears plant-1 enhanced as the

rate of nitrogen application increased from 0 to 240 kg ha-1. Similarly, more grains ear-

1 were calculated for genotype 55w65, followed by 3025 while Iqbal variety resulted in

fewer grains ear-1. Moreover, humic acid application at the rate of 1.8 kg ha-1 resulted

in higher grains ear-1, followed by 1.2 kg HA ha-1 while lower grains ear-1 were recorded

in control plots of humic acid (0 kg HA ha-1). Similarly, N application at the level of

240 kg ha-1 produced higher grains ear-1 while lower grains ear-1 were counted in

control plots of N fertilizer. Furthermore, ear length and girth was higher in samples of

55w65. Likewise, 240 kg N ha-1 resulted in higher ear length and girth, followed 180

kg ha-1 N while control plots of N (0 kg N ha-1) produced lower ear girth and length.

Additionally, 1000 grain weight which is considered an important grain yield

contributing factor was higher in samples collected from 55w65, followed by 3025

while it was lower in OPV Jalal. Among humic acid levels, 1.8 kg ha-1 HA produced

higher 1000 grain weight, followed by 1.2 kg ha-1 HA while control plots of humic acid

199

resulted in poor 1000 grain weight. While considering N levels, higher 1000 grain

weight was observed in plots treated with 240 kg ha-1 N, followed by 180 kg ha-1 N

while 0 kg ha-1 N produced grains of lower 1000 grain weight.

Higher biological and grain yield was reported in plots sown with genotype

55w65, followed by 3025 while Iqbal genotype produced lower biological and grain

yield. Regarding humic acid, HA application at the rate of 1.8 kg ha-1 provided higher

biological and grain yield of maize genotpes, followed by 1.2 kg ha-1 humic acid while

control plots of humic acid resulted in lower biological and grain yield. In a similar

fashion, 240 kg N ha-1 produced higher biological and grain yield as compared to 0 kg

N ha-1. Moreover, higher harvest index (HI) was recorded in plots treated with maize

genotype 55w65, followed by 3025 while Jalal variety resulted in lower harvest index.

Similarly, it was observed that the application of humic acid linearly enhanced the

harvest index of maize crop. The application of humic acid at the rate of 1.8 kg ha-1

produced higher harvest index, followed by 1.2 kg ha-1 humic acid while control plots

of humic acid (0 kg HA ha-1) produced plants of lower HI. Likewise, more substantial

response was studied for N fertilization. N fertilizer at the rate of 240 kg ha-1 resulted

in higher HI, followed by 180 kg ha-1 N while lower harvest index was noted at 0 kg

ha-1 N (control plots of N).

Higher agronomic-nitrogen use efficiency (NUE-AE) was found in plots sown

with hybrid 55w65, followed by 3025 while Iqbal variety showed lower NUE-AE.

Regarding HA levels, HA application at the rate of 1.8 kg ha-1 resulted in higher NUE-

AE, followed by 1.2 kg ha-1 humic acid while 0 kg HA ha-1 resulted in lower NUE-AE.

Among N treatments, 180 kg ha-1 N recorded higher NUE-AE, followed by 240 and

120 kg ha-1 N respectively while no NUE was observed for control plots of nitrogen.

Likewise, greater partial factor productivity-nitrogen use efficiency (NUE-PFP) was

observed for those units treated with maize hybrid 55w65, followed by 3025 while Jalal

cultivar exhibited lower NUE-PFP. Regarding humic acid treatments, 1.8 kg HA ha-1

provided higher NUE-PFP, followed by 1.2 kg HA ha-1 while control plots of humic

acid resulted in lower NUE-PFP. As far as N application rates are concerned, 120 kg

ha-1 N provided higher NUE-PFP, followed by 180 and 240 kg ha-1 N respectively while

no NUE-PFP was recorded for 0 kg N ha-1. In a similar way, the net assimilation rate

(30-75 DAS) showed best result for OPV Iqbal due to its shorter life cycle and robust

growth habit, followed by 55w65 while Jalal variety produced lower NAR. While

200

considering humic acid levels, 1.8 kg HA ha-1 resulted in higher NAR in comparison to

control plots of humic acid (0 kg HA ha-1). Moreover, NAR also got improved with

enhancing N levels, where higher NAR was observed for 240 kg N ha-1 as compared to

lower levels of N fertilizer.

The soil phosphorous (P) and nitrogen (N) contents reported at maize harvest

were higher for Iqbal variety, followed by Jalal while it was lower for hybrid maize

genotypes i.e. 3025 and 55w65. The soil P and N contents increased linearly with

increase in the amount of humic acid and 1.8 kg HA ha-1 resulted in higher

concentration of P and N in the soil. Similarly, P and N concentration in the soil at

maize harvest increased with increase in N levels. The highest P and N contents were

recorded at 240 kg ha-1 N in comparison to control plots of N (0 kg N ha-1). Likewise,

the organic matter content of soil at maize harvest was higher in plots treated with OPV

Iqbal while it was lower in sub-subplots of 55w65. Regarding humic acid levels, 1.8 kg

HA ha-1 resulted in soils of higher organic matter (OM) content against control plots of

humic acid (0 kg HA ha-1). Similarly, higher soil OM was recorded at 240 kg N ha-1 as

compared to control plots of N. The higher net income (NI) was recorded for plots sown

with maize genotype 55w65 under higher rate of humic acid and N application while

OPV Jalal proved inferior in terms of NI. The genotype 3025 followed the maize hybid

55w65 regarding the higher net income while it had the highest value of VCR which

was at par with 55w65 under higher rate of humic acid and N application.

The results of the trials may be summarized for innately low fertility status soils

and resource poor farmers of the country. The high cost of inorganic fertilizers often

proves the most obstructive constraint in reaping the full yield potential of crops;

therefore integrated nutrient management is the only way for maximizing the crop

nutrients use efficiency and its productivity. The integration of HA and nitrogen with

high yielding maize genotypes may be a fundamental strategy for ameliorating the soil

fertility in cereal-based cropping systems of Pakistan. However, it demands careful and

exact evaluation in terms of varying soil fertility status under different agro-climatic

conditions. Participatory-based approaches are playing a central role in this regard to

estimate: 1). Whether HA amendment can virtually make a solid contribution to our

agricultural economy and 2). Does it present a long lasting solution to our farmers in

mitigating the constraints caused by indigent soil fertility status?

201

CONCLUSIONS

Based on the findings derived from our study, the following conclusions and

suggestions can be recommended:

1. The application of 1.8 kg humic acid ha-1 improved the OM status of the soil, and the

concentration of N and P in the soil at maize harvest. It also accelerated the net

assimilation rate (30-75 DAS), plant biomass production, leaf area index (LAI), crop

growth rate (CGR), absolute growth rate (AGR) and increased yield components of the

maize genotypes. It enhanced the agronomic-nitrogen use efficiency (NUE-AE) and

partial factor productivity-nitrogen use efficiency (NUE-PFP) of the crop. Moreover, it

also accelerated photosynthetic activity in association to longer seed fill duration, and

enhanced grain protein content (%) of maize genotypes.

2. Sole application of N at the level of 180 and 240 kg ha-1 provided better biomass

production of individual plants, and enhanced yield components as well as harvest

index of maize genotypes. However, 120 kg N ha-1 performed much better than control

plots.

3. In hybrids the integration of 1.8 kg HA + 240 kg N ha-1 brought much acceleration in

the soil fertility, maize yield and net economic returns per unit area while in case of

OPVs the combination of 1.8 kg HA + 180 kg N ha-1 proved highly economical for our

resource poor farmers due to more net income and higher value cost ratio (VCR) under

the agro-climatic conditions of Swabi region on sustainable basis.

4. The improved genotypes (hybrids) i.e. 55w65 and 3025 performed much better than the

open pollinated varieties (OPVs) of maize (Jalal and Iqbal) in terms of yield

components and N use efficiency.

RECOMMENDATIONS

In view of the above conclusions, the following recommendations are made.

1. To reap the potential benefits of our research work, the application of 1.8 kg

HA ha-1 is advised for our farming community at their field to enhance the yield

of their crops as it has a prolonged and long lasting effect on the fertility of soil.

2. The recommended use of 240 and 180 kg N ha-1 is observed to have a significant

and pronounced impact on the yield and yield components of maize hybrids and

OPVs respectively.

202

3. In hybrids the integration of 1.8 kg HA + 240 kg N ha-1 is recommended for

sustaining soil fertility, achieving better maize yield and receiving higher

economic returns per unit area. In case of OPVs the combination of 1.8 kg HA

+ 180 kg N ha-1 seems to be highly economical for our resource poor farmers

due to more net income and higher value cost ratio (VCR) under the agro-

climatic conditions of Swabi region on sustainable basis.

4. It is suggested for our maize growers to give preference to the cultivation of

maize hybrids over OPVs due to their higher yielding capacity, better nitrogen

use efficiency and value cost ratio/benefit cost ratio.

5. Further research is needed to find out a more pronounced effect of the higher

levels of humic acid in integration with N on the performance of maize

genotypes under various climatic conditions and soil types.

203

7. REFERENCES

Abakumov, E.V., Rodina, O.A. and Eskov, A.K., 2018. Humification and humic acid composition

of suspended soil in oligotrophous environments in South Vietnam. Applied and

Environmental Soil Science, 18, pp. 1-8.

Abbas, M.A., 2001. Genetics and crop improvement. General Agriculture, 2nd Ed. Emporium

Publisher, Lahore, Pakistan, pp. 218.

Abbasi, M.K. and Yousra, M., 2012. Synergistic effects of biofertilizer with organic and chemical

N sources in improving soil nutrient status and increasing growth and yield of wheat

grown under greenhouse conditions. Plant Biosystems-An International Journal Dealing

with all Aspects of Plant Biology, 146(sup1), pp. 181-189.

Abdel-Mawgoud, A.M.R., El-Greadly, N.H.M., Helmy, Y.I. and Singer, S.M., 2007. Responses

of tomato plants to different rates of humic-based fertilizer and NPK fertilization. Journal

of Applied Sciences Research, 3(2), pp. 169-174.

Abdelrahman, A.A. and Hoseney, R.C., 1984. Basis for hardness in pearl millet, grain sorghum,

and corn. Cereal Chemistry, 61(3), pp. 232-235.

Abd El-Maksoud, M.F. and Sarhan, A.A., 2008. Response of some maize hybrids to bio and

chemical nitrogen fertilization. Zagazig Journal of Agricultural Research, 35(3), pp. 497-

515.

Abouziena, H.F., El-Karmany, M.F., Singh, M. and Sharma, S.D., 2007. Effect of nitrogen

rates and weed control treatments on maize yield and associated weeds in sandy

soils. Weed Technology, 21(4), pp. 1049-1053.

Adani, F., Genevini, P., Zaccheo, P. and Zocchi, G., 1998. The effect of commercial humic acid

on tomato plant growth and mineral nutrition. Journal of Plant Nutrition, 21(3), pp. 561-

575.

Afzal, N. and Ahmad, S., 2009. Agricultural input use efficiency in Pakistan-Key issues and

reform areas. Managing Natural Resources for Sustaining Future Agriculture Research

Briefings, 1(3), pp. 1-12.

Ahmed, Howida E.A., 2011. Effect Of Spatial Distribution Of Plant Under Different Watering

Regimes On The Yield And Its Components Of Corn (Zea mays L.). M.Sc. Thesis, Agron.,

Deptt. Fac. Agric., Assiut Univ., Egypt.

204

Ahmad, N., 2010. Fertilizer scenario in Pakistan policies and development. In Proceedings of

Conference, Agricultural and Fertilizer Use (pp. 15-16).

Ahmad, N., Waheed, A., Hamid, F.S., Ahmad, N., Waheed, A. and Hamid, F.S., 2000.

Performance of maize cultivars under late sowing conditions. Pakistan Journal of

Biological Sciences, 3(12), pp. 2098-2100.

Ahmad, R., Ahmad, N., Ahmad, S. and Ahmad, T., 1993. Source-sink relationships in maize under

varying nitrogen regimes. Pakistan Journal of Agricultural Research, 14(2/3), pp. 173-

176.

Aiken, G.R., McKnight, D.M., Wershaw, R.L. and MacCarthy, P., 1985. An introduction to humic

substances in soil, sediment, and water. Wiley Inter Science, New York.

Akhtar, M.M., 2001. Effect Of Varying Levels Of Nitrogen On Growth And Yield Performance Of

Two New Wheat Cultivars. M.Sc (Hons) thesis, Deptt. of Agron., Univ. of Agri.

Faisalabad, pp. 84-86.

Akmal, M., Rehman, H., Farhatullah, M.A. and Akbar, H., 2010. Response of maize varieties to

nitrogen application for leaf area profile, crop growth, yield and yield components.

Pakistan Journal of Botany, 42(3), pp. 1941-1947.

Akram, M., Ashraf, M.Y., Waraich, E.A., Hussain, M., Hussain, N. and Mallahi, A.R., 2010.

Performance of autumn planted maize (Zea mays L.) hybrids at various nitrogen levels

under salt affected soils. Soil and Environment, 29(1), pp. 23-32.

Alam, M.M., Muriith, F. and Islam, M.N., 2003. Effects of sulphur and nitrogen on the yield and

seed quality of maize (cv. Barnali). Journal of Biological Sciences, 3, pp. 643-654.

Albayrak, S. and Camas, N., 2005. Effects of different levels and application times of humic acid

on root and leaf yield and yield components of forage turnip (Brassica rapa L.). Journal

of Agronomy, 4(2), pp. 130-133.

Ali, K., Jan, A. and Khan, M.J., 2015. Pheno-morphological traits of canola as influenced by

nitrogen and green manuring crops (species, parts and age) under semiarid condition. Pure

and Applied Biology, 4(3), p. 362.

Ali, K., Munsif, F., Zubair, M., Hussain, Z., Shahid, M., Din, I.U. and Khan, N., 2011.

Management of organic and inorganic nitrogen for different maize varieties. Sarhad

Journal of Agriculture, 27(4), pp. 525-529.

205

Aliu, S., Sh, F. and Rozman, L., 2010. Variation of physiological traits and yield components of

some maize hybrid (Zea mays L.) in agroecological conditions of Kosovo. Acta

Agriculturae Slovenica, 95(1), pp. 35-41.

Alley, M.M., Martz Jr, M.E., Davis, P.H. and Hammons, J.L., 2009. Nitrogen and Phosphorous

Fertilization of Corn: Virginia Cooperative Extension. Virginia Tech, and Virginia State

University, Pp. 424-427.

Almas, L.K., 2009. Partial factor productivity, agronomic efficiency, and economic analyses of

maize in wheat-maize cropping system in Pakistan. In 2009 Annual Meeting, January 31-

February 3, 2009, Atlanta, Georgia (No. 46747). Southern Agricultural Economics

Association.

Amandeep, K., Seema, B., Gill, G.K. and Mahesh, K., 2012. Effect of nitrogen fertilizers on

radiation use efficiency, crop growth and yield in some maize (Zea mays L.)

genotypes. Maydica, 57(1), pp. 75-82.

Amanulah, A., 2004. Physiology, Partitioning Of Assimilates And Yield of Maize As Affected By

Plant Density, Rate And Timing of Nitrogen Application (Doctoral dissertation, Univ. of

Agric., Peshawar).

Amanullah, Khattak, R.A. and Khalil, S.K., 2009. Plant density and nitrogen effects on maize

phenology and grain yield. Journal of Plant Nutrition, 32(2), pp. 246-260.

Amujoyegbe, B.J., Opabode, J.T. and Olayinka, A., 2007. Effect of organic and inorganic fertilizer

on yield and chlorophyll content of maize (Zea mays L.) and sorghum (Sorghum bicolour

L.) Moench. African Journal of Biotechnology, 6(16), pp. 1869-1873.

Andrade, F.H., Ortegiu, M.E. and Vega, C., 2000. Intercepted radiation at flowering and kernel

number in maize. Agronomy Journal, 92(1), pp. 92-97.

Anees, M.U., Khan, H.Z., Ahmed, Z., 2016. Role of organic amendments and micronutrients in

maize (Zea mays L.) sown on calcareous soils. American-Eurasian Journal of

Agricultural and Environmental Sciences, 16(4), pp. 795-800.

Anjum, K., Khan, G.S., Afzal, M. and Khan, Z.H., 2011. Economic comparison of agriculture

with agroforestry in tehsil Kamalia, district Toba Tek Singh, Pakistan. Journal of

Agricultural Research, 49(4), pp. 551-561.

206

Anzoua, K.G., Junichi, K., Toshihiro, H., Kazuto, I. and Yutaka, J., 2010. Genetic improvements

for high yield and low soil nitrogen tolerance in rice (Oryza Sativa L.) under a cold

environment. Field Crops Research, 116(1-2), pp. 38-45.

Aragão, C.A., Dantas, B.F., Alves, E., Cataneo, A.C., Cavariani, C. and Nakagawa, J., 2003.

Atividade amilolítica e qualidade fisiológica de sementes armazenadas de milho super

doce tratadas com ácido giberélico. Revista Brasileira de Sementes, 25(1), pp. 43-48.

Arif, M., Amin, I., Jan, M.T., Munir, I., Nawab, K., Khan, N.U. and Marwat, K.B., 2010. Effect

of plant population and nitrogen levels and methods of application on ear characters and

yield of maize. Pakistan Journal of Botany, 42(3), pp. 1959-1967.

Arshad, M., 2003. Effect Of Different Irrigations And Nitrogen Levels On Growth and Yield Of

Maize. M.Sc. (Hons). Thesis, Univ. of Agri. Faisalabad, Pakistan.

Ashraf, M.W., Saqib, N. and Sarfaraz, T.B., 2005. Biological effect of bio-fertilizer humic acid

on mung beans (Vigna radiate L.). Journal of Bioscience and Biotechnology, 2(3), pp.

737-739.

Ashraf, S.D. and Nelly, M.C., 1994. The effects of growing beans together with maize on

incidence of bean diseases and pests. Netherlands Journal of Plant Pathology, 78, pp. 12-

18.

Aslam, M., Iqbal, A., Zamir, M.I., Mubeen, M. and Amin, M., 2011. Effect of different nitrogen

levels and seed rates on yield and quality of maize fodder. Crop and Environment, 2(2),

pp. 47-51.

Atiyeh, R.M., Lee, S., Edwards, C.A., Arancon, N.Q. and Metzger, J.D., 2002. The influence of

humic acids derived from earthworm-processed organic wastes on plant growth.

Bioresource Technology, 84(1), pp. 7-14.

Ayas, H. and Gulser, F., 2005. The effect of sulfur and humic acid on yield components and

macronutrient contents of spinach (Spinacia Oleracea Var. Spinoza). Journal of


Ayeni, L.S. and Adetunji, M.T., 2010. Integrated application of poultry manure and mineral

fertilizer on soil chemical properties, nutrient uptake, yield and growth components of

maize. Journal of Nature and Science, 8(1), pp. 60-67.

207

Ayoola, O.T. and Makinde, E.A., 2009. Maize growth, yield and soil nutrient changes with N-

enriched organic fertilizers. African Journal of Food, Agriculture, Nutrition and

Development, 9(1), pp. 580-592.

Ayub, M., Ahmad, R., Nadeem, M.A., Ahmad, B. and Khan, R.M.A., 2003. Effect of different

levels of nitrogen and seed rates on growth, yield and quality of maize fodder. Pakistan

Journal of Agricultural Sciences, 40(3-4), pp. 140-143.

Ayub, M., Nadeem, M.A., Sharar, M.S. and Mahmood, N., 2002. Response of maize (Zea mays

L.) fodder to different levels of nitrogen and phosphorus. Asian Journal of Plant Sciences,

1(4), pp. 352-354.

Azad, M.A.K., Biswas, B.K., Alam, N. and Alam, S.S., 2012. Genetic diversity in maize (Zea

mays L.) inbred lines. The Agriculturists, 10(1), pp. 64-70.

Azadgoleh, M.A.E. and Kazmi, Z., 2007. A study of the planting pattern and density effects on

yield and physiological growth parameters in two corn cultivars. Ecology, Environment

and Conservation, 13(3), pp. 467-472.

Azam, F., Iqbal, M.M., Inayatullah, C. and Malik, K.A., 2001. Technologies for sustainable

agriculture. Nuclear Institute for Agriculture and Biology, Faisalabad, pp. 144.

Azam, S., Ali, M., Amin, M., Bibi, S. and Arif, M., 2007. Effect of plant population on maize

hybrids. Journal of Agricultural and Biological Sciences, 2(1), pp. 13-20.

Azarpour, E., Danesh, R.K., Mohammadi, S., Bozorgi, H.R. and Moraditochaee, M., 2011. Effects

of nitrogen fertilizer under foliar spraying of humic acid on yield and yield components of

cowpea (Vigna unguiculata). World Applied Sciences Journal, 13(6), pp. 1445-1449.

Azarpour, E., Moraditochaee, M. and Bozorg. H.R., 2014. Effect of nitrogen fertilizer

management on growth analysis of rice cultivars. International Journal of Biosciences,

4(5), pp. 35-47.

Azarpour, E., Motamed, M.K., Moraditochaee, M. and Bozorgi, H.R., 2012. Effects of bio,

mineral nitrogen fertilizer management, under humic acid foliar spraying on fruit yield

and several traits of eggplant (Solanum melongena L.). African Journal of Agricultural

Research, 7(7), pp. 1104-1109.

Azeem, K., Khalil, S.K., Khan, F., Shah, S., Qahar, A., Sharif, M. and Zamin, M., 2014.

Phenology, yield and yield components of maize as affected by humic acid and nitrogen.

Journal of Agricultural Sciences, 6(7), pp. 286-293.

208

Azeem, K., Shah, S., Ahmad, N., Shah, S.T., Khan, F., Arafat, Y., Naz, F., Azeem, I. and Ilyas,

M., 2015. Physiological indices, biomass and economic yield of maize influenced by

humic acid and nitrogen levels. Basic Research Journals of Agricultural Science and

Review, 4(6), pp. 158-163.

Bakht, J., Siddique, M.F., Shafi, M., Akbar, H., Tariq, M., Khan, N., Zubair, M. and Yousef, M.,

2007. Effect of planting methods and nitrogen levels on the yield and yield components

of maize. Sarhad Journal of Agriculture, 23(3), pp. 253-259.

Bakry, B.A., Elewa., T.A., El-Kramany, M.F. and Wali, A.M., 2013. Effect of humic and ascorbic

acids foliar application on yield and yield components of two wheat cultivars grown under

newly reclaimed sandy soil. International Journal of Agronomy and Plant Production,

4(6), pp. 1125-1133.

Bakry, M.A., Soliman, Y.R. and Moussa, S.A., 2009. Importance of micronutrients, organic

manure and biofertilizer for improving maize yield and its components grown in desert

sandy soils. Research Journal of Agriculture and Biological Sciences, 5(1), pp. 16-23.

Baldock, J.A. and Nelson, P.N., 2000. Soil organic matter. In ‘Handbook of soil science’. (Ed.

ME Sumner), pp. B25–B84.

Ball, D.F., 1964. Loss on ignition as an estimate of organic matter and organic carbon in non‐

calcareous soils. European Journal of Soil Science, 15(1), pp. 84-92.

Banerjee, A., Datta, J.K. and Mondal, N.K., 2012. Changes in morpho-physiological traits of

mustard under the influence of different fertilizers and plant growth regulator cycocel.

Journal of the Saudi Society of Agricultural Sciences, 11(2), pp. 89-97.

Banfield, J.F. and Hamers, R.J., 1997. Processes at minerals and surfaces with relevance to

microorganisms and prebiotic synthesis. Reviews in Mineralogy and Geochemistry, 35(1),

pp. 81-122.

Bangarwa, A.S., Kairon, M.S. and Singh, K.P., 1988. Effect of plant density and level and

proportion of nitrogen fertilization on growth, yield and yield component of winter maize

(Zea mays L.). Indian Journal of Agricultural Sciences, 58(11), pp. 854-856.

Bänziger, M., Betran, F.J. and Lafitte, H.R., 1997. Efficiency of high-nitrogen selection

environments for improving maize for low-nitrogen target environments. Crop Science,

37(4), pp.1103-1109.

209

Beadle, C.L., 1993. Growth analysis. In Photosynthesis and Production in a Changing

Environment (pp. 36-46). Springer, Dordrecht.

Begna, S.H., Hamilton, R.I., Dwyer, L.M., Stewart, D.W., Cloutier, D., Assemat, L., Foroutan-

Pour, K. and Smith, D.L., 2001. Morphology and yield response to weed pressure by corn

hybrids differing in canopy architecture. European Journal of Agronomy, 14(4), pp. 293-

302.

Bewely, J.D. and Black. M., 1994. Seed Physiology, Development and Germination, 2nd Ed.

Plenum Press, New York, pp. 1-33.

Bhattacharyya, R., Kundu, S., Prakash V. and Gupta, H.S., 2008. Sustainability under combined

application of mineral and organic fertilizers in a rainfed soybean-wheat system of the

Indian Himalayas. European Journal of Agronomy, 28(1), pp. 33-46.

Billingham, K., 2012. Humic products potential or presumption for agriculture? Can humic

products improve my soil. In Proceedings of the 27th Annual Conference of the Grassland

Society of NSW Inc., Orange, NSW, Australia, pp. 24-26.

Boehlje, M.D. and Eidman, V.R., 1984. Farm management. John Wiley and Sons, New York.

Borrás, L. and Gambín, B.L., 2010. Trait dissection of maize kernel weight: Towards integrating

hierarchical scales using a plant growth approach. Field Crops Research, 118(1), pp. 1-

12.

Borrás, L., Zinselmeier, C., Senior, M.L., Westgate, M.E. and Muszynski, M.G., 2009.

Characterization of grain-filling patterns in diverse maize germplasm. Crop Science,

49(3), pp. 999-1009.

Brady, N.C. and Weil, R.R., 1990. The Nature and Properties of Soil. 10th Ed. Macmillan

Publications, Co. Ltd., New York, pp. 364.

Bray, E.A., Bailey-Serres, J. and Weretilnyk, E., 2000. Responses to abiotic stresses.

Biochemistry and molecular biology of plants, pp. 1158-1203.

Bremner, J.M. and Mulvaney, C.S., 1982. Nitrogen-total. Methods of Soil Analysis. Part 2.

Chemical and Microbiological Properties, pp. 595-624.

Bumb, B.L. and Baanante, C.A., 1996. The Role of Fertilizer in Sustaining Food Security and

Protecting the Environment to 2020. Intl Food Policy Res Inst.

210

Burger, M. and Jackson, L.E., 2003. Microbial immobilization of ammonium and nitrate in

relation to ammonification and nitrification rates in organic and conventional cropping

systems. Soil Biology and Biochemistry, 35(1), pp. 29-36.

Buyukkeskin, T. and Akinci, S., 2011. The effects of humic acid on above-ground parts of broad

bean (Vicia faba L.) seedlings under Al (3+) toxicity. Fresenius Environmental Bulletin,

20(3), pp. 539-548.

Byerlee, D., Anandajayasekeram, P., Diallo, A., Gelaw, B., Heisey, P.W., Lopez-Pereira, M.,

Mwangi, W., Smale, M., Tripp, R. and Waddington, S., 1994. Maize Research in Sub-

Saharan Africa: An Overview of Past Impacts and Future Prospects. Mexico, DF:

CIMMYT.

Camara, K.M., Payne, W.A. and Rasmussen, P.E., 2003. Long-term effects of tillage, nitrogen,

and rainfall on winter wheat yields in the Pacific Northwest. Agronomy Journal, 95(4),

pp. 828-835.

Canellas, L.P. and Olivares, F.L., 2014. Physiological responses to humic substances as plant

growth promoter. Chemical and Biological Technologies in Agriculture, 1(1), p. 3.

Canellas, L.P., Olivares, F.L., Okorokova-Façanha, A.L. and Façanha, A.R., 2002. Humic acids

isolated from earthworm compost enhance root elongation, lateral root emergence, and

plasma membrane H+-ATPase activity in maize roots. Plant Physiology, 130(4), pp. 1951-

1957.

Canellas, L.P., Teixeira Junior, L.R.L., Dobbss, L.B., Silva, C.A., Medici, L.O., Zandonadi, D.B.

and Façanha, A.R., 2008. Humic acids crossinteractions with root and organic

acids. Annals of Applied Biology, 153(2), pp. 157-166.

Canfield, D.E., Glazer, A.N. and Falkowski, P.G., 2010. The evolution and future of earth’s

nitrogen cycle. Science, 330(6001), pp. 192-196.

Cárcova, J. and Otegui, M.E., 2001. Ear temperature and pollination timing effects on maize

kernel set. Crop Science, 41(6), pp. 1809-1815.

Cathcart, R.J. and Swanton, C.J., 2003. Nitrogen management will influence threshold values of

green foxtail (Setaria viridis) in corn. Weed Science, 51(6), pp. 975-986.

Celik, H., Katkat, A.V., Așık, B.B. and Turan, M.A., 2010. Effects of humus on growth and

nutrient uptake of maize under saline and calcareous soil conditions. Žemdirbystė

(Agriculture), 97(4), pp. 15-22.

211

Celik, H., Katkat, A.V., Aşık, B.B. and Turan, M.A., 2011. Effect of foliar-applied humic acid to

dry weight and mineral nutrient uptake of maize under calcareous soil

conditions. Communications in Soil Science and Plant Analysis, 42(1), pp. 29-38.

Chaudhry, A.N., Latif, M.I., Haroon-ur-Rasheed, M. and Jilani, G., 2005. Profitability increase in

maize production through fertilizer management anddefoliation under rainfed

cropping. International Journal of Biology and Biotechnology (Pakistan), 2(4), pp. 1007-

1012.

Cheema, M.A., Farhad, W., Saleem, M.F., Khan, H.Z., Munir, A., Wahid, M.A., Rasul, F. and

Hammad, H.M., 2010. Nitrogen management strategies for sustainable maize production.

Crop and Environment, 1(1), pp. 49-52.

Cheetham, H., Millner, J. and Hardacre, A., 2006. The effect of nitrogen fertilisation on maize

grain quality and yield. Agronomy New Zealand, 36, pp. 71-84.

Chen, Y., Clapp, C.E. and Magen, H., 2004. Mechanisms of plant growth stimulation by humic

substances: The role of organo-iron complexes. Soil Science and Plant Nutrition, 50(7),

pp. 1089-1095.

Chen, Y., Clapp, C.E., Magen, H. and Cline, V.W., 1999. Stimulation of plant growth by humic

substances: Effects on iron availability. In Understanding Humic Substances (pp. 255-

263).

Chen, Y., Magen, H. and Clapp, C.E., 2001, March. Plant growth stimulation by humic substances

and their complexes with iron. International Fertiliser Society.

Chen, Y., De Nobili, M. and Aviad, T., 2004. Stimulatory effect of humic substances on plant

growth. In Soil Organic Matter in Sustainable Agriculture. Magdoff, F. and Weil R.R.

(Eds). Pp. 103-130.

Christopher, S.F. and Lal, R., 2007. Nitrogen management affects carbon sequestration in

North American cropland soils. Critical Reviews in Plant Sciences, 26(1), pp. 45-64.

Chung, R.S., Wang, C.H., Wang, C.W. and Wang, Y.P., 2000. Influence of organic matter and

inorganic fertilizer on the growth and nitrogen accumulation of corn plants. Journal of

Plant Nutrition, 23(3), pp. 297-311.

Cirilo, A.G., Dardanelli, J., Balzarini, M., Andrade, F.H., Cantarero, M., Luque, S. and Pedrol.

H.M., 2009. Morphophysiological traits associated with maize adaptations to

environments differing in nitrogen availability. Field Crop Research, 113(2), pp. 116-124.

212

Cisse, L. and Amar, B., 2000. The importance of phosphatic fertilizer for increased crop

production in developing countries. In Proceedings of the AFA 6th International Annual

Conference (pp. 1-7). Casablanca,, Morocco: World Phosphate Institute.

Clarkson, D.T., 1985. Factors affecting mineral nutrient acquisition by plants. Annual Review of

Plant Physiology, 36(1), pp. 77-115.

Coleman, D.C. and Wall, D.H., 2007. Fauna: the engine for microbial activity and transport.

In Soil Microbiology, Ecology and Biochemistry (3rd Edition) (pp. 163-191).

Cooke, G.W., 1987. Fertilizer use efficiency: Maximising fertilizer efficiency by overcoming

constraints to crop growth. Journal of Plant Nutrition, 10(9-16), pp. 1357-1369.

Correia, C.M., Coutinho, J.F., Björn, L.O. and Torres-Pereira, J.M., 2000. Ultraviolet-B radiation

and nitrogen effects on growth and yield of maize under Mediterranean field

conditions. European Journal of Agronomy, 12(2), pp. 117-125.

Cox, W.J., Kalonge, S., Cherney, D.J.R. and Reid, W.S., 1993. Growth, yield, and quality of

forage maize under different nitrogen management practices. Agronomy Journal, 85(2),

pp. 341-347.

Craufurd, P.Q., Wheeler, T.R., Ellis, R.H., Summerfield, R.J. and Williams, J.H., 1999. Effect of

temperature and water deficit on water-use efficiency, carbon isotope discrimination, and

specific leaf area in peanut. Crop Science, 39(1), pp. 136-142.

Crosbie, T.M., 1982. Changes in physiological traits associated with long-term breeding efforts

to improve grain yield of maize. In Proceedings of the Annual Corn and Sorghum Industry

Research Conference-American Seed Trade Association, Corn and Sorghum Division,

Corn and Sorghum Research Conference (USA).

Dahal, S., Karki, T.B., Amgain, L.P. and Bhattachan, B.K., 2014. Tillage, residue, fertilizer and

weed management on phenology and yield of spring maize in Terai, Nepal. International

Jounral of Applied Sciences and Biotechnology, 2(3), pp. 328-335.

Daur, I. and Bakhashwain, A.A., f2013. Effect of humic acid on growth and quality of maize

fodder production. Pakistan Journal of Botany, 45(S1), pp. 21-25.

Dawadi, D.R. and Sah, S.K., 2012. Growth and yield of hybrid maize (Zea mays L.) in relation to

planting density and nitrogen levels during winter season in Nepal. Tropical Agricultural

Research, 23(3), pp. 218-227.

213

Davis, J.H.C. and Garcia, S., 1983. Competitive ability and growth habit of indeterminate beans

and maize for intercropping. Field Crops Research, 6, pp. 59-75.

Day, K.S., Thornton, R. and Kreeft, H., 2000. Humic acid products for improved phosphorus

fertilizer management. Special Publication-Royal Society of Chemistry, 259, pp. 321-325.

Deksissa, T., Short, I. and Allen, J., 2008. Effect of soil amendment with compost on growth and

water use efficiency of Amaranth. In Proceedings of the UCOWR/NIWR Annual

Conference: International Water Resources: Challenges for the 21st Century and Water

Resources Education.

Delate, K. and Camberdella, C.A., 2004. Agro-ecosystem performance during transition to

certified organic grain production. Agronomy Journal, 96(5), pp. 1288-1298.

Delfine, S., Tognetti, R., Desiderio, E. and Alvino, A., 2005. Effect of foliar application of N and

humic acids on growth and yield of durum wheat. Agronomy for Sustainable

Development, 25(2), pp. 183-191.

Derby, N.E., Casey, F.X., Knighton, R.E. and Steel, D.D., 2004. Midseason nitrogen fertility

management for corn based on weather and yield prediction. Agronomy Journal, 96(2),

pp. 494-501.

De-Sclaux, D., Huynh, T.T. and Roumet, P., 2000. Identification of soybean plant characteristics

that indicate the timing of drought stress. Crop Science, 40(3), pp. 716-722.

Dev, S.P. and Bhardwaj, K.K.R., 1995. Effect of crop wastes and nitrogen levels on biomass

production and nitrogen uptake in wheat-maize sequence. Annals of Agricultural

Research, 16, pp. 264-267.

Diker, K. and Bausch, W.C., 2003. Potential use of nitrogen reflectance index to estimate plant

parameters and yield of maize. Biosystems Engineering, 85(4), pp. 437-447.

Dilip, S. and Nepalia, V., 2009. Influence of integrated nutrient management on quality protein

maize (Zea mays) productivity and soils of southern Rajasthan. Indian Journal of

Agricultural Sciences, 79(12), pp. 1020-1022.

Dilshad, M., Lone, M.I., Jilani, G., Malik, M.A., Yousaf, M., Khalid, R. and Shamim, F., 2011.

Sustaining soil productivity by integrated plant nutrient management in wheat based

cropping system under rainfed conditions. Pakistan Journal of Scientific and Industrial

Research, 54, pp. 9-17.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwio362kmbnVAhUBrRoKHRJPCmwQFggnMAA&url=http%3A%2F%2Fwww.pjsir.org%2F&usg=AFQjCNF9_-UntLO4BqLcyXSbCpCHhfvhlQ

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwio362kmbnVAhUBrRoKHRJPCmwQFggnMAA&url=http%3A%2F%2Fwww.pjsir.org%2F&usg=AFQjCNF9_-UntLO4BqLcyXSbCpCHhfvhlQ

214

Dilshad, M.D., Lone, M.I., Jilani, G., Malik, M.A., Yousaf, M., Khalid, R. and Shamim, F., 2010.

Integrated plant nutrient management (IPNM) on maize under rainfed condition. Pakistan

Journal of Nutrition, 9(9), pp. 896-901.

Dobermann, A., 2007. Nutrient use efficiency-measurement and management. Fertilizer Best

Management Practices, 1.

Dong, H., Zhang, G., Jiang, H., Yu, B., Chapman, L.R., Lucas, C.R. and Fields, M.W., 2006.

Microbial diversity in sediments of saline Qinghai lake, China: linking geochemical

controls to microbial ecology. Microbial Ecology, 51(1), pp. 65-82.

Duncan, R.R. and Baligar, V.C., 1990. Genetics, breeding, and physiological mechanisms of

nutrient uptake and use efficiency: an overview. In Crops as Enhancers of Nutrient Use

(pp. 3-35).

Duvick, D.N., 1992. Genetic contributions to advances in yield of US maize. Maydica (Italy).

Dwyer, L.M., Anderson, A.M., Stewart, D.W., Ma, B.L. and Tollenaar, M., 1995. Changes in

maize hybrid photosynthetic response to leaf nitrogen, from pre-anthesis to grain filling.

Agronomy Journal, 87(6), pp. 1221-1225.

Earl, H.J. and Tollenaar, M., 1997. Maize leaf absorptance of photosynthetically active radiation

and its estimation using a chlorophyll meter. Crop Science, 37(2), pp. 436-440.

Echarte, L., Andrade, F.H., Sadras, V.O. and Abbate, P., 2006. Kernel weight and its response to

source manipulations during grain filling in Argentinean maize hybrids released in

different decades. Field Crops Research, 96(2-3), pp. 307-312.

Echarte, L., Luque, S., Andrade, F.H., Sadras, V.O., Cirilo, A., Otegui, M.E. and Vega, C.R.C.,

2000. Response of maize kernel number to plant density in Argentinean hybrids released

between 1965 and 1993. Field Crops Research, 68(1), pp. 1-8.

Edmeades, G.O., Bolaños, J., Hernandez, M. and Bello, S., 1993. Causes for silk delay in a

lowland tropical maize population. Crop Science, 33(5), pp. 1029-1035.

Edwards, J.H. and Someshwar, A.V., 2000. Chemical, physical, and biological characteristic of

agricultural and forest by-products for land application. Land Application of Agricultural,

Industrial, and Municipal By-Products, pp. 1-62.

215

Effa, E.B., Uwah, D.F., Iwo, G.A., Obok, E.E. and Ukoha, G.O., 2012. Yield performance of

Popcorn (Zea mays L. everta) under lime and nitrogen fertilization on an acid soil. Journal

of Agricultural Science, 4(10), pp. 12-19.

Eghball, B. and Maranville, J.W., 1991. Interactive effects of water and N stresses on N utilization

efficiency, leaf water status and yield of com genotypes. Communication in Soil Science

and Plant Analysis, 22(13-14), pp. 1367-1382.

Eghball, B. and Power, J.F., 1999. Composted and noncomposted manure application to

conventional and no-tillage systems: corn yield and nitrogen uptake. Agronomy

Journal, 91(5), pp. 819-825.

El-Akabawy, M.A., 2000. Effect of some biofertilizers and farmyard manure on yield and nutrient

uptake of Egyptian clover grown on loamy sandy soil. Egyptian Journal of Agricultural

Research, 78(5), pp. 1811-1819.

El-Gizawy, N.K.B. and Salem, H.M., 2010. Influence of nitrogen sources on yield and its

components of some maize varieties. World Journal of Agricultural Sciences, 6(2), pp.

218-223.

El-Hassan, W.H.A., Hafez, E.M., Ghareib, A.A.A., Freeg, M.R. and Seleiman, M.F., 2014.

Impact of nitrogen fertilisation and irrigation on water utilization efficiency, N

accumulation, growth and yields of Zea mays L. Journal of Food, Agriculture and

Environment, 12(3&4), pp. 217-222.

El-Mekser, H., Mohamed, Z.E.O.M. and Ali, M., 2014. Influence of Humic Acid and Some

Micronutrients on Yellow Corn Yield and Quality. World Applied Sciences Journal,

32(1), pp. 01-11.

Emad, M.H., Aboukhadrah, S.H., Sorour, S.G.R. and Yousef, A.R., 2012. Comparison of

agronomical and physiological nitrogen use efficiency in three cultivars of wheat as

affected by different levels of N sources. Pp. 130-145.

Esmaeilzadeh, J. and Ahangar, A.G., 2014. Influence of soil organic matter content on soil

physical, chemical and biological properties. International Journal of Plant, Animal and

Environmental Sciences, 4(4), pp. 244-252.

Eyheraguibel, B., Silvestre, J. and Morard, P., 2008. Effects of humic substances derived from

organic waste enhancement on the growth and mineral nutrition of maize. Bioresource

Technology, 99(10), pp. 4206-4212.

216

Fagbenro, J.A. and Agboola, A.A., 1993. Effect of different levels of humic acid on the growth

and nutrient uptake of teak seedlings. Journal of Plant Nutrition, 16(8), pp. 1465-1483.

Fageria, N.K., Baligar, V.C. and Clark, R.B., 2006. Root growth parameters and methods of

measurement. Root Architecture. Physiology of Crop Production, pp. 23-59.

Faheed, F., Mohamed, E. and Mahmoud, H., 2016. Improvement of maize crop yield (Zea mays

L.) by using of nitrogen fertilization and foliar spray of some activators. Journal of

Ecology of Health and Environment, 4(1), pp. 33-47.

Fahramand, M., Moradi, H., Noori, M., Sobhkhizi, A., Adibian, M., Abdollahi, S. and Rigi, K.,

2014. Influence of humic acid on increase yield of plants and soil properties. International

Journal of Farming and Allied Sciences, 3(3), pp. 339-341.

Faisal, S., Ahmad, B., Akhtar, K., Ali, S. and Ullah, I., 2015. Effect of organic and inorganic

fertilizers on penology of maize varieties. Pure and Applied Biology, 4(3), pp. 434-440.

Farhad, W., Cheema, M.A., Saleem, M.F., Hammad, H.M. and Bilal, M.F., 2011. Response of

maize hybrids to composted and non-composted poultry manure under different irrigation

regimes. International Journal of Agriculture and Biology, 13(6), pp. 923-928.

Farhad, W., Saleem, M.F., Cheema, M.A. and Hammad, H.M., 2009. Effect of poultry manure

levels on the productivity of spring maize (Zea may L.). Journal of Animal and Plant

Sciences, 19(3), pp. 122-125.

Farnham, D.E., 2001. Row spacing, plant density and hybrid effects on corn grain yield and

moisture. Agronomy Journal, 93(5), pp. 1049-1053.

Farnia, A. and Ashjardi, V.K., 2015. Effect of nitrogen biofertilizers on yield and yield

components of different maize (Zea mays L.) cultivars. International Journal of Life

Sciences, 9(5), pp. 117-121.

Fava, F., Berselli, S., Conte, P., Piccolo, A. and Marchetti, L., 2004. Effects of humic substances

and soya lecithin on the aerobic bioremediation of a soil historically contaminated by

polycyclic aromatic hydrocarbons (PAHs). Biotechnology and Bioengineering, 88(2), pp.

214-223.

Figliolia, A., Benedetti, A., Izza, C., Indiati, R., Rea, E., Alianiello, F., Canali, S., Biondi, F.A.,

Pierandrei, F. and Moretti, R., 1994. Effects of fertilization with humic acids on soil and

plant metabolism: a multidisciplinary approach. Note I: crop production. Pp. 579-584.

217

Frank, K.D. and Roeth, F.W., 1996. Using soil organic matter to help make fertilizer and pesticide

recommendations. Soil Organic Matter: Analysis and Interpretation, pp. 33-40.

Freebairn, B., 2005. Productive dual purpose winter wheat. Available online at

www.agric.nsw.gov.au

Gallagher, J.N. and Biscoe, P.V., 1978. A physiological analysis of cereal yield. II. Partitioning

of dry matter. Agricultural Progress, 53, pp. 51-70.

Gambín, B.L., Borrás, L. and Otegui, M.E., 2006. Source-sink relations and kernel weight

differences in maize temperate hybrids. Field Crops Research, 95(2), pp. 316-326.

Gatabazi, A., 2014. Nitrogen, Phosphorus And Potassium Availability as Influenced By Humate

And Fulvate Soil Amendment (Doctoral dissertation, University of Pretoria).

Fageria, N.K., Baligar, V.C. and Clark, R., 2006. Physiology of crop production. CRC Press.

Garnett, T., Plett, D., Conn, V., Conn, S., Rabie, H., Rafalski, J.A., Dhugga, K., Tester, M.A. and

Kaiser, B.N., 2015. Variation for N uptake system in maize: genotypic response to N

supply. Frontiers in Plant Science, 6(936), pp. 1-13.

Ghabbour, E.A., Davies, G. and Clapp, C.E., 2001. 6: An organic matter trail: Polysaccharides

to waste management to nitrogen/carbon to humic substances. In Humic Substances

(pp. 3-18).

Ghaly, A.E. and Ramakrishnan, V.V., 2015. Nitrogen sources and cycling in the ecosystem and

its role in air, water and soil pollution: a critical review. Journal of Pollution Effects and

Control, pp. 1-26.

Ghazal, F.M., El-Koomy, M.B.A., Abdel-Kawi, K.H.A. and Soliman, M.M., 2013b. Impact of

cyanobacteria, humic acid and nitrogen levels on maize (Zea mays L.) yield and biological

activity of the rhizosphere in sandy soils. Journal of American Science, 9(2), pp. 46-55.

Gholami, B., Mohammadinasab, A.D. Amini, R. and Shakiba, M.R., 2014. Morphophysiological

characteristics of corn (Zea mays) affected by copper and humic acid. International

Journal of Biosciences, 5(7), pp, 176-183.

Ghorbani, S., Khazaei, H.R., Kafi, M. and Bannayan, A.M., 2010. Effect of humic acid application

with irrigation water on yield and yield components of corn (Zea mays L.). Journal of

Agroecology, 2, pp. 111-118.

218

Girmay, G., Singh, B.R., Mitiku, H., Borresen, T. and Lal, R., 2008. Carbon stocks in Ethiopian

soils in relation to land use and soil management. Land Degradation and Development,

19(4), pp. 351-367.

Gökmen, S., Sencar, Ö. and Sakin, M.A., 2001. Response of popcorn (Zea mays L. everta) to

nitrogen rates and plant densities. Turkish Journal of Agriculture and Forestry, 25(1), pp.

15-23.

Gomaa, M.A., Radwan, F.I., Khalil, G.A.M., Kandil, E.E. and El-Saber, M.M., 2014. Impact of

humic acid application on productivity of some maize hybrids under water stress

conditions. Middle East Journal of Applied Sciences, 4(3), pp. 668-673.

Good, A.G., Shrawat, A.K. and Muench, D.G., 2004. Can less yield more? Is reducing nutrient

input into the environment compatible with maintaining crop production? Trends in Plant

Science, 9(12), pp. 597-605.

Govt. of Pakistan., 2009. Pakistan Economic Survey 2008-09. Ministry of Finance, Islamabad,

Pakistan. Pp. 22.

Graham, S.J. and Vance, Y.R., 2000. The glycine-glomus-rhizobium symbiosis IV. Interactions

between mycorrhizal and nitrogen-fixing endophytes. Plant Cell Environment, 10, pp.

607-617.

Grant, C.D., 2003. The Nature and Properties of Soils: NC Brady, RR Weil, Prentice Hall,

Upper Saddle River, NJ, 960. Agriculture, Ecosystems and Environment, 1(95), pp.

393-394.

Green, C.J. and Blackmer, A.M., 1995. Residue decomposition effects on nitrogen availability to

corn following corn or soybean. Soil Science Society of America Journal, 59, pp. 1065-

1070.

Grzesiak, S., 2001. Genotypic variation between maize (Zea mays L.) single-cross hybrids in

response to drought stress. Acta Physiologiae Plantarum, 23(4), pp. 443-456.

Gul, B., Marwat, K.B., Khan, M.A. and Khan, H., 2014. Impact of tillage, plant population and

mulches on phenological characters of maize. Pakistan Journal of Botany, 46(2), pp. 549-

554.

Gulser, F., Sonmez, F. and Boysan, S., 2010. Effects of calcium nitrate and humic acid on pepper

seedling growth under saline condition. Journal of Environmental Biology, 31(5), pp. 873-

876.

219

Gungula, D.T., Kling, J.G. and Togun, A.O., 2003. Ceres maize predictions of phenology under

nitrogen stressed conditions in Nigeria. Agronomy Journal, 95(4), pp. 892-899.

Gungula, D.T., Togun, A.O. and Kling, J.G., 2007. The effect of nitrogen rates on phenology and

yield components of early maturing maize cultivars. Global Journal of Pure and Applied

Sciences, 13(3), pp. 319-324.

Guo, H., Li, G., Zhang, D. and Zhang, X., 2006. Effects of water table and fertilization

management on nitrogen loading to groundwater. Agricultural Water Management, 82(1),

pp. 86-98.

Habib, M.D., Asif, M., Aziz, M., Ali, A., Ashraf, M., Mahmood, A. and Javaid, M.M., 2016.

Growth performance of spring maize and soil fertility status as influenced by nutrient

sources. International Journal of Agriculture and Applied Sciences, 4(1), pp. 35-41.

Hafidi, M., Amir, S., Meddich, A., Jouraiphy, A., Winterton, P., El Gharous, M. and Duponnois,

R., 2012. Impact of applying composted biosolids on wheat growth and yield parameters

on a calcimagnesic soil in a semi-arid region. African Journal of Biotechnology, 11(41),

pp. 9805-9815.

Hageman, R.H. and Below, F.E., 1984. The role of nitrogen in the productivity of corn. In Report

of Annual Corn and Sorghum Research Conference (USA).

Haghighi, S., Saki-Nejad, T. and Lack, S.H., 2011. Evaluation of changes the qualitative &

quantitative yield of horse been (Vicia faba L.) plants in the levels of humic acid

fertilizer. Life Science Journal, 8(3), pp. 583-588.

Halvorson, A.D., Wienhold, B.J. and Black, A.L., 2001. Tillage, nitrogen and cropping system

effects on soil carbon sequestration. Soil Science Society of America Journal, 66(3), pp.

906-912.

Hamayun, M., Khan, S.A., Khan, A.L., Shinwari, Z.K., Ahmad, N., Kim, Y.H. and Lee, I.J., 2011.

Effect of foliar and soil application of nitrogen, phosphorus and potassium on yield

components of lentil. Pakistan Journal of Botany, 43(1), pp. 391-396.

Hammad, H.M., Ahmad, A., Farhad, W., Abbas, F., Qasim, K. and Saeed, S., 2013. Nitrogen

stimulates phenological traits, growth and growing degree days of maize. Pakistan

Journal of Agricultural Sciences, 50(3), pp. 337-344.

220

Hammad, H.M., Ahmad, A., Khaliq, T., Farhad, W. and Mubeen, M., 2011. Optimizing rate of

nitrogen application for higher yield and quality in maize under semiarid environment.

Crop and Environment, 2(1), pp. 38-41.

Hammad, H.M., Khaliq, A., Ahmad, A., Aslam, M., Malik, A.H., Farhad, W. and Laghari, K.Q.,

2011. Influence of different organic manures on wheat productivity. International Journal

of Agriculture and Biology, 13(1), pp. 137-140.

Hanafi, M.M. and Salwa, H., 1998. Influence of humic acid addition on soil properties and their

adsorption. Communications in Soil Science and Plant Analysis, 29(11-14), pp. 1933-

1947.

Haque, I. and Jakhro, A.A., 1996. Soil and fertilizer nitrogen. Soil Science. Bashir, E. and R.

Bantel (Eds). National Book Foundation, Islamabad, Pakistan, pp. 261-284.

Haque, M.M., Hamid, A. and Bhuiyan, N.I., 2001. Nutrient uptake and productivity as affected

by nitrogen and potassium application levels in maize/sweet potato intercropping system.

Korean Journal of Crop Science, 46(1), pp. 1-5.

Hati, K.M., Swarup, A., Dwivedi, A.K., Misra, A.K. and Bandyopadhyay, K.K., 2007. Changes

in soil physical properties and organic carbon status at the topsoil horizon of a vertisol of

central India after 28 years of continuous cropping, fertilization and manuring.

Agriculture, Ecosytems and Environment, 119(1-2), pp. 127-134.

Havlin, J.L., Beaton, J.D., Tisdale, S.L. and Nelson, W.L., 2005. Soil Fertility and Fertilizers: An

Introduction to Nutrient Management (Vol. 515, pp. 97-141). Upper Saddle River, NJ:

Pearson Prentice Hall.

Hofrichter, M., 2002. lignin conversion by manganese peroxidase (MnP). Enzyme and

Microbial Technology, 30(4), pp. 454-466.

Hopkins, D.W. and Gregorich, E.G., 2005. Carbon as a substrate for soil organisms. Biological

Diversity and Function in Soils, pp. 57-82.

Horst, W.J., Behrens, T., Heuberger, H., Kamh, M., Reidenbach, G. and Wiesler, F., 2003.

Genotypic differences in nitrogen use-efficiency in crop plants. Innovative Soil-Plant

Systems for Sustainable Agricultural Production, 51, pp. 75-92.

Hua, Q.X., Li, J.Y., Zhou, J.M., Wang, H.Y., Du, C.W. and Chen, X.Q., 2008. Enhancement of

phosphorus solubility by humic substances in ferrosols. Pedosphere, 18(4), pp. 533-538.

221

Humintech., 2012. Is it possible to replace humus with organic manure? Available:

http://www.humintech.com/001/industry/information/faq.html.

Hussaini, M.A., Ogunlela, V.B., Ramalan, A.A. and Falaki, A.M., 2001. Growth and development

of maize ( Zea mays L.) in response to different levels of nitrogen, phosphorus and

irrigation. Crop Research, 22(2), pp. 141-149.

Inamullah, Rehman, N., Shah, N.H., Arif, M., Siddiq, M. and Mian, I.A., 2011. Correlations

among grain yield and yield attributes in maize hybrids at various nitrogen levels. Sarhad


Iqbal, B., 2016. Response of wheat crop to humic acid and nitrogen levels. EC Agriculture, 3,

pp. 558-565.

Iqbal, J., Hayat, K. and Hussain, S. Ali. A. and Bakhsh, A., 2012. Effect of seeding rates and

nitrogen levels on yield and yield components of wheat (Triticum aestivum L.). Pakistan

Journal of Nutrition, 11(7), pp. 531-536.

Iqbal, M., Khan, A.G., Hassan, A., Raza, M.W. and Amjad, M., 2012. Soil organic carbon, nitrate

contents, physical properties and maize growth as influenced by dairy manure and

nitrogen rates. International Journal of Agriculture and Biology, 14(1), pp. 20-28.

Iqbal, M., Khan, A.G., Mukhtar, R. and Hussain, S., 2014. Tillage and nitrogen fertilization effect

on wheat yield, and soil organic carbon and total nitrogen. Jounal of Sustainable

Watershed Science Management, 2(1), pp. 108-117.

Iqbal, M.M., Akhter, J., Mohammad, W., Shah, S.M., Nawaz, H. and Mahmood, K., 2005. Effect

of tillage and fertilizer levels on wheat yield, nitrogen uptake and their correlation with

carbon isotope discrimination under rainfed conditions in north-west Pakistan. Soil and

Tillage Research, 80(1-2), pp. 47-57.

Jack, G., 2010. Pivot irrigation create healthy crops and conserve water, too.

http://EzineArticles.com/?expert=Jack_Griffith.

Jan, A., Aslam, K.I., Akber, H. and Khan, G.D., 2007. Yield potential of maize hybrids under

intensive inputs managements. Sarhad Journal of Agriculture, 23(1), pp. 31-34.

Jan, M.T., Hollington, P.A., Khan, M.J. and Sohail, Q., 2009. Agriculture Research: Design and

Analysis, Deptt. of Agronomy, KP Agri. Univ. Peshawar, Pakistan.

222

Jasemi, M., Darabi, F., Naseri, R., Naserirad, H. and Bazdar, S., 2013. Effect of planting date and

nitrogen fertilizer application on grain yield and yield components in maize (SC 704).

American-Eurasian Journal of Agriculture and Environmental Sciences, 13(7): 914-919.

Jassal, R.K., Kang, J.S., Singh, H. and Singh, T., 2017. Growth, phenology and seed yield of

fodder maize in relation to different planting methods and nitrogen levels. International

Journal of Current Microbiology and Applied Sciences, 6(4), pp. 1723-1735.

Javed, H.I., Masood, M.A., Chughtai, S.R., Malik, H.N., Hussain, M. and Saleem, A., 2006.

Performance of maize genotypes on the basis of stability analysis in Pakistan. Asian

Journal of Plant Sciences, 5(2), pp. 207-210.

Jayaganesh, S. and Senthurpandian, V.K., 2010. Extraction and characterization of humic and

fulvic acids from latosols under tea cultivation in South India. Asian Journal of Earth

Sciences, 3(3), pp. 130-135.

Jena, N., Vani, K.P., Rao, V.P. and Sankar, A.S., 2015. Effect of nitrogen and phosphorus

fertilizers on growth and yield of quality protein maize (QPM). International Journal of

Science and Research, 4(8), pp. 1839-1840.

Jilani, G., Akram, A., Ali, R.M., Hafeez, F.Y., Shamsi, I.H., Chaudhry, A.N. and Chaudhry, A.G.,

2007. Enhancing crop growth, nutrients availability, economics and beneficial rhizosphere

microflora through organic and biofertilizers. Annals of Microbiology, 57(2), pp. 177-183.

Jokela, W.E. and Randall, G.W., 1989. Corn yield and residual soil nitrate as affected by time

and rate of nitrogen application. Agronomy Journal, 81(5), pp. 720-726.

Jones, D.L., Rousk, J., Edwards-jones, G., Deluca, T.H. and Murphy, D., 2012. Biochar-mediated

changes in soil quality and plant growth in a three year field trial. Soil Biology and

Biochemistry, 45, pp. 113-124.

Jones, R.J., Schreiber, B. and Roessler, J.A., 1996. Kernel sink capacity in maize: genotypic and

maternal regulation. Crop Science, 36(2), pp. 301-306.

Ju, X.T., Kou, C.L., Christie, P., Dou, Z.X. and Zhang, F.S., 2007. Changes in the soil

environment from excessive application of fertilizers and manures to two contrasting

intensive cropping systems on the North China Plain. Environmental Pollution, 145(2),

pp. 497-506.

Kang, B.T., 1981. Nutrient requirement and fertilizer use for maize. Agronomy Training

Manual for Agroservice Agronomist NAFPP/IITA. Fed. Dept. Agr. Lagos, pp. 405-416.

223

Karakurt, Y., Unlu, H., Unlu, H. and Padem, H., 2009. The influence of foliar and soil fertilization

of humic acid on yield and quality of pepper. Acta Agriculturae Scandinavica, 59(3), pp.

233-237.

Karasu, A., 2012. Effect of nitrogen levels on grain yield and some attributes of some hybrid

maize cultivars (Zea mays L.) grown for silage as second crop. Balgarian Journal of

Agricultural Science, 18(1), pp. 42-48.

Khaled, H. and Fawy, H.A., 2011. Effect of different levels of humic acids on the nutrient content,

plant growth, and soil properties under conditions of salinity. Soil and Water Research,

6(1), pp. 21-29.

Khalil, I.H., Carver, B.F., Krenzer, E.G., MacKown, C.T. and Horn, G.W., 2002a. Genetic trends

in winter wheat yield and test weight under dual-purpose and grain-only management

systems. Crop Science, 42, pp. 710-715.

Khan, A., 2016. Maize (Zea mays L.) genotypes differ in phenology, seed weight and quality

(protein and oil contents) when applied with variable rates and source of nitrogen. Journal

of Plant Biochemistry and Physiology, 4(1), pp. 1-7.

Khan, A., Jan, A., Bashir, S. and Noor, M., 2005. Effect of nitrogen and seed size on maize crop.

I: Stand and plant height. Journal of Agriculture and Social Sciences, 1(4), pp. 380-381.

Khan, A., Khan, R.U., Khan, M.Z., Hussain, F. and Akhtar, M.E., 2013. Characterization and

effects of plant derived humic acid on the growth of Pepper under glasshouse conditions.

Pakistan Journal of Chemistry, 3(3), pp. 134-139.

Khan, A., Gurmani, A.R., Khan, M.Z., Hussain, F., Akhtar, M.E. and Khan, S., 2012. Effect of

humic acid on the growth, yield, nutrient composition, photosynthetic pigment and total

sugar contents of peas (Pisum sativum L.). Journal of the Chemical Society of Pakistan,

1, pp. 1-7.

Khan, A., Sarfraz, M., Ahmad, N. and Ahmad, B., 1994. Effect of nitrogen dose and irrigation

depth on nitrate movement in soil and N uptake by maize. Journal of Agricultural

Research (Pakistan).

Khan, F., Khan, S., Fahad, S., Faisal, S., Hussain, S., Ali, S. and Ali, A., 2014. Effect of different

levels of nitrogen and phosphorus on the phenology and yield of maize varieties. American

Journal of Plant Sciences, 5(17), pp. 2582-2590.

224

Khan, H.Z., Iqbal, S., Akbar, N., Saleem, M.F. and Iqbal, A., 2013. Integrated management of

different nitrogen sources for maize production. Pakistan Journal of Agricultural

Sciences, 50(1), pp. 55-61.

Khan, H.Z., Iqbal, S., Iqbal, A., Akbar, N. and Jones, D.L., 2011. Response of maize (Zea mays

L.) varieties to different levels of nitrogen. Crop and Environment, 2(2), pp. 15-19.

Khan, M.A., Akbar, S., Ahmad, K. and Baloch, M.S., 1999. Evaluation of corn hybrids for grain

yield in D.I. Khan. Pakistan Journal of Biological Sciences, 2(2), pp. 413-414.

Khan, M.A.H. and Parvej, M.R., 2011. Impact of conservation tillage under organic mulches on

the reproductive efficacy and yield of quality protein maize. Journal of Agricultural

Sciences, 5(2), pp. 52-63.

Khan, M.I. and Jan, A., 2017. Maize response to soil conditioning and irrigation regimes.

International Journal of Biosciences, 11(6), pp. 100-115.

Khan, M.Z., Akhtar, M.E., Ahmad, S., Khan, A. and Khan, R.U., 2014. Chemical composition of

lignitic humic acid and evaluating its positive impacts on nutrient uptake, growth and yield

of maize. Pakistan Journal of Chemistry, 4(1), pp. 19-25.

Khan, R.U., Rashid, A., Khan, M.S. and Ozturk, E., 2010. Impact of humic acid and chemical

fertilizer application on growth and yield of rainfed wheat (Triticum aestivum L.).

Pakistan Journal of Agricultural Research, 23(3-4), pp. 113-121.

Khattak, M.K., 2004. Influence of various tillage practices on yield of wheat-maize under clay

loam soil condition. Sarhad Journal of Agriculture, 20, pp. 429-443.

Khattak, R.A. and Muhammad, D., 2013. Mechanism (s) of humic acid induced beneficial effects

in salt-affected soils. Scientific Research and Essays, 8(21), pp. 932-939.

Kim, Y.H., Khan, A.L., Shinwari, Z.K., Kim, D.H., Waqas, M., Kamran, M. and Lee, I.J., 2012.

Silicon treatment to rice (Oryza sativa L. cv ‘Gopumbyeo’) plants during different growth

periods and its effects on growth and grain yield. Pakistan Journal of Botany, 44(3), pp.

891-897.

Koester, R.P., Skoneczka, J.A., Cary, T.R., Diers, B.W. and Ainsworth, E.A., 2014. Historical

gains in soybean (Glycine max L.) seed yield are driven by linear increases in light

interception, energy conversion, and partitioning efficiencies. Journal of Experimental

Botany, 65(12), pp. 3311-3321.

225

Koochekzadeh, A., Fathi, G., Gharineh, M.H., Siadat, S.A., Jafari, S. and Alami-Saeid, K., 2009.

Impacts of rate and split application of N fertilizers on sugarcane quality. International

Journal of Agricultural Research, 4(3), pp. 116-123.

Kolari, F., Bazregar, A. and Bakhtiari, S., 2014. Phenology, growth aspects and yield of maize

affected by defoliation rate and applying nitrogen and vermicompost. Indian Journal of

Fundamental and Applied Life Sciences, 4(3), pp. 61-71.

Kulikova, N.A., Stepanova, E.V. and Koroleva, O.V., 2005. Mitigating activity of humic

substances: direct influence on biota. In Use of Humic Substances to Remediate Polluted

Environments: From Theory to Practice (pp. 285-309). Springer, Dordrecht.

Kumar, A., Gali, S.K. and Hebsur, N.S., 2010. Effect of different levels of NPK on growth and

yield parameters of sweet corn. Karnataka Journal of Agricultural Sciences, 20(1), pp.

41-43.

Kumar, P., Halepyati, A.S., Pujari, B.T. and Desai, B.K., 2007. Effect of integrated nutrient

management on productivity, nutrient uptake and economics of maize (Zea mays L.) under

rain fed condition. Karnataka Journal of Agricultural Sciences, 20(3), pp. 462-465.

Kumar, S.N. and Singh, C.P., 2001. Growth analysis of maize during long and short duration crop

seasons: influence of nitrogen source and dose. Indian Journal of Agricultural Research,

35(1), pp. 13-18.

Kuşvuran, V.S.A. and Babat, S., 2011. The effect of different humic acid fertilization on yield and

yield components performances of common millet (Panicum miliaceum L.). Scientific

Research and Essays, 6(3), pp. 663-669.

Ladha, J.K., Pathak, H., Krupnik, T.J., Six, J. and van Kessel, C., 2005. Efficiency of fertilizer

nitrogen in cereal production: retrospects and prospects. Advances in Agronomy, 87, pp.

85-156.

Lal, R., 2013. Food security in a changing climate. Ecohydrology and Hydrobiology, 13(1), pp.

8-21.

Lamkey, K.R. and Hallauer, A.R., 1986. Performance of high × high, high × low, and low × low

crosses of lines from the BSSS maize synthetic. Crop Science, 26(6), pp. 1114-1118.

Langade, D.M., Shahi, J.P., Srivastava, K., Singh, A., Agarwal, V.K. and Sharma, A., 2013.

Appraisal of genetic variability and seasonal interaction for yield and quality traits in

maize (Zea mays L.). Plant Gene and Trait, 4(18), pp. 95-103.

226

Lawrence, J.R., Ketterings, Q.M. and Cherney, J.H., 2008. Effect of nitrogen application on yield

and quality of corn. Agronomy Journal, 100(1), pp. 73-79.

Li, H., Han, Y. and Cai, Z., 2003. Nitrogen mineralization in paddy soils of the Taihu region of

China under anaerobic conditions: dynamics and model fitting. Geoderma, 115(3-4), pp.

161-175.

Li, S.Q., Li, S.X. and Li, F.M., 2000. Mineralization and nitrification of soil nitrogen in calcareous

soil profile. Journal of Lanzhou University, 36(1), pp. 98-104.

Li, S.X., Wang, Z.H., Miao, Y.F. and Li, S.Q., 2014. Soil organic nitrogen and its contribution to

crop production. Journal of Integrative Agriculture, 13(10), pp. 2061-2080.

Liang, T.B., Wang, Z.L. , Liu, L.L., Wang, R.J., Chen, X.G., Zhang, X.D. and Shi, C.Y., 2016.

Effects of humic acid urea on yield and nitrogen absorption, assimilation and quality of

ginger. Journal of Plant Nutrition and Fertilizer, 13(5), pp. 903-909.

Liduke, L., 2014. Assessment Of The Nitrogen And Phosphorus Needs And Use Efficiencies

For Enhanced Maize Yields In Mbozi District Of Tanzania (Doctoral dissertation,

Sokoine University of Agriculture).

Limon-Ortega, A., Sayre, K.D. and Francis, C.A., 2000. Wheat nitrogen use efficiency in a bed

planting system in Northwest Mexico. Agronomy Journal, 92(2), pp. 303-308.

Liu, M., Hu, F., Chen, X., Huang, Q., Jiao, J., Zhang, B. and Li, H., 2009. Organic amendments

with reduced chemical fertilizer promote soil microbial development and nutrient

availability in a subtropical paddy field: the influence off quantity, type and application

time of organic amendments. Applied Soil Ecology, 42(2), pp. 166-175.

López-Bellido, R.J. and López-Bellido, L., 2001. Efficiency of nitrogen in wheat under

Mediterranean condition: effect of tillage, crop rotation and N fertilization. Field Crops

Research, 71(1), pp. 31-64.

Lugg, D.G. and Sinclair, T.K., 1979. A survey of soybean cultivars for variability in specific

leaf weight. Crop Science, 19(6), pp. 887-892.

Luque, S.F., Cirilo, A.G. and Otegui, M.E., 2006. Genetic gains in grain yield and related

physiological attributes in Argentine maize hybrids. Field Crops Research, 95(2-3), pp.

383-397.

227

Mackowiak, C.L., Grossl, P.R. and Bugbee, B.G., 2001. Beneficial effects of humic acid on

micronutrient availability to wheat. Soil Science Society of America Journal, 65(6), pp.

1744-1750.

Madani, A., Makarem, A.H., Vazin, F. and Joudi, M., 2012. The impact of post-anthesis nitrogen

and water availability on yield formation of winter wheat. Plant, Soil and Environment,

58(1), pp. 9-14.

Maddonni, G.A. and Otegui, M.E., 2004. Intra-specific competition in maize: Early establishment

of hierarchies among plants affects final kernel set. Field Crops Research, 85(1), pp. 1-

13.

Maddonni, G.A. and Otegui, M.E., 2006. Intra-specific competition in maize: Contribution of

extreme plant hierarchies to grain yield, grain yield components and kernel composition.

Field Crops Research, 97(2-3), pp. 155-166.

Madronová, L., Kozler, J., Čežı́ková, J., Novák, J. and Janoš, P., 2001. Humic acids from coal

of the North-Bohemia coal field: III. Metal-binding properties of humic acids-

measurements in a column arrangement. Reactive and Functional Polymers, 47(2), pp.

119-123.

Majidian, M., Ghalavand, A., Karimian, N. and Haghighi, A.K., 2006. Effects of water stress,

nitrogen fertilizer and organic fertilizer in various farming systems in different growth

stages on physiological characteristics, physical characteristics, quality and chlorophyll

content of maize single cross hybrid 704. Iranian Crop Science Journal, 10(3), pp. 303-

330.

Major, D.J., 1980. Photoperiod response characteristics controlling flowering of nine crop species.

Canadian Journal of Plant Science, 60(3), pp. 777-784.

Malaiya, S., Tripathi, R.S. and Shrivastava, G.K., 2004. Effect of variety, sowing time and

integrated nutrient management on growth, yield attributes and yield of summer maize.

Annals of Agricultural Research, 25(1), pp. 155-158.

Malcolm, R.E. and Vaughan, D., 1979. Humic substances and phosphatase activities in plant

tissues. Soil and Biology Biochemistry, 11(3), pp. 253-259.

Malhi, S.S. and Gill, K.S., 2004. Placement, rate and source of N, seed row opener and seeding

depth effects on canola production. Canadian Journal of Plant Science, 84(3), pp. 719-

729.

228

Malhi, S.S., Gan, Y. and Raney, J.P., 2007. Yield, seed quality, and sulfur uptake of Brassica oil

seed crops in response to sulfur fertilization. Agronomy Journal, 99(2), pp. 570-577.

Malik, H.N., Malik, S.I., Hussain, M., Chughtai, S.R. and Javed, H.I., 2005. Genetic correlation

among various quantitative characters in maize (Zea mays L.) hybrids. Journal of

Agriculture and Social Sciences, 3, pp. 262-265.

Maliwal, P.L., Maliwal, P.L. and Mundra, S.L., 2007. Agronomy At a Glance. Agrotech

Publishing Academy.

Malvi, U.R., 2011. Interaction of micronutrients with major nutrients with special reference to

potassium. Karnataka Journal of Agricultural Sciences, 24(1). pp. 106-109.

Mandal, N.N., Chaudhry, P.P. and Sinha, D., 1992. Nitrogen, phosphorus and potash uptake of

wheat (var. Sonalika). Environment and Ecology, 10, p. 297.

Mansour, A.L., 2009. Response of two maize hybrids to urea fertilization under application of

hydroquinone urease inhibitor. Journal of Agricultural Sciences, 34(5), pp. 4977-4990.

Manzoor, Z., Awan, T.H., Safdar, M.E., Ali, R.I., Ashraf, M.M. and Ahmad, M., 2006. Effect of

nitrogen levels on yield and yield components of Basmati 2000. Journal of Agricultural

Research, 44(2), pp. 115-120.

Marschner, H., 1995. Mineral nutrition of higher plants. 2nd (eds) Academic Press. New York.

Masciandaro, G., Ceccanti, B., Ronchi, V., Benedicto, S. and Howard, L., 2002. Humic substances

to reduce salt effect on plant germination and growth. Communications in Soil Science

and Plant Analysis, 33(3-4), pp. 365-378.

Mauromicale, G., Longo, A.M.G. and Monaco, A.L., 2011. The effect of organic supplementation

of solarized soil on the quality of tomato fruit. Scientia Horticulturae, 129(2), pp. 189-

196.

Mayhew, L., 2004. Humic substances in biological agriculture. Rev ACRES, 34(1-2), pp. 80-88.

McCullough, D.E., Mihajlovic, M., Aguilera, A., Tollenaar, M. and Girardin, P., 1994. Influence

of N supply on development and dry matter accumulation of an old and a new maize

hybrid. Canadian Journal of Plant Science, 74(3), pp. 471-477.

McDonnell, R., Holden, N.M., Ward, S.M., Collins, J.F., Farrell, E.P. and Hayes, M.H.B., 2001,

December. Characteristics of humic substances in heathland and forested peat soils of the

229

Wicklow Mountains. In Biology and Environment: Proceedings of the Royal Irish

Academy (pp. 187-197). Royal Irish Academy.

Mengel, K., Kirkby, E.A., Kosegarten, H. and Appel, T., 2001. Soil Copper. In Principles of Plant

Nutrition (pp. 599-611). Springer, Dordrecht.

Mi, G., Chen, F. and Zhang, F., 2007. Physiological and genetic mechanisms for nitrogen-use

efficiency in maize. Journal of Crop Science and Biotechnology, 10(2), pp. 57-63.

Milford, G.F.J., Pocock, T.O., Riley, J. and Messem, A.B., 1985. An analysis of leaf growth in

sugar beet. Annals of Applied Biology, 106(1), pp. 187-203.

Miller, A.J., Fan, X., Orsel, M., Smith, S.J. and Wells, D.M., 2007. Nitrate transport and

signalling. Journal of Experimental Botany, 58(9), pp. 2297-2306.

Mindari, W., Aini, N., Kusuma, Z. and Syekhfani, S., 2014. Effects of humic acid-based cation

buffer on chemical characteristics of saline soil and growth of maize. Journal of Degraded

and Mining Lands Management, 2(1), pp. 259-268.

Mkhabela, M.S. and Shikhulu, J.P., 2001. Response of maize (Zea mays L.) cultivars to different

levels of nitrogen application in Swaziland during the 1994 cropping season. UNISWA


Moghadam, H.T., Khamene, M.K. and Zahedi, H., 2015. Effect of humic acid foliar application

on growth and quantity of corn in irrigation withholding at different growth stages.

Maydica, 59(2), pp. 124-128.

Mohamed, A.M., 2006. Effect of Some Bio-chemical Fertilization Regimes On Yield Of

Maize (Doctoral dissertation, M.Sc. Thesis, Fac. of Agri., Zagazig Univ., Egypt).

Mohammadpourkhaneghah, A., Shahryari, R., Alaei, Y. and Shahmoradmoghanlou, B., 2012.

Comparison of the effect of liquid humic fertilizers on yield of maize genotypes in Ardabil

region. African Journal of Biotechnology, 11(21), pp. 4810-4814.

Mohana, A.A., Suleiman, M.M. and Khedr, W.S., 2015. Effect of humic acid and rates of nitrogen

fertilizer on yield and yield components of corn (Zea mays L.). Jordan Journal of


Mohd, T., Osumanu, H.A. and Nik, M., 2009. Effect of mixing urea with humic acid and acid

sulphate soil on ammonia loss, exchangeable ammonium and available nitrate. American

Journal of Environmental Sciences, 5(5), pp. 588-591.

230

Mohsan, S., 1999. Population Dynamics And Nitrogen Management Effects On Maize

Productivity (Doctoral dissertation, Univ. of Agri. Faisalabad).

Moll, R.H., Kamprath, E.J. and Jackson, W.A., 1982. Analysis and interpretation of factors which

contribute to efficiency of nitrogen utilization. Agronomy Journal, 74(3), pp. 562-564.

Moller, K. and Reents, H.J., 2009. Effects of various cover crops after peas on nitrate leaching

and nitrogen supply to succeeding winter wheat or potato crops. Journal of Plant Nutrition

and Soil Science, 172(2), pp. 277-287.

Moznur Rahman, M., Raihan Ali, M., Sirajul Islam, M., Khaled Sultan, M. and Mitra, B., 1995.

Correlation and path coefficient studies in maize (Zea mays L.) composites. Bangladesh

Journal of Scientific and Industrial Research, 30, pp. 87-92.

Moraditochaee, M., 2012. Effects of humic acid foliar spraying and nitrogen fertilizer

management on yield of peanut (Arachis hypogaea L.) in Iran. ARPN Journal of

Agricultural and Biological Science, 7(4), pp. 289-293.

Morard, P., Eyheraguibel, B., Morard, M. and Silvestre, J., 2011. Direct effects of humic like

substance on growth, water, and mineral nutrition of various species. Journal of Plant

Nutrition, 34(1), pp. 46-59.

Mosely, E.I. and Zahran, M.A., 2002. Effect of bio and mineral nitrogen fertilization on barley

crop grown on a sandy soil. Egyptian Journal of Agricultural Research, 3, 921-936.

Motaghi, S. and Nejad, T.S., 2014. The effect of different levels of humic acid and potassium

fertilizer on physiological indices of growth. International Journal of Biosciences, 5(2),

pp. 99-105.

Moussa, B.I.M. and Barsoum, M.S., 1995. The mutual effect of sulphur and magnesium under Zn

application on maize at South Tahreer Province. Annals of Agricultural Sciences,

Moshtohor (Egypt), 33(3), pp. 1035-1050.

Muchow, R.C. and Davis, R., 1988. Effect of nitrogen supply on the comparative productivity of

maize and sorghum in a semi-arid tropical environment. II. Radiation interception and

biomass accumulation. Field Crops Research, 18(1), pp. 17-30.

Munawar, M., Hammad, G. and Shahbaz, M., 2013. Evaluation of maize (Zea mays L.) hybrids

under different environments by GGE biplot analysis. American-Eurasian Journal of

Agricultural and Environmental Sciences, 13(9), pp. 1252-1257.

231

Muzilli, O., Oliveira, E.L. and Adubação, N.E., 1992. In: Instituto Agronômico Do Paraná (P.R.

Londrina). O milho no Paraná. Londrina, Pp. 88-95.

Nardi, S., Concheri, G. and Dell’Agnola, G., 1996. Biological activity of humus. In Humic

Substances in Terrestrial Ecosystems. Elsevier, Amsterdam (pp. 361-406).

Nardi, S., Pizzeghello, D., Muscolo, A. and Vianello, A., 2002. Physiological effects of humic

substances on higher plants. Soil Biology and Biochemistry, 34(11), pp. 1527-1536.

Nardi, S., Sessi, E., Pizzeghello, D., Sturaro, A., Rella, R. and Parvoli, G., 2002. Biological

activity of soil organic matter mobilized by root exudates. Chemosphere, 46(7), pp.

1075-1081.

Ndakidemi, P. and Dakora, F.D., 2007. Yield components of nodulated cowpea (Vigna

unguiculata L.) and maize (Zea mays L.) plants grown with exogenous phosphorus in

different cropping systems. Australian Journal of Experimental Agriculture, 47(5), pp.

583-589.

Nelson, D.W. and Sommers, L., 1982. Total carbon, organic carbon, and organic matter. In

Methods of Soil Analysis. Part 2. Chemical and Microbiological Properties, (pp. 539-

579).

Niaz, A., Yaseen, M., Arshad, M. and Ahmad, R., 2015. Response of maize yield, quality and

nitrogen use efficiency indices to different rates of N and application timings. Journal of

Animal and Plant Sciences, 25(4), pp. 1022-1031.

Niaz, A., Yaseen, M., Shakar, M., Sultana, S., Ehsan, M. and Nazarat, A., 2016. Maize production

and nitrogen use efficiency in response to nitrogen application with and without humic

acid. Journal of Animal and Plant Sciences, 26(6), pp. 1641-1651.

Nisar, A. and Mir, S., 1989. Lignitic coal utilization in the form of humic acids as fertilizer and

soil conditioner. Science, Technology and Development, 8(1), pp. 23-26.

Nithila, S., Annadurai, K., Jeyakumar, P., Puppala, N. and Angadi, S., 2013. Humic acid on

growth, yield and biochemical properties of field crops with particular reference to peanut:

A Review. American International Journal of Research in Science, Technology,

Engineering and Mathematics, 4(2), pp. 128-132.

Nofal, F.A., Soliman, M.S.M. and Abdel-Ghani, M.M., 2005. Effect of irrigation at different water

depletions levels, nitrogen, and manure applications on water use efficiency and maize

grain yield in sandy soils. Minify Journal of Agricultural Research, 30(4), pp. 1159-1177.

232

Nord, E.A. and Lynch, J.P., 2009. Plant phenology: a critical controller of soil resource

acquisition. Journal of Experimental Botany, 60(7), pp. 1927-1937.

Nyamangara, J., Piha, M.I. and Giller, K.E., 2003. Effect of combined cattle manure and mineral

nitrogen on maize nutrient uptake and grain yield. African Crop Science Journal, 11(4),

pp. 289-300.

Oad, F.C., Buriro, U.A. and Agha, S.K., 2004. Effect of organic and inorganic fertilizer

application on maize fodder production. Asian Journal of Plant Sciences, 3, pp. 375-377.

Obi, M.E. and Ebo, P.O., 1995. The effect of organic and inorganic amendments on soil physical

properties and maize production in a several degraded sandy soils. Bioresource

Technology, 51(2-3), pp. 117-123.

Ogola, J.B.O., Wheeler, T.R. and Harris, P.M., 2002. Effects of nitrogen and irrigation on water

use of maize crops. Field Crops Research, 78(2-3), pp. 105-117.

Oikeh, S.O., Kling, J.K., Horst, W. and Chude, V.O., 1997. Yield and N-Use efficiency of five

tropical maize genotypes under different N levels in the moist savanna of Nigeria.

In Proceedings of The Fifth Eastern and Southern Africa Regional Maize Conference,

Ddis Ababa: CIMMYT (pp. 163-167).

Ojeniyil, S.O. and Kayode, G.O., 1993. Response of maize to copper and sulphur in tropical

regions. Journal of Agricultural Sciences, 120(3), pp. 295-299.

Onasanya, R.O., Aiyelari, O.P., Onasanya, A., Oikeh, S., Nwilene, F.E. and Oyelakin, O.O., 2009.

Growth and yield response of maize (Zea mays L.) to different rates of nitrogen and

phosphorus fertilizers in southern Nigeria. World Journal of Agricultural Sciences, 5(4),

pp. 400-407.

Ortiz-Monasterio, J.I., Sayre, K.D., Rajaram, S. and McMahon, M., 1997. Genetic progress in

wheat yield and nitrogen use efficiency under four nitrogen rates. Crop Science, 37(3), pp.

898-904.

Otegui, M.E., 1995. Prolificacy and grain yield components in modern Argentinian maize hybrids.

Maydica, 40, pp. 371-376.

ÖZ, A., 2012. Comparison of hybrid maize obtained from inbred lines that are selected via top-

crossing and discriminant analysis. Turkish Journal of Agriculture and Forestry, 36(6),

pp. 659-667.

233

Ozkutlu, F., Torun, B. and Cakmak, I., 2006. Effect of zinc humate on growth of soybean and

wheat in zinc-deficient calcareous soil. Communications in Soil Science and Plant

Analysis, 37(15-20), pp. 2769-2778.

Page, A.L., Miller, R.H. and Keeney, D.R., 1982. Methods of soil analysis. Part 2. Chemical

and microbiological properties. Agronomy, No. 9. Soil Science Society of America,

Madison, WI, p. 1159.

Pakistan Economic Survey., 2014. Pakistan Bureau of Statistics, p. 29.

Paponov, I.A., Sambo, P., Presterl, T., Geiger, H.H. and Engels, C., 2005. Grain yield and kernel

weight of two maize genotypes differing in nitrogen use efficiency at various levels of

nitrogen and carbohydrate availability during flowering and grain filling. Plant and

Soil, 272(1-2), pp. 111-123.

Paradkar, V.K. and Sharma, R.K., 1993. Effect of nitrogen fertilization on maize (Zea mays L.)

varieties under rainfed condition. Indian Journal of Agronomy, 38(2), pp. 303-304.

Pettit, R.E., 2004. Organic matter, humus, humate, humic acid, fulvic acid and humin: their

importance in soil fertility and plant health. CTI Research.

Pikul, J.L., Hammack, L. and Riedell, W.E., 2005. Corn yield, nitrogen use and corn rootworm

infestation of rotations in the northern corn belt. Agronomy Journal, 97, pp. 854-863.

Pollhamer, Z., 1993. Effect of humic acid, fulvic acid and NPK fertilizers on the quality of winter

wheat varieties on chemical free soil in Hungarian. Növénytermelés, 42(5), pp. 447-455.

Popescu, G.C. and Popescu, M., 2018. Yield, berry quality and physiological response of

grapevine to foliar humic acid application. Bragantia, 77 (2), pp. 273-282.

Prado, S.A., Gambín, B.L., Novoa, A.D., Foster D., Senior, M.L., Zinselmeier, C., Otegui, M.E.

and Borrás, L., 2013. Correlation between parental inbred lines and derived hybrid

performance for grain filling traits in maize. Crop Science, 53(4), pp. 1636-1645.

Prado, S.A., López, C.G., Senior, M.L. and Borrás, L., 2014. The genetic architecture of maize

(Zea mays L.) kernel weight determination. G3: Genes, Genomes, Genetics, 4(9), pp.

1611-1621.

Prodhan, A.A.U.D., 1999. Effect of water stresses on the growth features of different maize (Zea

mays L.) cultivars. Pakistan Journal of Botany, 31(2), pp. 455-460.

234

Prodhan, H.S. and Rai, R., 1997. Genetic variability in popcorn. Indian Agriculture, 41(4), pp.287-

290.

Puglisi, E., Fragoulis, G., Ricciuti, P., Cappa, F., Spaccini, R., Piccolo, A., Trevisan, M. and

Crecchio, C., 2009. Effect of a humic acid and its size-fractions on the bacterial

community of soil rhizosphere under maize (Zea mays L.). Chemosphere, 77(6), pp. 829-

837.

Qadoons, M., Suleman, M., Khan, H., Aqeel, M. and Rafiq, M., 2015. Response of maize crop to

different levels of humic acid. Life Sciences International Journal, 9(1, 2, 3 & 4), pp.

3116-3120.

Qamar M., Gurmani, Z.A., Malik, H.N. and Tanveer, S.K., 2007. Evaluation of maize

hybrids/synthetics under double cropping zone of Northern areas of Pakistan. Sarhad


Quaggiotti, S., Ruperti, B., Pizzeghello, D., Francioso, O., Tugnoli, V. and Nardi, S., 2004. Effect

of low molecular size humic substances on nitrate uptake and expression of genes involved

in nitrate transport in maize (Zea mays L.). Journal of Experimental Botany, 55(398), pp.

803-813.

Radford, P.J., 1967. Growth analysis formulae; their use and abuse. Crop Science, 7(3), pp. 171-

175.

Rafiq, M.A., Ali, A., Malik, M.A. and Hussain, M., 2010. Effect of fertilizer levels and plant

densities on yield and protein contents of autumn planted maize. Pakistan Journal of


Rahimizadeh, M., Zare-Feizabadi, A. and Koocheki, A., 2013. Winter wheat growth response

to preceding crop, nitrogen fertilizer rate and crop residue. International Journal of


Rahmati, H., 2009. Effect of plant density and nitrogen rates on yield and nitrogen use efficiency

of grain corn. World Applied Sciences Journal, 7(8), pp. 958-961.

Rahmati, H., 2012. Effect of plant density and nitrogen rates on morphological characteristics of

grain maize. Journal of Basic and Applied Scientific Research, 2(5), pp. 4680-4683.

Rajpar, I., Bhatti, M.B., Zia-ul-Hassan, Shah, A.N. and Tunio, S.D., 2011. Humic acid

improves growth, yield and oil content of Brassica compestris L. Pakistan Journal of

Agriculture, Agricultural Engineering and Veterinary Sciences, 27(2), pp. 125-133.

235

Ramírez, A.A., Martín-Benito, J.M.T., de Juan Valero, J.A., Álvarez, J.F.O. and Maturano, M.,

2005. Growth and nitrogen use efficiency of irrigated maize in a semiarid region as

affected by nitrogen fertilization. Spanish Journal of Agricultural Research, 1, pp. 134-

144.

Rashid, A. and Ahmad, N., 1993, August. Soil testing in Pakistan: country report.

In Proceedings of the FADINAP Regional Workshop on Cooperation in Soil Testing

for Asia and The Pacific (pp. 16-18).

Rassam, G., Dadkhah, A., Yazdi, A.K. and Dashti, M., 2015. Impact of humic acid on yield

and quality of sugar beet (Beta vulgaris L.) grown on calcareous soils. Notulae Scientia

Biologicae, 7(3), pp. 367-371

Raun, W.R. and Johnson, G.V., 1999. Improving nitrogen use efficiency for cereal production.

Agronomy Journal, 91(3), pp. 357-363.

Reddy, K.R., Feijtel, T.C. and Patrick Jr, W.H., 1986. Effect of soil redox conditions on microbial

oxidation of organic matter. In The Role of Organic Matter in Modern Agriculture (pp.

117-156). Springer, Dordrecht.

Reddy, S.R., 2004. Principles of crop production. Growth regulators and growth analysis, 2nd Ed.

Kalyani publishers, Ludhiana, India.

Reddy, V.M. and Daynard, T.B., 1983. Endosperm characteristics associated with rate of grain

filling and kernel size in corn. Maydica, 28, pp. 339-355.

Reich, P.B., Walters, M.B. and Ellsworth, D.S., 1997. From tropics to tundra: global convergence

in plant functioning. Proceedings of the National Academy of Sciences, 94(25), pp. 13730-

13734.

Rezazadeh, H., Khorasani, S.K. and Haghighi, R.S.A., 2012. Effects of humic acid on decrease of

phosphorus usage in forage maize var. KSC704 (Zea mays L.). Australian Journal of

Agricultural Engineering, 3(2), pp. 34-38.

Rezvantalab, N., Pirdashti, H., Bahmanyar, M.A. and Abasian, A., 1998. Evaluating effects of

municipal waste compost and chemical fertilizer application on yield and yield

components of maize (Zea mays L.). Journal of Agricultural Sciences and Natural

Resources, 5(1), pp. 15-25.

Rijpma, J. and Jahiruddin, M., 2004. National Strategy and Plan for Use of Soil Nutrient Balance

in Bangladesh. A Consultancy Report, SFFP, Khamarbari, Dhaka, pp. 7-26.

236

Rizwan, M., Maqsood, M., Rafiq, M., Saeed, M. and Ali, Z., 2003. Maize (Zea mays L.) response

to split application of nitrogen. International Journal of Agriculture and Biology, 5(1), pp.

19-21.

Robinson, D., 2001. Root proliferation, nitrate inflow and their carbon costs during nitrogen

capture by competing plants in patchy soil. Plant and Soil, 232(1-2), pp. 41-50.

Rodrigues, L.A., Alves, C.Z., Rego, C.H.Q., Silva, T.R.B.D. and Silva, J.B.D., 2017. Humic acid

on germination and vigor of corn seeds. Revista Caatinga, 30(1), pp. 149-154.

Rondanini, D.P., Savin, R. and Hall, A.J., 2007. Estimation of physiological maturity in sunflower

as a function of fruit water concentration. European Journal of Agronomy, 26(3), pp. 295-

309.

Rosecrance, R.C., McCarty, G.W., Shelton, D.R. and Teasdale, J.R., 2000. Denitrification and N

mineralization from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) cover crop

monocultures and bicultures. Plant and Soil, 227(1), pp. 283-290.

Sabata, R.J. and Mason, S.C., 1992. Corn hybrid interactions with soil nitrogen level and water

regime. Journal of Production Agriculture, 5(1), pp. 137-142.

Saber, M.S.M. and Zanati, M.R., 1984. Effectiveness of inoculation with silicate bacteria in

relation to the potassium content of plants [corn] using the intensive cropping technique

[Egypt]. Agricultural Research Review, Cairo.

Sabir, M.R., Ahmad, I. and Shahzad, M.A., 2000. Effect of nitrogen and phosphorus on yield and

quality of two hybrids of maize (Zea mays L.). Journal of Agricultural Research, 38(4),

pp. 339-346.

Sachs, M.M. and Ho, T.H.D., 1986. Alteration of gene expression during environmental stress in

plants. Annual Review of Plant Physiology, 37(1), pp. 363-376.

Sadiq, S.A., Baloch, D.M., Ahmed, N. and Hidayatullah., 2014. Role of coal-derived humic acid

in the availability of nutrients and growth of sunflower under calcareous soil. Journal of

Animal and Plant Sciences, 24(6), pp. 1737-1742.

Sadras, V.O., 2007. Evolutionary aspects of the trade-off between seed size and number in crops.

Field Crops Research, 100(2-3), pp. 125-138.

237

Sahrawat, K.L. and Narteh, L.T., 2003. A chemical index for predicting ammonium production

in submerged rice soils. Communications in Soil Science and Plant Analysis, 34(7-8), pp.

1013-1021.

Sajid, M., Rab, A., Shah, S.T., Jan, I., Haq, I., Haleema, B., Zamin, M., Alam, R. and Zada, H.,

2012. Humic acids affect the bulb production of onion cultivars. African Journal of

Microbiology Research, 6(28), pp. 5769-5776.

Saleem, A., Haqqani, A.M., Javed, H.I., Ali, Z. and Fateh, J., 2006. Economical level of NP-

fertilizer for growing maize crop in Pakistan. International Journal of Agriculture and

Biology, 8(4), pp. 567-568.

Saleem, R., 2010. Economic Feasibility Of Integrated Nutrient Management For Sustainable

Rainfed Maize-Legume Based Intercropping Systems (Doctoral dissertation, PMAS-Arid

Agriculture University, Rawalpindi).

Salman, S.R., Abou-Hussein, S.D., Abdel-Mawgoud, A.M.R. and El-Nemr, M.A., 2005. Fruit

yield and quality of watermelon as affected by hybrids and humic acid application. Journal

of Applied Sciences Research, 1(1), pp. 51-58.

Sani, B. and Jodaeian, V., 2017. Evaluation of humic acid effect on essential oil yield in yarrow

medicinal plant by view of approaches in sustainable agriculture. Journal of Agroecology

and Natural Resource Management, 4(5), pp. 383-387.

Sánchez-Monedero, M.A., Mondini, C., De Nobili, M., Leita, L. and Roig, A., 2004. Land

application of biosolids. Soil response to different stabilization degree of the treated

organic matter. Waste Management, 24(4), pp. 325-332.

Sanjeev, K., Bangarwa, A.S. and Kumar, S., 1997. Yield and yield components of winter maize

(Zea mays L.) as influenced by plant density and nitrogen levels. Agricultural Science

Digest, 17, pp. 181-184.

Santa Bahadur, B.K. and Shrestha, J., 2014. Effect of conservation agriculture on growth and

productivity of maize (Zea mays L.) in Terai region of Nepal. World Journal of


Sarir, M.S., Akhlaq, M., Zeb, A. and Sharif, M., 2005. Comparison of various organic manures

with or without chemical fertilizers on the yield and components of maize. Sarhad Journal

of Agriculture, 21(2), pp. 237-245.

238

Sarma, B., Gogoi, N., Paul, S. and Baroowa, B., 2013. Impact of inorganic N fertilizer on soil

organic carbon and physico-chemical properties of Alluvial Soil of Assam. International

Journal of Agriculture and Food Science Technology, 4(8), pp. 743-744.

Sarwar, M., Akhtar, M.E., Hyder, S.I. and Khan, M.Z., 2012. Effect of biostimulant (humic acid)

on yield, phosphorus, potassium and boron use efficiency in peas. Persian Gulf Crop

Protection, 1(4), pp. 11-16.

Sathiyabhama, K., Selvakumari, G., Santhi, R. and Singaram, P., 2003. Effect of humic acid on

nutrient release pattern in an Alfisol (Typic Haplustalf). Madras Agricultural

Journal, 90(10-12), pp. 665-670.

Schofield, P., Watt, N. and Schofield, M., 2012. Using humic compounds to improve efficiency

of fertiliser nitrogen. School Biol. Sci., Victoria Uni., Wellington. Pp. 1-7.

Schrader, L.E., 1984. Function and transformations of nitrogen in higher plants. Nitrogen in Crop

Production, pp. 55-65.

Scott, R.K. and Jaggard, K.W., 1978. Theoretical criteria for maximum yield. In Proceedings

of the 41st Winter Congress of the International Institute for Sugar Beet Research (pp.

179-198).

Sebetha, E.T., Modi, A.T. and Owoeye, L.G., 2015. Maize seed quality in response to different

management practices and sites. Journal of Agricultural Science, 7(1), pp. 215-223.

Selim, E.M., El-Neklawy, A.S. and El-Ashry, S.M., 2010. Beneficial effects of humic

substances on soil fertility to fertigated potato grown on sandy soil. Libyan Agriculture

Research Center Journal International, 1(4), pp. 255-262.

Selim, E.M., Mosa, A.A. and El-Ghamry, A.M., 2009. Evaluation of humic substances

fertigation through surface and subsusrface drip irrigation systems on potato grown

under Egyptian sandy soil conditions. Agricultural Water Management, 96(8), pp.

1218-1222.

Seyedbagheri, M.M., 2008, September. A Perspective on over a decade of on-farm research on

the influence of humates products on crop production. In Proeedings of the 14th

Meeting of International Humic Substances Society. From Molecular Understanding

to Innovative Applications of Humic Substances. IV Perminova and NA

Kulikova.(eds) (Vol. 2008, pp. 603-604).

239

Shafeek, M.R., Helmy, Y.I., Nadia, M.O. and Rizk, F.A., 2013. Effect of foliar fertilizer with

nutritional compound and humic acid on growth and yield of broad bean plants under

sandy soil conditions. Journal of Applied and Scientific Research, 9(6), pp. 3674-3680.

Shah, S.T.H., Zamir, M.S.I., Waseem, M., Ali, A., Tahir, M. and Khalid, W.B., 2009. Growth

and yield response of maize (Zea mays L.) to organic and inorganic sources of nitrogen.

Pakistan Journal of Life and Social Sciences, 7(2), pp. 108-111.

Shah, Z. and Khan, A.A., 2003. Evaluation of crop residues for mineralizable nitrogen in soils.

Sarhad Journal of Agriculture, 19(1), pp. 81-92.

Shah, Z., Shah, S.H., Peoples, M.B., Schwenke, G.D. and Herridge, D.F., 2003. Crop residue and

fertilizer N effects on nitrogen fixation and yields of legume-cereal rotations and soil

organic fertility. Field Crops Research, 83(1), pp. 1-11.

Shaheb, M.R., Islam, M.N., Nessa, A., Hossain, M.A. and Sarker, A., 2016. Impact of harvest

stage on seed yield quality and storability of french bean. Bangladesh Journal of


Shahryari, R., Khayatnezhad, M., Moghanlou, B.S., Khaneghah, A.M.P. and Gholamin, R.,

2011. Response of maize genotypes to changes in chlorophyll content at presence of

two types humic substances. Advances in Environmental Biology, 5(1), pp. 154-156.

Shanti, K., Rao, V.P., Reddy, M.R., Reddy, M.S. and Sarma, P.S., 1997. Response of maize (Zea

mays L.) hybrid and composite to different levels of nitrogen. Indian Journal of


Sharar, M.S., Ayub, M., Nadeem, M.A. and Ahmad, N., 2003. Effect of different rates of nitrogen

and phosphorus on growth and grain yield of maize (Zea mays L.). Asian Journal of Plant

Sciences, 2(3), pp. 347-349.

Sharif, M., 2002. Effect Of Lignitic Coal Derived Humic Acid On Growth And Yield Of Wheat

And Maize In Alkaline Soil (Doctoral dissertation, University Of Agri., Peshawar).

Sharif, M. and Sarir, M.S., 2002. Utilization of humic acid as a manure for increased crop

production. Scientific Khyber, 51(1), pp. 113-125.

Sharif, M., Khattak, R.A. and Sarrir, M.S., 2002. Effect of different levels of lignitic coal derived

humic acid on growth of maize plants. Communications in Soil Science and Plant

Analysis, 33(19-20), pp. 3567-3580.

240

Sharif, M., Khattak, R.A. and Sarir, M.S., 2002. Effect of different levels of lignitic coal

derived humic acid on growth of surface-irrigated wheat. Agricultural Science, 52, pp.

207-210.

Sharif, M., Ahmad, M., Sarir, M.S. and Khattak, R.A., 2004. Effect of organic and inorganic

fertilizers on the yield and yield components of maize. Pakistan Journal of Agriculture,

Agricultural Engineering and Veterinary Sciences, 20(1), pp. 11-16.

Sharif, M., Khattak, R.A. and Sarir, M.S., 2003. Residual effect of humic acid and chemical

fertilizers on maize yield and nutrient accumulation. Sarhad Journal of Agriculture, 19(4),

pp. 543-550.

Sharifai, A.I., Mahmud, M., Tanimu, B. and Abubakar, I.U., 2012. Yield and yield components

of extra early maize (Zea mays L.) as influenced by intra-row spacing, nitrogen and

poultry manure rates. Bayero Journal of Pure and Applied Sciences, 5(1), pp. 113-122.

Sharifai, A.I., Mahmud, M., Mahadi, M.A., Kura, H.N. and Namakka, A., 2008. Effect of

different levels of NPK compound fertilizer on growth parameters of extra-early maize

(Zea mays L.) varieties. Journal of Agricultural Research and Policies, 3(2), pp. 65-69.

Sharifi, P., 2017. Studying maize growth indices in different water stress conditions and the

use of humic acid. Biomedical and Pharmacology Journal, 10(1): 303-310

Sharifi, R.S. and Taghizadeh, R., 2009. Response of maize (Zea mays L.) cultivars to different

levels of nitrogen fertilizer. Journal of Food, Agriculture and Environment, 7(3-4), pp.

518-521.

Shazma, A., Iqbal, F., Khattak, W.A., Islam, M., Iqbal, B. and Khan, S., 2016. Response of wheat

crop to humic acid and nitrogen levels. Ec Agriculture, 3.1(2016), pp. 558-565.

Shivamurthy, D., 2005. Effect Of Method Of Planting And Seed Treatments On The Performance

Of Wheat Genotypes Under Rainfed Condition (Doctoral dissertation, UAS, Dharwad).

Shivay, Y.S. and Singh, R.P., 2000. Growth, yield attributes, yields and nitrogen uptake of maize

(Zea mays L.) as influenced by cropping systems and nitrogen levels. Annals of


Shrestha, J., 2013. Effect of nitrogen and plant population on flowering and grain yield of winter

maize. Sky Journal of Agricultural Research, 2(5), pp. 64-68.

241

Shuixiu, H. and Ruizhen, W., 2001. A study on the effect of komix, humic acid containing organic

fertilizer on spring soybean. Jiangxi Nongye Daxue Xuebao, 23(4), pp. 463-466.

Sibanda, H.M. and Young, S.D., 1986. Competitive adsorption of humus acids and phosphate on

goethite, gibbsite and two tropical soils. European Journal of Soil Science, 37(2), pp. 197-

204.

Sibanda, H.M. and Young, S.D., 1989. Effect of HA and soil heating on availability of P in oxide-

rich tropical soils, Publ. No. 9. British Ecological Society, Oxford, UK.

Sinclair, T.R. and Muchow, R.C., 1995. Effect of nitrogen supply on maize yield: I. Modeling

physiological responses. Agronomy Journal, 87(4), pp. 632-641.

Sinclair, T.R. and Vadez, V., 2002. Physiological traits for crop yield improvement in low N

and P environments. Plant and Soil, 245(1), pp. 1-15.

Singaravel, R.., Balasubramanian, T.N. and Govindasamy, R., 1993. Effect of humic acids on

sesame (Sesamum indicum L.) growth and yield under two nitrogen levels. Indian Journal

of Agronomy, 38(1), pp. 147-149.

Singh, K.B. and Saxena, M.C., 1990. Studies on drought tolerance: Annual report.

Accomplishments and Future Challenges in Dry Land Soil Fertility Research in The

Mediterranean Area, ICARDA, Aleppo, Syria.

Sivasankar, S., Collinson, S., Gupta, R. and Dhugga, K.S., 2012. 16 Maize. Handbook of

Bioenergy Crop Plants, p. 405.

Smith, M.E., Miles, C.A. and Van Beem, J., 1995. Genetic improvement of maize for nitrogen

use efficiency. Maize Research for Stress Environment, pp. 39-43.

Sola, M.G.P., Lales, J.S., Villegas, G.M. and Tagle, A.L., 2004. Response of recycled hybrid

maize (Zea mays L.) to different levels of nitrogen application. Philippine Journal of

Science, 133(1), pp. 23-31.

Soltanpour, P.A. and Schwab, A.P., 1977. A new soil test for simultaneous extraction of macro

and micro nutrients in alkaline soils. Communications in Soil Science and Plant

Analysis, 8(3), pp.195-207.

Sorkhi, F. and Fateh, M., 2014. Effect of nitrogen fertilizer on yield component of maize.

International Journal of Biosciences, 5(6), pp.16-20.

242

Spaccini, R., Piccolo, A., Conte, P., Haberhauer, G. and Gerzabek, M.H., 2002. Increased soil

organic carbon sequestration through hydrophobic protection by humic substances. Soil

Biology and Biochemistry, 34(12), pp. 1839-1851.

Squires, E., 2013. The impact of different nitrogen fertilizer rates on soil characteristics, plant

properties, and economic returns in a Southeastern Minnesota cornfield.

Sreewarome, A., Saensupo, S., Prammanne, P. and Weerathworn, P., 2007. Effect of rate and split

application of nitrogen on agronomic characteristics, cane yield and juice quality.

Proceedings International Society of Sugar Cane Technologists, 26, pp. 465-490.

Stewart, W.M., Dibb, D.W., Johnston, A.E. and Smyth, T.J., 2005. The contribution of

commercial fertilizer nutrients to food production. Agronomy Journal, 97(1), pp. 1-6.

Stone, P.J., Sorensen, I.B. and Reid, J.B., 1998. Effect of plant population and nitrogen fertiliser

on yield and quality of super sweet corn. In Proceedings of Annual Conference of

Agronomy Society of New Zealand (Vol. 28, pp. 1-5).

Subedi, K.D. and Ma, B.L., 2005. Nitrogen uptake and partitioning in stay-green and leafy maize

hybrids. Crop Science, 45(2), pp. 740-747.

Suganya, S. and Sivasamy, R., 2006. Moisture retention and cation exchange capacity of sandy

soil as influenced by soil additives. Journal of Applied Sciences Resrach, 2(11), pp. 949-

951.

Susilawati, K., Osumanu, H.A., Nik, M., Mohd, K.Y. and Mohamadu, B.J., 2009. Effect of

organic based N fertilizer on dry matter (Zea mays L.), ammonium and nitrate recovery in

an acid soil of Sarawak, Malaysia. American Journal of Applied Sciences, 6(7), pp. 1289-

1294.

Swanston, C., Homann, P.S., Caldwell, B.A., Myrold, D.D., Ganio, L. and Sollins, P., 2004.

Long-term effects of elevated nitrogen on forest soil organic matter

stability. Biogeochemistry, 70(2), pp. 229-252.

Swift, R.S. and Spark, K.M., 2001, January. Understanding and managing organic matter in

soils, sediments, and waters: Proceedings of the 9th International Conference of the

International Humic Substances Society. In 9th International Meeting of the

Inrernational Humic Substances Society.

243

Sylvester-Bradley, R. and Kindred, D.R., 2009. Analysing nitrogen responses of cereals to

prioritize routes to the improvement of nitrogen use efficiency. Journal of Experimental

Botany, 60(7), pp. 1939-1951.

Sylvia, D.M., Fuhrmann, J.J., Hartel, P.G. and Zuberer, D.A. eds., 2005. Principles and

Applications of Soil Microbiology (No. QR111 S674 2005). Upper Saddle River, NJ:

Pearson Prentice Hall.

Tadesse, D., 2012. Evaluation of improved maize genotypes for grain yield and yield components

in Chilga District, North Western Ethiopi. International Journal of Science and Research,

3(10), pp. 1362-1364.

Taghizadeh, R. and Sharifi, R.S., 2011. Effect of nitrogen fertilizer on yield attributes and nitrogen

use efficiency in corn cultivars. JWSS-Isfahan University of Technology, 15(57), pp. 209-

217.

Tagne, A., Feujio, T.P. and Sonna, C., 2008, October. Essential oil and plant extracts as potential

substitutes to synthetic fungicides in the control of fungi. In International Conference

Diversifying Crop Protection (pp. 12-15).

Tahir, M., Tanveer, A., Ali, A., Abbas, M. and Wasaya, A., 2008. Comparative yield performance

of different maize (Zea mays L.) hybrids under local conditions of Faisalabad, Pakistan.

Pakistan Journal of Life and Social Sciences, 6(2), pp. 118-120.

Tahir, M.M., Khurshid, M., Khan, M.Z., Abbasi, M.K. and Kazmi, M.H., 2011. Lignite-derived

humic acid effect on growth of wheat plants in different soils. Pedosphere, 21(1), pp. 124-

131.

Tan, K.H. and Tantiwiramanond, D., 1983. Effect of humic acids on nodulation and dry matter

production of soybean, peanut, and clover. Soil Science Society of America Journal, 47(6),

pp. 1121-1124.

Tan, K.H., 2003. Humic Matter in Soil and Environment, Principles and Controversies. CRC

Press.

Tesar, M.B., 1984. Physiological Basis of Crop Growth and Development (No. 581.31 P578).

American Society of Agronomy, Madison, Wis.(EUA) Crop Science Society of America,

Madison, Wis.(EUA).

Tian, Q., Chen, F., Zhang, F. and Mi, G., 2005. Possible involvement of cytokinin in nitrate-

mediated root growth in maize. Plant and Soil, 277(1-2), pp. 185-196.

244

Tolessa, D., Du Preez, C.C. and Ceronio, G.M., 2007. Comparison of maize genotypes for grain

yield, nitrogen uptake and use efficiency in western Ethiopia. South African Journal of

Plant and Soil, 24(2), pp. 70-76.

Tollenaar, M., McCullough, D.E. and Dwyer, L.M., 1994. Physiological basis of the genetic

improvement of corn. In: Slafer, G.A. (Ed.). Genetic Improvement of Field Crops. New

York. Pp. 183-236.

Tollenaar, M. and Lee, E.A., 2002. Yield potential, yield stability and stress tolerance in maize.

Field Crop Research, 75(2-3), pp. 161-169.

Tollenaar, M. and Wu. J., 1999. Yield improvement in temperate maize is attributable to greater

stress tolerance. Crop Science, 39(6), pp. 1597-1604.

Trapani, N., Hall, A.J. and Weber, M., 1999. Effects of constant and variable nitrogen supply on

sunflower (Helianthus annuus L.) leaf cell number and size. Annals of Botany, 84(5), pp.

599-606.

Tsai, C.Y., Dweikat, I., Huber, D.M. and Warren, H.L., 1992. Interrelationship of nitrogen

nutrition with maize (Zea mays L.) grain yield, nitrogen use efficiency and grain quality.

Journal of the Science of Food and Agriculture, 58(1), pp. 1-8.

Turgut, I., 2004. Effects of plant populations and nitrogen doses on fresh ear yield and yield

components of sweet corn (Zea mays saccharata Sturt.) grown under Bursa conditions.

Turkish Journal of Agriculture and Forestry, 24(3), pp. 341-348.

Turkmen, Ö., Dursun, A., Turan, M. and Erdinc, C., 2004. Calcium and humic acid affect seed

germination, growth, and nutrient content of tomato (Lycopersicon esculentum L.)

seedlings under saline soil conditions. Acta Agriculturae Scandinavica, 54(3), pp. 168-

174.

Uhart, S.A. and Andrade, F.H., 1995. Nitrogen deficiency in maize. 1. Effect on crop growth,

development, dry matter partitioning and kernel set. Crop Science, 35(5), pp. 1376-1383.

Ulger, A.C., Ibrikci, H., Cakir, B. and Guzel, N., 1997. Influence of nitrogen rates and row spacing

on corn yield, protein content, and other plant parameters. Journal of Plant Nutrition,

20(12), pp. 1697-1709.

Ullah, M.I., Khakwani, A.A., Sadiq, M., Awan, I., Munir, M. and Ghazanfarullah., 2015. Effects

of nitrogen fertilization rates on growth, quality and economic return of fodder maize (Zea

mays L.). Sarhad Journal of Agriculture, 31(1), pp. 45-52.

245

Unlu, H.O., Husnu, U.N.L.U. and Karakurt, Y., 2011. Changes in fruit yield and quality in

response to foliar and soil humic acid application in cucumber. Scientific Research and

Essays, 6(13), pp. 2800-2803.

Uribelarrea, M., Crafts-Brandner, S.J. and Below, F.E., 2009. Physiological N response of field-

grown maize hybrids (Zea mays L.) with divergent yield potential and grain protein

concentration. Plant and Soil, 316(1-2), pp. 151-160.

Utobo, E.B., Okporie, E.O., Oselebe, H.O., Ekwu, L.G., Ogah E.O. and Nwokwu, G.N., 2010.

Evaluation of eleven varieties of maize (Zea mays L.) in Abakaliki Agricultural area,

Southern Eastern Nigeria. Continental Journal of Agricultural Science, 4, pp. 42-47.

Vaccaro, S., Ertani, A., Nebbioso, A., Muscolo, A., Quaggiotti, S., Piccolo, A. and Nardi, S., 2015.

Humic substances stimulate maize nitrogen assimilation and amino acid metabolism at

physiological and molecular level. Chemical and Biological Technologies in Agriculture,

2(1), p. 5.

Valadabadi, S.A. and Farahani, H.A., 2010. Effects of planting density and pattern on

physiological growth indices in maize (Zea mays L.) under nitrogenous fertilizer

application. Journal of Agricultural Extension and Rural Development, 2(3), pp. 40-47.

Valentinuz, O.R. and Tollenaar, M., 2006. Effect of genotype, nitrogen, plant density, and row

spacing on the area per leaf profile in maize. Agronomy Journal, 98(1), pp. 94-99.

Vallini, G., Pera, A., Agnolucci, M. and Valdrighi, M.M., 1997. Humic acids stimulate growth

and activity of invitro tested axenic cultures of soil autotrophic nitrifying bacteria. Biology

and Fertility of Soils, 24(3), pp. 243-248.

Varanini, Z., Pinton, R., Behnke, H.D., Luttge, U., Esser, K., Kadereit, J.W. and Runge, M., 1995.

Humic substances and plant nutrition. Progress in Botany: Structural botany, physiology,

genetics and taxonomy. Geobotany, 56, pp. 97-117.

Varanini, Z. and Pinton, R., 2000. Direct versus indirect effects of soil humic substances on plant

growth and nutrition. The Rhizosphere. Marcel Dekker, New York, pp. 141-157.

Vaughan, D. and Malcolm, R.E., 1985. Influence of humic substances on growth and

physiological processes. In Soil Organic Matter and Biological Activity (pp. 37-75).

Springer, Dordrecht.

Vaughan, D. and Ord, B.G., 1991. Influence of natural and synthetic humic substances on the

activity of urease. European Journal of Soil Science, 42(1), pp. 17-23.

246

Wagner, G.H. and Wolf, D.C., 1999. Carbon Transformations and Soil Organic Matter Formation.

In: Sylvia, D.M., Fuhrmann, J.J. et al. (eds.). Principles and Applications of Soil

Microbiology. Prentice-Hall, Upper Saddle River, NJ. Pp. 285-331.

Wang, X.J., Wang, Z.Q. and Li, S.G., 1995. The effect of humic acids on the availability of

phosphorus fertilizers in alkaline soils. Soil Use and Management, 11(2), pp. 99-102.

Wang, Y., Mi, G., Chen, F. and Zhang, F., 2003. Genotypic differences in nitrogen uptake by

maize inbred lines its relation to root morphology. Acta Ecologica Sinica, 23(2), pp. 297-

302.

Wang, Y.P., Houlton, B.Z. and Field, C.B., 2007. A model of biogeochemical cycles of carbon,

nitrogen, and phosphorus including symbiotic nitrogen fixation and phosphatase

production. Global Biogeochemical Cycles, 21(1), pp. 1018-1029.

Waqas, M.A., 2002. The Growth and Yield Response of Two Maize Hybrids to Different Levels

of Nitrogen. (Doctoral dissertation, Thesis Uni. Agri. Faisalabad).

Wardle, D.A., 2005. How plant communities influence decomposer communities. In: Bardgett

R.D., Usher, M.B. and Hopkins, D.W. (Eds.). Biological Diversity and Function in Soils,

pp. 119-138.

Watson, D.J., 1947. Comparative physiological studies on the growth of field crops II. The effect

of varying nutrient supply on net assimilation rate and leaf area. Annals of Botany, 11(4),

pp. 375-407.

Widdicombe, W.D. and Thelen, K.D., 2002. Row width and plant density effects on corn grain

production in the Northern Corn belt. Agronomy Journal, 94(5), pp. 1020-1023.

Wiesler, F., Behrens, T. and Horst, W.J., 2001. The role of N efficient cultivars in sustainable

agriculture. The Scientific World Journal, 1, pp. 61-69.

Xavier, D.M., Silva, A.S., Santos, R.P., Mesko, M.F., Costa, S.N., Freire, V.N., Cavada, B.S. and

Martins, J.L., 2012. Characterization of the coal humic acids from the Candiota coal field,

Brazil. International Journal of Agriculture Sciences, 4(5), pp. 238-242.

Yadav, J.U.H.I., Yadav, S.W.A.T.I. and Singh, S.G., 2011. Plant growth promotion in wheat crop

under environmental condition by PSB as bio-fertilizer. Research Journal of Agricultural

Sciences, 2(1), pp. 76-78.

247

Yadav, R.L., Kumar, R. and Verma, R.S., 1990. Effects of nitrogen applied through new carriers

on yield and quality of sugarcane. The Journal of Agricultural Science, 114(2), pp. 225-

230.

Yang, C.M., Wang, M.C., Lu, Y.F., Chang, F. and Chou, C.H., 2004. Humic substances affect the

activity of chlorophyllase. Journal of Chemical Ecology, 30(5), pp. 1057-1065.

Yang, J.Y., Huffman, E.C., De Jong, R., Kirkwood, V., MacDonald, K.B. and Drury, C.F., 2007.

Residual soil nitrogen in soil landscapes of Canada as affected by land use practices and

agricultural policy scenarios. Land Use Policy, 24(1), pp. 89-99.

Yildirim, E., 2007. Foliar and soil fertilization of humic acid affect productivity and quality of

tomato. Acta Agriculturae Scandinavica, 57(2), pp. 182-186.

Ying, J., Lee, E.A. and Tollenaar, M., 2000. Response of maize leaf photosynthesis to low

temperature during grain filling period. Field Crops Research, 68(2), pp. 87-96.

Yingei, W., 1988. Humic acid resin treatment of copper and nickle. Haunjing Bashu, 7, pp. 21-

22.

Younas, M., Rehman, H. and Hayder, G., 2002. Magnitude of variability for yield and yield

associated traits in maize hybrids. Asian Journal of Plant Science, 1(6), pp. 694-696.

Zancani, M., Petrussa, E., Krajňáková, J., Casolo, V., Spaccini, R., Piccolo, A., Macrì, F. and

Vianello, A., 2009. Effect of humic aids on phosphate level and energetic metabolism of

tobacco BY-2 suspension cell cultures. Environmental and Experimental Botany, 65(2-3),

pp. 287-295.

Zandonadi, D.B., Canellas, L.P. and Facanha, A.R., 2007. Indolacetic and humic acids induce

lateral root development through a concerted plasmalemma and tonoplast H+ pumps

activation. Planta, 225(6), pp. 1583-1595.

Zdunic, Z., Mijic, A., Dugalic, K., Simic, D., Brkic, J. and Jeromela, A.M., 2008. Genetic analysis

of grain yield and starch content in nine maize populations. Turkish Journal of Agriculture

and Forestry, 32(6), pp. 495-500.

Zech, W., Senesi, N., Guggenberger, G., Kaiser, K., Lehmann, J., Miano, T.M., Miltner, A. and

Schroth, G., 1997. Factors controlling humification and mineralization of soil organic

matter in the tropics. Geoderma, 79(1-4), pp. 117-161.

248

Zeidan, M.S., Amany, A., Bahr, M. and El-Kramany, M.F., 2006. Effect of N-fertilizer and plant

density on yield and quality of maize in sandy soil. Research Journal of Agriculture and


Zhang, X.L., Wang, Q., Zhao, Y.L., Yang, Q.H. and Li, C.H., 2010. Effects of nitrogen

fertilization rate and harvest time on summer maize grain yield and its quality. Journal of

Applied Ecology, 21(10), pp. 2565-2572.

Zhang, Y.J., Yu-Ran, Z.H.O.U., Bin, D.U. and Jian-Chang, Y.A.N.G., 2008. Effects of nitrogen

nutrition on grain yield of upland and paddy rice under different cultivation methods. Acta

Agronomica, 34(6), pp. 1005-1013.

Zhao, R.F., Chen, X.P., Zhang, F.S., Zhang, H., Schroder, J. and Römheld, V., 2006. Fertilization

and nitrogen balance in a wheat-maize rotation system in North China. Agronomy

Journal, 98(4), pp. 938-945.

Zhong, H., Wang, Q., Zhao, X., Du, Q., Zhao, Y., Wang, X., Jiang, C., Zhao, S., Cao, M., Yu, H.

and Wang, D., 2014. Effects of different nitrogen applications on soil physical, chemical

properties and yield in maize (Zea mays L.). Agricultural Sciences, 5(14), pp. 1440-1447.

Zhong, Y., Yan, W., Chen, J. and Shangguan, Z., 2014. Net ammonium and nitrate fluxes in wheat

roots under different environmental conditions as assessed by scanning ion-selective

electrode technique. Scientific Reports, 4, p. 7223.

Zribi, W., Faci, J.M. and Aragues, R., 2011. Mulching effects on moisture, temperature, structure

and salinity of agricultural soils. ITEA-Informacion Tecnica Economica Agraria, 107(2),

pp. 148-162.

249

8. APPENDICES

Table 45. Combined statistical analysis of variance for days to emergence of

maize genotypes as affected by humic acid and nitrogen

SOV DF SS MS F value P value

Year 1 0.07 0.07 1.09 0.37

Reps within Y 4 0.24 0.06 1.30 0.43

Genotypes 3 6.20 2.07 44.89 0.01

G×Y 3 1.17 0.39 8.51 0.06

Error I 12 0.55 0.05

H 3 1.76 0.59 3.02 0.03

H×Y 3 2.24 0.75 3.85 0.01

H×G 9 0.45 0.15 0.77 0.51

H×G×Y 9 0.13 0.04 0.23 0.88

Error II 48 1.29 0.14 0.74 0.67

N 3 1.94 0.22 1.11 0.36

N×Y 3 0.88 0.10 0.50 0.87

N×H 9 1.73 0.19 0.99 0.45

N×H×Y 9 0.52 0.06 0.30 0.97

N×G 9 0.50 0.06 0.29 0.98

N×G×Y 9 4.70 0.17 0.90 0.62

N×H×G 27 5.38 0.20 1.03 0.43

N×H×G×Y 27 46.54 0.19

Error III 192 76.29

Total 383 0.07 0.07 1.09 0.37

DF = Degrees of freedom, SS = Sum of squares, MS = Mean square, F value = Fisher

value, P value = Probability value

250

Table 46. Combined statistical analysis of variance for days to 50% tasseling of



Year 1 444.19 444.19 23.23 0.02

Reps within Y 4 76.49 19.12

Genotypes 3 6369.97 2123.32 228.50 0.00

G×Y 3 51.82 17.27 1.86 0.19

Error I 12 111.51 9.29

H 3 726.82 242.27 965.74 0.00

H×Y 3 0.34 0.11 0.45 0.72

H×G 9 3.96 0.44 1.75 0.08

H×G×Y 9 1.36 0.15 0.60 0.80

Error II 48 16.50 0.34

N 3 1222.61 407.54 1185.56 0.00

N×Y 3 3.59 1.20 3.48 0.02

N×H 9 23.23 2.58 10.29 0.00

N×H×Y 9 1.67 0.19 0.74 0.67

N×G 9 13.09 1.45 4.23 0.00

N×G×Y 9 3.02 0.34 0.98 0.47

N×H×G 27 5.86 0.22 0.87 0.66

N×H×G×Y 27 4.84 0.18 0.71 0.85

Error III 192 48.17 0.25

Total 383 9129.04



251

Table 47. Combined statistical analysis of variance for days to 50% silking of



Year 1 551.04 551.04 13.34 0.04

Reps within Y 4 165.20 41.30

Genotypes 3 7082.34 2360.78 225.26 0.00

G×Y 3 63.40 21.13 2.02 0.17

Error I 12 125.76 10.48

H 3 1342.30 447.43 1174.13 0.00

H×Y 3 3.69 1.23 3.23 0.02

H×G 9 3.51 0.39 1.02 0.42

H×G×Y 9 0.96 0.11 0.28 0.98

Error II 48 27.88 0.58

N 3 2175.09 725.03 1248.48 0.00

N×Y 3 1.85 0.62 1.06 0.37

N×H 9 14.51 1.61 4.23 0.00

N×H×Y 9 2.08 0.23 0.61 0.79

N×G 9 12.47 1.39 2.39 0.03

N×G×Y 9 3.71 0.41 0.71 0.70

N×H×G 27 10.84 0.40 1.05 0.40

N×H×G×Y 27 4.94 0.18 0.48 0.99

Error III 192 73.17 0.38

Total 383 11664.74



252

Table 48. Combined statistical analysis of variance for ASI (anthesis to silking

interval) of maize genotypes as affected by humic acid and nitrogen


Year 1 6.25 6.25 1.27 0.34


Genotypes 3 23.20 7.73 27.83 0.00

G×Y 3 0.24 0.08 0.28 0.84

Error I 12 3.33 0.28

H 3 87.88 29.29 228.02 0.00

H×Y 3 1.22 0.41 3.16 0.03

H×G 9 0.42 0.05 0.36 0.95

H×G×Y 9 0.25 0.03 0.22 0.99

Error II 48 7.00 0.15

N 3 135.13 45.04 308.88 0.00

N×Y 3 0.97 0.32 2.21 0.10

N×H 9 2.82 0.31 2.43 0.01

N×H×Y 9 0.19 0.02 0.16 1.00

N×G 9 1.75 0.19 1.34 0.24

N×G×Y 9 0.59 0.07 0.45 0.90

N×H×G 27 3.51 0.13 1.01 0.46

N×H×G×Y 27 1.80 0.07 0.52 0.98

Error III 192 24.67 0.13

Total 383 320.87



253

Table 49. Combined statistical analysis of variance for days to physiological

maturity of maize genotypes as affected by humic acid and nitrogen


Year 1 448.50 448.50 57.03 0.00


Genotypes 3 21669.42 7223.14 535.87 0.00

G×Y 3 295.22 98.41 7.30 0.00

Error I 12 161.75 13.48

H 3 602.65 200.88 570.00 0.00

H×Y 3 1.65 0.55 1.56 0.20

H×G 9 22.92 2.55 7.23 0.00

H×G×Y 9 4.25 0.47 1.34 0.22

Error II 48 47.79 1.00

N 3 1352.72 450.91 452.87 0.00

N×Y 3 16.30 5.43 5.46 0.00

N×H 9 15.04 1.67 4.74 0.00

N×H×Y 9 3.75 0.42 1.18 0.31

N×G 9 33.77 3.75 3.77 0.00

N×G×Y 9 2.36 0.26 0.26 0.98

N×H×G 27 7.84 0.29 0.82 0.72

N×H×G×Y 27 5.47 0.20 0.57 0.96

Error III 192 67.67 0.35

Total 383 24790.54



254

Table 50. Combined statistical analysis of variance for seed fill duration (SFD)

of maize genotypes as affected by humic acid and nitrogen


Year 1 1993.82 1993.82 69.57 0.00

Reps within Y 4 114.64 28.66

Genotypes 3 4278.11 1426.04 124.09 0.00

G×Y 3 450.72 150.24 13.07 0.00

Error I 12 137.91 11.49

H 3 3787.01 1262.34 2135.41 0.00

H×Y 3 8.40 2.80 4.74 0.00

H×G 9 22.38 2.49 4.21 0.00

H×G×Y 9 4.52 0.50 0.85 0.57

Error II 48 81.96 1.71

N 3 6940.90 2313.63 1355.01 0.00

N×Y 3 26.72 8.91 5.22 0.00

N×H 9 55.17 6.13 10.37 0.00

N×H×Y 9 3.77 0.42 0.71 0.70

N×G 9 44.32 4.92 2.88 0.01

N×G×Y 9 6.54 0.73 0.43 0.91

N×H×G 27 12.99 0.48 0.81 0.73

N×H×G×Y 27 12.01 0.44 0.75 0.81

Error III 192 113.50 0.59

Total 383 18095.37



255

Table 51. Combined statistical analysis of variance for total weight (g) plant-1 of

maize genotypes at silking as affected by humic acid and nitrogen


Year 1 1824.57 1824.57 20.52 0.02

Reps within Y 4 355.62 88.90

Genotypes 3 99665.77 33221.92 486.20 0.00

G×Y 3 376.73 125.58 1.84 0.19

Error I 12 819.96 68.33

H 3 5886.74 1962.25 1551.78 0.00

H×Y 3 18.18 6.06 4.79 0.00

H×G 9 130.29 14.48 11.45 0.00

H×G×Y 9 45.18 5.02 3.97 0.00

Error II 48 528.16 11.00

N 3 109873.54 36624.51 3328.47 0.00

N×Y 3 76.48 25.49 2.32 0.09

N×H 9 84.96 9.44 7.47 0.00

N×H×Y 9 16.79 1.87 1.48 0.16

N×G 9 3354.19 372.69 33.87 0.00

N×G×Y 9 358.65 39.85 3.62 0.00

N×H×G 27 100.35 3.72 2.94 0.07

N×H×G×Y 27 99.15 3.67 2.90 0.00

Error III 192 242.79 1.26

Total 383 223858.10



256

Table 52. Combined statistical analysis of variance for ear weight (g) plant-1 of



Year 1 450.69 450.69 15.45 0.03

Reps within Y 4 116.71 29.18

Genotypes 3 5155.54 1718.51 464.36 0.00

G×Y 3 10.08 3.36 0.91 0.47

Error I 12 44.41 3.70

H 3 547.83 182.61 1428.06 0.00

H×Y 3 0.59 0.20 1.54 0.21

H×G 9 1.83 0.20 1.59 0.12

H×G×Y 9 1.36 0.15 1.18 0.31

Error II 48 81.28 1.69

N 3 10203.40 3401.13 2008.47 0.00

N×Y 3 0.30 0.10 0.06 0.98

N×H 9 0.81 0.09 0.71 0.70

N×H×Y 9 2.86 0.32 2.48 0.01

N×G 9 65.77 7.31 4.32 0.00

N×G×Y 9 5.99 0.67 0.39 0.93

N×H×G 27 4.43 0.16 1.28 0.17

N×H×G×Y 27 1.84 0.07 0.53 0.97

Error III 192 24.55 0.13

Total 383 16720.27



257

Table 53. Combined statistical analysis of variance for plant height (cm) of



Year 1 3243.37 3243.37 222.35 0.00


Genotypes 3 73524.36 24508.12 1910.52 0.00

G×Y 3 310.82 103.61 8.08 0.00

Error I 12 153.94 12.83

H 3 1368.07 456.02 528.64 0.00

H×Y 3 3.11 1.04 1.20 0.31

H×G 9 20.24 2.25 2.61 0.01

H×G×Y 9 16.76 1.86 2.16 0.03

Error II 48 277.10 5.77

N 3 33944.36 11314.79 1959.96 0.00

N×Y 3 130.10 43.37 7.51 0.00

N×H 9 8.15 0.91 1.05 0.40

N×H×Y 9 6.37 0.71 0.82 0.60

N×G 9 373.33 41.48 7.19 0.00

N×G×Y 9 30.09 3.34 0.58 0.81

N×H×G 27 34.21 1.27 1.47 0.07

N×H×G×Y 27 17.02 0.63 0.73 0.83

Error III 192 165.63 0.86

Total 383 113685.39



258

Table 54. Combined statistical analysis of variance for AGR (g plant-1 day-1) of



Year 1 1.77 1.77 36.03 0.01


Genotypes 3 8.47 2.82 97.62 0.00

G×Y 3 0.30 0.10 3.52 0.05

Error I 12 0.35 0.03

H 3 5.35 1.78 2045.26 0.00

H×Y 3 0.01 0.00 2.96 0.03

H×G 9 0.04 0.00 4.57 0.00

H×G×Y 9 0.02 0.00 2.57 0.01

Error II 48 0.20 0.00

N 3 44.56 14.85 3644.62 0.00

N×Y 3 0.02 0.01 1.94 0.14

N×H 9 0.25 0.03 31.70 0.00

N×H×Y 9 0.01 0.00 1.72 0.09

N×G 9 0.41 0.05 11.29 0.00

N×G×Y 9 0.15 0.02 3.97 0.00

N×H×G 27 0.05 0.00 2.14 0.00

N×H×G×Y 27 0.04 0.00 1.72 0.02

Error III 192 0.17 0.00

Total 383 62.36



259

Table 55. Combined statistical analysis of variance for CGR (g m-2 day-1) of



Year 1 109.47 109.47 47.89 0.01


Genotypes 3 325.79 108.60 96.76 0.00

G×Y 3 13.84 4.61 4.11 0.03

Error I 12 13.47 1.12

H 3 248.26 82.75 1508.11 0.00

H×Y 3 0.27 0.09 1.64 0.18

H×G 9 1.83 0.20 3.70 0.00

H×G×Y 9 1.65 0.18 3.35 0.00

Error II 48 7.20 0.15

N 3 2144.57 714.86 4767.04 0.00

N×Y 3 0.78 0.26 1.74 0.17

N×H 9 12.96 1.44 26.24 0.00

N×H×Y 9 1.32 0.15 2.68 0.01

N×G 9 16.70 1.86 12.37 0.00

N×G×Y 9 6.63 0.74 4.91 0.00

N×H×G 27 2.89 0.11 1.95 0.07

N×H×G×Y 27 2.63 0.10 1.78 0.01

Error III 192 10.54 0.05

Total 383 2929.92



260

Table 56. Combined statistical analysis of variance for total weight (g) plant-1 of

maize genotypes at maturity as affected by humic acid and nitrogen


Year 1 1092.83 1092.83 15.47 0.03

Reps within Y 4 282.56 70.64

Genotypes 3 462361.85 154120.62 4795.24 0.00

G×Y 3 24.36 8.12 0.25 0.86

Error I 12 385.68 32.14

H 3 25707.76 8569.25 84.41 0.00

H×Y 3 197.79 65.93 0.65 0.58

H×G 9 2386.97 265.22 2.61 0.01

H×G×Y 9 1426.96 158.55 1.56 0.13

Error II 48 5587.39 116.40

N 3 515463.23 171821.08 1476.07 0.00

N×Y 3 765.89 255.30 2.19 0.10

N×H 9 1848.60 205.40 2.02 0.04

N×H×Y 9 716.39 79.60 0.78 0.63

N×G 9 17529.89 1947.77 16.73 0.00

N×G×Y 9 1246.87 138.54 1.19 0.32

N×H×G 27 3351.18 124.12 1.22 0.22

N×H×G×Y 27 2817.75 104.36 1.03 0.43

Error III 192 19490.89 101.52

Total 383 1062684.83



261

Table 57. Combined statistical analysis of variance for AGR (g plant-1 day-1) of



Year 1 0.04 0.04 3.89 0.14


Genotypes 3 14.15 4.72 312.00 0.00

G×Y 3 0.24 0.08 5.33 0.01

Error I 12 0.18 0.02

H 3 1.13 0.38 37.74 0.00

H×Y 3 0.02 0.01 0.73 0.54

H×G 9 0.11 0.01 1.26 0.26

H×G×Y 9 0.16 0.02 1.75 0.08

Error II 48 0.57 0.01

N 3 45.91 15.30 1289.45 0.00

N×Y 3 0.11 0.04 3.04 0.04

N×H 9 0.28 0.03 3.15 0.00

N×H×Y 9 0.07 0.01 0.77 0.65

N×G 9 0.54 0.06 5.09 0.00

N×G×Y 9 0.13 0.01 1.20 0.32

N×H×G 27 0.37 0.01 1.38 0.11

N×H×G×Y 27 0.29 0.01 1.09 0.36

Error III 192 1.91 0.01

Total 383 66.26



262

Table 58. Combined statistical analysis of variance for CGR (g m-2 day-1) of


SOV DF SS MS F P

Year 1 56.91 56.91 33.44 0.01


Genotypes 3 998.88 332.96 443.64 0.00

G×Y 3 33.99 11.33 15.10 0.00

Error I 12 9.01 0.75

H 3 124.05 41.35 80.51 0.00

H×Y 3 1.24 0.41 0.80 0.49

H×G 9 2.41 0.27 0.52 0.86

H×G×Y 9 5.06 0.56 1.09 0.37

Error II 48 29.88 0.62

N 3 3890.76 1296.92 2083.32 0.00

N×Y 3 3.22 1.07 1.72 0.17

N×H 9 15.89 1.77 3.44 0.00

N×H×Y 9 5.88 0.65 1.27 0.25

N×G 9 15.87 1.76 2.83 0.01

N×G×Y 9 10.69 1.19 1.91 0.07

N×H×G 27 23.24 0.86 1.68 0.02

N×H×G×Y 27 16.84 0.62 1.21 0.22

Error III 192 98.62 0.51

Total 383 5349.24



263

Table 59. Combined statistical analysis of variance for leaves plant-1 of maize

genotypes as affected by humic acid and nitrogen


Year 1 85.79 85.79 109.62 0.00


Genotypes 3 121.86 40.62 390.68 0.00

G×Y 3 0.56 0.19 1.79 0.20

Error I 12 1.25 0.10

H 3 11.21 3.74 327.69 0.00

H×Y 3 0.04 0.01 1.04 0.38

H×G 9 0.29 0.03 2.84 0.00

H×G×Y 9 0.08 0.01 0.82 0.60

Error II 48 1.46 0.03

N 3 227.85 75.95 2499.17 0.00

N×Y 3 0.84 0.28 9.19 0.00

N×H 9 0.21 0.02 2.02 0.04

N×H×Y 9 0.16 0.02 1.52 0.14

N×G 9 2.70 0.30 9.85 0.00

N×G×Y 9 0.43 0.05 1.57 0.15

N×H×G 27 0.31 0.01 1.01 0.46

N×H×G×Y 27 0.19 0.01 0.62 0.93

Error III 192 2.19 0.01

Total 383 460.54



264

Table 60. Combined statistical analysis of variance for leaf dry weight (g) plant-

1 at silking stages of maize genotypes as affected by humic acid and

nitrogen


Year 1 810.33 810.33 17.10 0.03

Reps within Y 4 189.59 47.40

Genotypes 3 10335.67 3445.22 351.39 0.00

G×Y 3 18.82 6.27 0.64 0.60

Error I 12 117.65 9.80

H 3 646.56 215.52 69.43 0.00

H×Y 3 17.12 5.71 1.84 0.14

H×G 9 37.88 4.21 1.36 0.21

H×G×Y 9 24.15 2.68 0.86 0.56

Error II 48 166.82 3.48

N 3 9422.84 3140.95 903.77 0.00

N×Y 3 8.83 2.94 0.85 0.48

N×H 9 28.60 3.18 1.02 0.42

N×H×Y 9 26.78 2.98 0.96 0.48

N×G 9 195.07 21.67 6.24 0.00

N×G×Y 9 27.58 3.06 0.88 0.55

N×H×G 27 83.47 3.09 1.00 0.48

N×H×G×Y 27 85.21 3.16 1.02 0.45

Error III 192 595.98 3.10

Total 383 22838.96



265

Table 61. Combined statistical analysis of variance for leaf area (cm2) plant-1 at

silking stages of maize genotypes as affected by humic acid and

nitrogen


Year 1 2695763.94 2695763.94 16.09 0.03

Reps within Y 4 670286.22 167571.55

Genotypes 3 111136129.64 37045376.55 925.60 0.00

G×Y 3 157426.90 52475.63 1.31 0.32

Error I 12 480278.80 40023.23

H 3 6954162.69 2318054.23 417.46 0.00

H×Y 3 1528.99 509.66 0.09 0.96

H×G 9 82793.79 9199.31 1.66 0.10

H×G×Y 9 65322.29 7258.03 1.31 0.24

Error II 48 350709.81 7306.45

N 3 119418405.1 39806135.03 5448.08 0.00

N×Y 3 12095.28 4031.76 0.55 0.65

N×H 9 67606.44 7511.83 1.35 0.21

N×H×Y 9 48373.29 5374.81 0.97 0.47

N×G 9 2141711.11 237967.90 32.57 0.00

N×G×Y 9 122752.01 13639.11 1.87 0.08

N×H×G 27 166041.44 6149.68 1.11 0.33

N×H×G×Y 27 168409.60 6237.39 1.12 0.32

Error III 192 1066130.30 5552.76

Total 383 245805927.64



266

Table 62. Combined statistical analysis of variance for leaf area index (LAI) at

silking stages of maize genotypes as affected by humic acid and

nitrogen


Year 1 2.06 2.06 229.87 0.00


Genotypes 3 45.66 15.22 1204.69 0.00

G×Y 3 0.12 0.04 3.08 0.07

Error I 12 0.15 0.01

H 3 2.61 0.87 955.09 0.00

H×Y 3 0.01 0.00 5.23 0.00

H×G 9 0.08 0.01 9.53 0.00

H×G×Y 9 0.02 0.00 2.85 0.00

Error II 48 0.15 0.00

N 3 61.40 20.47 6491.01 0.00

N×Y 3 0.03 0.01 2.79 0.05

N×H 9 0.11 0.01 13.55 0.00

N×H×Y 9 0.01 0.00 1.49 0.15

N×G 9 0.91 0.10 32.11 0.00

N×G×Y 9 0.01 0.00 0.38 0.94

N×H×G 27 0.11 0.00 4.33 0.00

N×H×G×Y 27 0.04 0.00 1.70 0.02

Error III 192 0.17 0.00

Total 383 113.69



267

Table 63. Combined statistical analysis of variance for SLA (cm2 g-1) plant-1 of



Year 1 17891.60 17891.60 23.78 0.02

Reps within Y 4 3009.58 752.40

Genotypes 3 82789.42 27596.47 78.66 0.00

G×Y 3 783.90 261.30 0.74 0.55

Error I 12 4209.84 350.82

H 3 6014.90 2004.97 173.10 0.00

H×Y 3 51.27 17.09 1.48 0.22

H×G 9 412.13 45.79 3.95 0.00

H×G×Y 9 133.79 14.87 1.28 0.25

Error II 48 2785.18 58.02

N 3 85683.88 28561.29 492.23 0.00

N×Y 3 890.84 296.95 5.12 0.00

N×H 9 165.48 18.39 1.59 0.12

N×H×Y 9 308.39 34.27 2.96 0.00

N×G 9 2342.59 260.29 4.49 0.00

N×G×Y 9 447.97 49.77 0.86 0.57

N×H×G 27 437.71 16.21 1.40 0.10

N×H×G×Y 27 413.16 15.30 1.32 0.14

Error III 192 2223.83 11.58

Total 383 210995.45



268

Table 64. Combined statistical analysis of variance for LAR (cm2 g-1) plant-1 of



Year 1 29.41 29.41 1.23 0.35


Genotypes 3 3360.34 1120.11 44.95 0.00

G×Y 3 26.91 8.97 0.36 0.78

Error I 12 299.03 24.92

H 3 65.90 21.97 39.44 0.00

H×Y 3 2.49 0.83 1.49 0.22

H×G 9 3.94 0.44 0.79 0.63

H×G×Y 9 13.95 1.55 2.78 0.00

Error II 48 148.31 3.09

N 3 2643.16 881.05 285.15 0.00

N×Y 3 32.62 10.87 3.52 0.02

N×H 9 23.75 2.64 4.74 0.00

N×H×Y 9 6.91 0.77 1.38 0.20

N×G 9 173.50 19.28 6.24 0.00

N×G×Y 9 90.05 10.01 3.24 0.00

N×H×G 27 23.01 0.85 1.53 0.06

N×H×G×Y 27 15.21 0.56 1.01 0.46

Error III 192 106.94 0.56

Total 383 7160.92



269

Table 65. Combined statistical analysis of variance for productive plants m-2 of



Year 1 13.50 13.50 44.98 0.01


Genotypes 3 9.83 3.28 61.30 0.00

G×Y 3 2.41 0.80 15.00 0.00

Error I 12 0.64 0.05

H 3 2.59 0.86 538.52 0.00

H×Y 3 0.01 0.00 1.70 0.17

H×G 9 0.11 0.01 7.91 0.00

H×G×Y 9 0.02 0.00 1.16 0.32

Error II 48 0.61 0.01

N 3 71.27 23.76 1884.49 0.00

N×Y 3 0.78 0.26 20.64 0.00

N×H 9 0.22 0.02 15.50 0.00

N×H×Y 9 0.04 0.00 2.59 0.01

N×G 9 2.29 0.25 20.16 0.00

N×G×Y 9 0.16 0.02 1.41 0.21

N×H×G 27 0.08 0.00 1.80 0.01

N×H×G×Y 27 0.10 0.00 2.30 0.00

Error III 192 0.31 0.00

Total 383 106.16



270

Table 66. Combined statistical analysis of variance for ears plant-1 of maize



Year 1 0.20 0.20 73.78 0.00


Genotypes 3 0.35 0.12 75.05 0.00

G×Y 3 0.04 0.01 8.41 0.00

Error I 12 0.02 0.00

H 3 0.07 0.02 504.36 0.00

H×Y 3 0.00 0.00 0.84 0.47

H×G 9 0.00 0.00 2.92 0.00

H×G×Y 9 0.00 0.00 0.49 0.88

Error II 48 0.01 0.00

N 3 1.80 0.60 2580.67 0.00

N×Y 3 0.01 0.00 11.51 0.00

N×H 9 0.00 0.00 2.89 0.00

N×H×Y 9 0.00 0.00 0.65 0.75

N×G 9 0.03 0.00 16.35 0.00

N×G×Y 9 0.00 0.00 0.91 0.52

N×H×G 27 0.00 0.00 1.86 0.06

N×H×G×Y 27 0.00 0.00 1.46 0.08

Error III 192 0.01 0.00

Total 383 2.56



271

Table 67. Combined statistical analysis of variance for ears m-2 of maize



Year 1 14.36 14.36 50.49 0.01


Genotypes 3 13.09 4.36 55.52 0.00

G×Y 3 2.01 0.67 8.54 0.00

Error I 12 0.94 0.08

H 3 3.56 1.19 710.42 0.00

H×Y 3 0.01 0.00 2.94 0.03

H×G 9 0.05 0.01 3.16 0.00

H×G×Y 9 0.02 0.00 1.57 0.13

Error II 48 0.55 0.01

N 3 84.98 28.33 2491.82 0.00

N×Y 3 0.23 0.08 6.64 0.00

N×H 9 0.09 0.01 6.05 0.00

N×H×Y 9 0.05 0.01 3.46 0.00

N×G 9 1.53 0.17 14.99 0.00

N×G×Y 9 0.26 0.03 2.49 0.02

N×H×G 27 0.06 0.00 1.43 0.09

N×H×G×Y 27 0.09 0.00 1.96 0.00

Error III 192 0.32 0.00

Total 383 123.36



272

Table 68. Combined statistical analysis of variance for ear weight (g) plant-1 of



Year 1 1061.01 1061.01 31.35 0.01

Reps within Y 4 135.39 33.85

Genotypes 3 129670.30 43223.43 2128.52 0.00

G×Y 3 39.68 13.23 0.65 0.60

Error I 12 243.68 20.31

H 3 9492.81 3164.27 1285.30 0.00

H×Y 3 92.79 30.93 12.56 0.00

H×G 9 259.67 28.85 11.72 0.00

H×G×Y 9 52.01 5.78 2.35 0.02

Error II 48 270.16 5.63

N 3 201637.27 67212.42 11941.71 0.00

N×Y 3 205.94 68.65 12.20 0.00

N×H 9 214.82 23.87 9.70 0.00

N×H×Y 9 59.86 6.65 2.70 0.01

N×G 9 8074.70 897.19 159.40 0.00

N×G×Y 9 56.09 6.23 1.11 0.38

N×H×G 27 339.63 12.58 5.11 0.00

N×H×G×Y 27 154.68 5.73 2.33 0.00

Error III 192 472.68 2.46

Total 383 352533.18



273

Table 69. Combined statistical analysis of variance for ear length (cm) of maize



Year 1 0.73 0.73 9.68 0.05


Genotypes 3 585.09 195.03 1579.26 0.00

G×Y 3 0.23 0.08 0.61 0.62

Error I 12 1.48 0.12

H 3 27.68 9.23 810.42 0.00

H×Y 3 0.07 0.02 2.01 0.11

H×G 9 0.47 0.05 4.54 0.00

H×G×Y 9 0.63 0.07 6.14 0.00

Error II 48 1.65 0.03

N 3 1001.32 333.77 9729.27 0.00

N×Y 3 0.11 0.04 1.08 0.37

N×H 9 0.36 0.04 3.49 0.00

N×H×Y 9 0.39 0.04 3.80 0.00

N×G 9 12.98 1.44 42.04 0.00

N×G×Y 9 0.31 0.03 1.01 0.44

N×H×G 27 0.41 0.02 1.34 0.13

N×H×G×Y 27 0.25 0.01 0.82 0.72

Error III 192 2.19 0.01

Total 383 1636.65



274

Table 70. Combined statistical analysis of variance for ear girth (cm) of maize



Year 1 3.08 3.08 13.58 0.03


Genotypes 3 232.43 77.48 5036.14 0.00

G×Y 3 0.20 0.07 4.39 0.03

Error I 12 0.18 0.02

H 3 23.90 7.97 625.02 0.00

H×Y 3 0.53 0.18 13.81 0.00

H×G 9 0.40 0.04 3.49 0.00

H×G×Y 9 0.14 0.02 1.25 0.27

Error II 48 1.17 0.02

N 3 781.30 260.43 10668.66 0.00

N×Y 3 0.34 0.11 4.61 0.01

N×H 9 0.27 0.03 2.34 0.02

N×H×Y 9 0.09 0.01 0.82 0.60

N×G 9 6.82 0.76 31.03 0.00

N×G×Y 9 0.49 0.05 2.21 0.04

N×H×G 27 0.96 0.04 2.78 0.00

N×H×G×Y 27 0.42 0.02 1.23 0.21

Error III 192 2.45 0.01

Total 383 1056.08



275

Table 71. Combined statistical analysis of variance for rows ear-1 of maize



Year 1 8.93 8.93 233.92 0.00


Genotypes 3 63.43 21.14 84.09 0.00

G×Y 3 0.17 0.06 0.23 0.87

Error I 12 3.02 0.25

H 3 17.55 5.85 422.36 0.00

H×Y 3 0.04 0.01 0.99 0.40

H×G 9 0.18 0.02 1.46 0.17

H×G×Y 9 0.26 0.03 2.08 0.03

Error II 48 1.55 0.03

N 3 499.91 166.64 5145.93 0.00

N×Y 3 0.16 0.05 1.60 0.20

N×H 9 1.34 0.15 10.71 0.00

N×H×Y 9 0.21 0.02 1.66 0.10

N×G 9 2.43 0.27 8.35 0.00

N×G×Y 9 0.37 0.04 1.27 0.28

N×H×G 27 0.52 0.02 1.39 0.11

N×H×G×Y 27 0.53 0.02 1.42 0.09

Error III 192 2.66 0.01

Total 383 603.40



276

Table 72. Combined statistical analysis of variance for grains row-1 of maize

genotypes as affected by humic acid, nitrogen and genotypes


Year 1 22.62 22.62 11.63 0.04


Genotypes 3 707.60 235.87 113.94 0.00

G×Y 3 4.26 1.42 0.69 0.58

Error I 12 24.84 2.07

H 3 75.12 25.04 1392.16 0.00

H×Y 3 0.02 0.01 0.30 0.83

H×G 9 0.80 0.09 4.91 0.00

H×G×Y 9 0.93 0.10 5.77 0.00

Error II 48 14.91 0.31

N 3 2200.44 733.48 2361.92 0.00

N×Y 3 1.06 0.35 1.13 0.35

N×H 9 1.32 0.15 8.15 0.00

N×H×Y 9 0.15 0.02 0.93 0.50

N×G 9 17.00 1.89 6.08 0.00

N×G×Y 9 2.25 0.25 0.81 0.61

N×H×G 27 2.10 0.08 4.32 0.08

N×H×G×Y 27 0.82 0.03 1.68 0.02

Error III 192 3.45 0.02

Total 383 3087.44



277

Table 73. Combined statistical analysis of variance for grains ear-1 of maize



Year 1 6479.66 6479.66 13.22 0.04

Reps within Y 4 1961.30 490.32

Genotypes 3 326902.17 108967.39 1007.87 0.00

G×Y 3 268.16 89.39 0.83 0.50

Error I 12 1297.40 108.12

H 3 64893.70 21631.23 3475.76 0.00

H×Y 3 181.96 60.65 9.75 0.00

H×G 9 490.85 54.54 8.76 0.00

H×G×Y 9 65.35 7.26 1.17 0.32

Error II 48 777.07 16.19

N 3 1657180.89 552393.63 34121.50 0.00

N×Y 3 193.85 64.62 3.99 0.01

N×H 9 1971.54 219.06 35.20 0.00

N×H×Y 9 64.40 7.16 1.15 0.33

N×G 9 19330.78 2147.86 132.67 0.00

N×G×Y 9 508.69 56.52 3.49 0.00

N×H×G 27 458.41 16.98 2.73 0.00

N×H×G×Y 27 183.83 6.81 1.09 0.35

Error III 192 1194.90 6.22

Total 383 2084404.92



278

Table 74. Combined statistical analysis of variance for thousand grain weight

(g) of maize genotypes as affected by humic acid and nitrogen


Year 1 1324.55 1324.55 16.19 0.03

Reps within Y 4 327.34 81.84

Genotypes 3 356460.16 118820.05 5823.27 0.00

G×Y 3 215.37 71.79 3.52 0.05

Error I 12 244.85 20.40

H 3 2822.58 940.86 1490.89 0.00

H×Y 3 43.17 14.39 22.80 0.00

H×G 9 33.58 3.73 5.91 0.00

H×G×Y 9 5.94 0.66 1.05 0.41

Error II 48 249.19 5.19

N 3 58427.05 19475.68 3751.42 0.00

N×Y 3 240.65 80.22 15.45 0.00

N×H 9 51.03 5.67 8.99 0.00

N×H×Y 9 3.77 0.42 0.66 0.74

N×G 9 234.94 26.10 5.03 0.00

N×G×Y 9 343.20 38.13 7.35 0.00

N×H×G 27 82.69 3.06 4.85 0.00

N×H×G×Y 27 36.33 1.35 2.13 0.00

Error III 192 121.17 0.63

Total 383 421267.57



279

Table 75. Combined statistical analysis of variance for biological yield (kg ha-1)

of maize genotypes as affected by humic acid and nitrogen


Year 1 4248312.76 4248312.76 88.15 0.00

Reps within Y 4 192781.67 48195.42

Genotypes 3 2335868990.06 778622996.69 17092.11 0.00

G×Y 3 60028.97 20009.66 0.44 0.73

Error I 12 546654.25 45554.52

H 3 105320334.25 35106778.08 3898.44 0.00

H×Y 3 1173309.95 391103.32 43.43 0.00

H×G 9 1980973.40 220108.16 24.44 0.00

H×G×Y 9 998832.57 110981.40 12.32 0.00

Error II 48 778962.08 16228.38

N 3 2145464288.19 715154762.73 44068.16 0.00

N×Y 3 2165292.18 721764.06 44.48 0.00

N×H 9 6568798.52 729866.50 81.05 0.00

N×H×Y 9 2676140.28 297348.92 33.02 0.00

N×G 9 121707318.13 13523035.35 833.30 0.00

N×G×Y 9 1358981.68 150997.96 9.30 0.00

N×H×G 27 5194350.42 192383.35 21.36 0.00

N×H×G×Y 27 2060387.95 76310.66 8.47 0.00

Error III 192 1729026.67 9005.35

Total 383 4740093763.96



280

Table 76. Combined statistical analysis of variance for grain yield (kg ha-1) of


SOV DF SS MS F P

Year 1 1949685.01 1949685.01 66.99 0.00

Reps within Y 4 116421.17 29105.29

Genotypes 3 585191388.47 195063796.16 8892.00 0.00

G×Y 3 28104.51 9368.17 0.43 0.74

Error I 12 263244.08 21937.01

H 3 34862748.86 11620916.29 7369.76 0.00

H×Y 3 69672.20 23224.07 14.73 0.00

H×G 9 633676.91 70408.55 44.65 0.00

H×G×Y 9 21968.61 2440.96 1.55 0.13

Error II 48 325709.92 6785.62

N 3 855477796.43 285159265.48 42024.03 0.00

N×Y 3 85709.93 28569.98 4.21 0.01

N×H 9 1761966.28 195774.03 124.16 0.00

N×H×Y 9 47633.70 5292.63 3.36 0.00

N×G 9 49653245.93 5517027.33 813.05 0.00

N×G×Y 9 380819.30 42313.26 6.24 0.00

N×H×G 27 723298.70 26788.84 16.99 0.00

N×H×G×Y 27 64768.41 2398.83 1.52 0.06

Error III 192 302752.83 1576.84

Total 383 1531960611.24



281

Table 77. Combined statistical analysis of variance for stover yield (kg ha-1) of



Year 1 442002.04 442002.04 10.03 0.05

Reps within Y 4 176269.29 44067.32

Genotypes 3 669233327.97 223077775.99 6451.52 0.00

G×Y 3 146246.06 48748.69 1.41 0.29

Error I 12 414930.38 34577.53

H 3 19274288.61 6424762.87 602.00 0.00

H×Y 3 833024.71 277674.90 26.02 0.00

H×G 9 1674328.41 186036.49 17.43 0.00

H×G×Y 9 922345.77 102482.86 9.60 0.00

Error II 48 742108.67 15460.60

N 3 291800790.45 97266930.15 6291.28 0.00

N×Y 3 1719205.37 573068.46 37.07 0.00

N×H 9 1980251.76 220027.97 20.62 0.00

N×H×Y 9 2602067.79 289118.64 27.09 0.00

N×G 9 21243814.74 2360423.86 152.67 0.00

N×G×Y 9 1211843.77 134649.31 8.71 0.00

N×H×G 27 2637423.80 97682.36 9.15 0.00

N×H×G×Y 27 1955324.48 72419.43 6.79 0.00

Error III 192 2049103.67 10672.41

Total 383 1021058697.74



282

Table 78. Combined statistical analysis of variance for harvest index (%) of



Year 1 21.25 21.25 25.58 0.01


Genotypes 3 2663.96 887.99 1798.57 0.00

G×Y 3 5.98 1.99 4.04 0.03

Error I 12 5.92 0.49

H 3 195.24 65.08 518.66 0.00

H×Y 3 2.73 0.91 7.26 0.00

H×G 9 9.70 1.08 8.59 0.00

H×G×Y 9 4.99 0.55 4.42 0.00

Error II 48 10.81 0.23

N 3 6397.45 2132.48 9470.48 0.00

N×Y 3 9.82 3.27 14.54 0.00

N×H 9 36.25 4.03 32.10 0.00

N×H×Y 9 14.91 1.66 13.21 0.00

N×G 9 59.87 6.65 29.54 0.00

N×G×Y 9 14.91 1.66 7.36 0.00

N×H×G 27 10.75 0.40 3.17 0.00

N×H×G×Y 27 10.99 0.41 3.24 0.00

Error III 192 24.09 0.13

Total 383 9502.96



283

Table 79. Combined statistical analysis of variance for NUE-AE (kg grains kg-1

N) of maize genotypes as affected by humic acid and nitrogen


Year 1 0.06 0.06 0.06 0.83


Genotypes 3 4189.51 1396.50 828.25 0.00

G×Y 3 5.61 1.87 1.11 0.38

Error I 12 20.23 1.69

H 3 899.15 299.72 6891.71 0.00

H×Y 3 0.52 0.17 3.96 0.01

H×G 9 21.30 2.37 54.41 0.00

H×G×Y 9 0.74 0.08 1.89 0.06

Error II 48 15.79 0.33

N 3 23539.88 7846.63 23855.93 0.00

N×Y 3 0.06 0.02 0.06 0.98

N×H 9 538.41 59.82 1375.57 0.00

N×H×Y 9 0.77 0.09 1.98 0.04

N×G 9 1415.60 157.29 478.20 0.00

N×G×Y 9 9.24 1.03 3.12 0.00

N×H×G 27 54.02 2.00 46.00 0.00

N×H×G×Y 27 1.64 0.06 1.40 0.10

Error III 192 8.35 0.04

Total 383 30724.76



284

Table 80. Combined statistical analysis of variance for NUE-PFP (kg grains kg-

1 N) of maize genotypes as affected by humic acid and nitrogen

SOV DF SS MS F P

Year 1 30.88 30.88 25.22 0.02


Genotypes 3 14712.61 4904.20 5411.59 0.00

G×Y 3 2.13 0.71 0.78 0.53

Error I 12 10.87 0.91

H 3 899.15 299.72 6891.71 0.00

H×Y 3 0.52 0.17 3.96 0.01

H×G 9 21.30 2.37 54.41 0.00

H×G×Y 9 0.74 0.08 1.89 0.06

Error II 48 11.87 0.25

N 3 120421.70 40140.57 162304.92 0.00

N×Y 3 14.05 4.68 18.94 0.00

N×H 9 538.41 59.82 1375.57 0.00

N×H×Y 9 0.77 0.09 1.98 0.04

N×G 9 5419.50 602.17 2434.81 0.00

N×G×Y 9 9.77 1.09 4.39 0.00

N×H×G 27 54.02 2.00 46.00 0.00

N×H×G×Y 27 1.64 0.06 1.40 0.10

Error III 192 8.35 0.04

Total 383 142163.17



285

Table 81. Combined statistical analysis of variance for NAR (g m-2 day-1) of


SOV DF SS MS F P

Year 1 0.92 0.92 9.95 0.05


Genotypes 3 293.33 97.78 2768.02 0.00

G×Y 3 0.04 0.01 0.40 0.75

Error I 12 0.42 0.04

H 3 5.98 1.99 715.26 0.00

H×Y 3 0.12 0.04 14.49 0.00

H×G 9 0.06 0.01 2.37 0.01

H×G×Y 9 0.06 0.01 2.37 0.01

Error II 48 0.45 0.01

N 3 231.35 77.12 8294.40 0.00

N×Y 3 0.05 0.02 1.73 0.17

N×H 9 0.16 0.02 6.53 0.00

N×H×Y 9 0.01 0.00 0.53 0.85

N×G 9 4.22 0.47 50.42 0.00

N×G×Y 9 0.29 0.03 3.48 0.00

N×H×G 27 0.28 0.01 3.66 0.00

N×H×G×Y 27 0.12 0.00 1.61 0.04

Error III 192 0.53 0.00

Total 383 538.76



286

Table 82. Combined statistical analysis of variance for soil P content (mg kg-1)

at maize harvest as affected by maize genotypes, humic acid and

nitrogen


Year 1 0.57 0.57 161.86 0.00


Genotypes 3 1.84 0.61 101.22 0.00

G×Y 3 0.04 0.01 2.02 0.16

Error I 12 0.07 0.01

H 3 1288.07 429.36 170658.43 0.00

H×Y 3 0.01 0.00 0.80 0.50

H×G 9 0.20 0.02 9.00 0.00

H×G×Y 9 0.02 0.00 0.86 0.56

Error II 48 0.10 0.00

N 3 1.09 0.36 172.16 0.00

N×Y 3 0.01 0.00 1.26 0.30

N×H 9 0.02 0.00 0.78 0.63

N×H×Y 9 0.01 0.00 0.59 0.81

N×G 9 0.01 0.00 0.65 0.75

N×G×Y 9 0.02 0.00 1.29 0.27

N×H×G 27 0.03 0.00 0.46 0.99

N×H×G×Y 27 0.04 0.00 0.62 0.93

Error III 192 0.48 0.00

Total 383 1292.66



287

Table 83. Combined statistical analysis of variance for soil N (%) at maize

harvest as affected by maize genotypes, humic acid and nitrogen

SOV DF SS MS F P

Year 1 0.00012 0.00012 95.92 0.00

Reps within Y 4 0.00001 0.00000

Genotypes 3 0.00170 0.00057 302.34 0.00

G×Y 3 0.00000 0.00000 0.52 0.67

Error I 12 0.00002 0.00000

H 3 0.06553 0.02184 23044.44 0.00

H×Y 3 0.00001 0.00000 4.03 0.01

H×G 9 0.00014 0.00002 15.83 0.00

H×G×Y 9 0.00002 0.00000 2.69 0.01

Error II 48 0.00001 0.00000

N 3 0.00086 0.00029 1002.01 0.00

N×Y 3 0.00000 0.00000 1.42 0.25

N×H 9 0.00001 0.00000 1.16 0.32

N×H×Y 9 0.00001 0.00000 0.78 0.64

N×G 9 0.00000 0.00000 1.02 0.44

N×G×Y 9 0.00000 0.00000 1.00 0.45

N×H×G 27 0.00001 0.00000 0.48 0.99

N×H×G×Y 27 0.00001 0.00000 0.54 0.97

Error III 192 0.00018 0.00000 95.92

Total 383 0.06866



288

Table 84. Combined statistical analysis of variance for grain protein (%) of



Year 1 1.82 1.82 837.25 0.00


Genotypes 3 624.03 208.01 14279.49 0.00

G×Y 3 0.19 0.06 4.24 0.03

Error I 12 0.17 0.01

H 3 13.76 4.59 416.26 0.00

H×Y 3 0.15 0.05 4.53 0.00

H×G 9 0.26 0.03 2.57 0.01

H×G×Y 9 0.07 0.01 0.69 0.72

Error II 48 0.65 0.01

N 3 38.91 12.97 956.99 0.00

N×Y 3 0.02 0.01 0.38 0.77

N×H 9 1.57 0.17 15.86 0.00

N×H×Y 9 0.30 0.03 3.07 0.00

N×G 9 2.55 0.28 20.93 0.00

N×G×Y 9 0.16 0.02 1.27 0.28

N×H×G 27 0.55 0.02 1.86 0.01

N×H×G×Y 27 0.39 0.01 1.32 0.14

Error III 192 2.12 0.01

Total 383 687.67



289

Table 85. Combined statistical analysis of variance for soil organic matter (%)

at maize harvest as affected by maize genotypes, humic acid and

nitrogen


Year 1 0.2157 0.2157 104.51 0.00

Reps within Y 4 0.0083 0.0021

Genotypes 3 0.1355 0.0452 73.26 0.00

G×Y 3 0.0036 0.0012 1.96 0.17

Error I 12 0.0074 0.0006

H 3 47.4693 15.8231 80018.42 0.00

H×Y 3 0.1022 0.0341 172.28 0.00

H×G 9 0.0648 0.0072 36.39 0.00

H×G×Y 9 0.1427 0.0159 80.19 0.00

Error II 48 0.0069 0.0001

N 3 0.0747 0.0249 172.89 0.00

N×Y 3 0.0010 0.0003 2.29 0.09

N×H 9 0.0144 0.0016 8.09 0.00

N×H×Y 9 0.0009 0.0001 0.50 0.87

N×G 9 0.0015 0.0002 1.18 0.33

N×G×Y 9 0.0030 0.0003 2.32 0.03

N×H×G 27 0.0053 0.0002 0.99 0.49

N×H×G×Y 27 0.0053 0.0002 0.99 0.49

Error III 192 0.0380 0.0002

Total 383 48.3003



integration of humic acid with nitrogen for improving yield of ...

Documents

Transcript of integration of humic acid with nitrogen for improving yield of ...