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Rapid and Inexpensive Steam Distillation Method for Routine Analysis ofInorganic Nitrogen in Alkaline Calcareous SoilsMuhammad Akhtara; F. Hussaina; T. M. Qureshia; M. Y. Ashrafa; J. Akhtera; A. Haqa

a Nuclear Institute for Agriculture and Biology (NIAB), Jhang Road, Faisalabad, Pakistan

Online publication date: 05 April 2011

To cite this Article Akhtar, Muhammad , Hussain, F. , Qureshi, T. M. , Ashraf, M. Y. , Akhter, J. and Haq, A.(2011) 'Rapidand Inexpensive Steam Distillation Method for Routine Analysis of Inorganic Nitrogen in Alkaline Calcareous Soils',Communications in Soil Science and Plant Analysis, 42: 8, 920 — 931To link to this Article: DOI: 10.1080/00103624.2011.558961URL: http://dx.doi.org/10.1080/00103624.2011.558961

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Communications in Soil Science and Plant Analysis, 42:920–931, 2011Copyright © Taylor & Francis Group, LLCISSN: 0010-3624 print / 1532-2416 onlineDOI: 10.1080/00103624.2011.558961

Rapid and Inexpensive Steam Distillation Methodfor Routine Analysis of Inorganic Nitrogen in

Alkaline Calcareous Soils

MUHAMMAD AKHTAR, F. HUSSAIN, T. M. QURESHI,M. Y. ASHRAF, J. AKHTER, AND A. HAQ

Nuclear Institute for Agriculture and Biology (NIAB), Jhang Road, Faisalabad,Pakistan

Determination of inorganic nitrogen (N) in soil is important in making N fertilizerrecommendations for crops. To find a rapid, reliable, and economical method for theestimation of inorganic N in alkaline calcareous soils of Pakistan, three steam distil-lation methods were compared using soils varying in ammonium (NH4) and nitrate(NO3) N contents and other physicochemical properties. In the standard method, thesoil sample is shaken with 2 N potassium chloride (KCl) for 1 h, and the extract is thenanalyzed by steam distillation. In the other two methods, the soil sample is distilleddirectly with either 2 N KCl or distilled/deionized water. Based on the results of thepresent work, a method that involves steam distillation with only distilled/deionizedwater and that requires half the quantity of magnesium oxide (MgO) of the standardmethod has been proposed, as all the three methods yielded identical results for NH4-and NO3-N contents. Being economical, the proposed method for inorganic N estima-tion by direct distillation of soil with distilled/deionized water deserves considerationfor adoption by soil-testing laboratories.

Keywords Inorganic nitrogen, repaid N determination, NH4- and NO3-N and soilanalysis

Introduction

Inorganic/mineral nitrogen [ammonium (NH4) + nitrate (NO3)] is an important compo-nent of soil fertility as it is readily plant available and used as an aid in predicting nitrogen(N) fertilizer needs of crop because of more ease in determination (Zhang et al. 2002;Hussain, Malik, and Naqvi 1994; Gianello and Bremner 1986; Keeney and Nelson 1982).Recently, fertilization-based environmental pollution and economical crop production havenecessitated the determination of soil N for rational use of N fertilizers (Wilson andBall 1999).

Determination of soil N in Pakistan was initiated in the 1970s to assess the fertilizer Nrequirement of wheat (Quddus, Siddiq, and Riaz 2008). Thereafter, several biological andchemical methods have been proposed for estimating mineral N in soil (Bremner 1965).The chemical methods became popular because the procedures are simpler and they takeless time. Generally, they involve shaking of the samples with salt solutions, filtration,

Received 17 August 2009; accepted 16 November 2010.Address correspondence to M. Y. Ashraf, Nuclear Institute for Agriculture and Biology (NIAB),

Jhang Road, Faisalabad, Pakistan. E-mail: niabmyashraf@hotmail.com

920

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Rapid Analysis of Inorganic Nitrogen 921

and distillation (Keeney and Nelson 1982). Of the chemical methods, the method involv-ing steam distillation has been widely adopted for the determination of NH4- and NO3-N.It was described in detail by Bremner (1965), evaluated in many studies (Bremner andKeeney 1965, 1966; Bremner and Edwards 1965), and widely adopted as standard proce-dure for determining soil N. Soon, its practical usefulness was lost because it consumed alot of time and chemicals to determine N in soil samples. Therefore, attempts have beenmade to introduce rapid and simple procedures to assess the soil N supply and providetimely advice to farmers for fertilization of their fields to ameliorate deficient N and meetthe crop requirement (Kmecl, Sudin, and Zupancic-Kralj 2005; Keeney and Bremner 1966;Curtin et al. 2005).

The purpose of this study was to establish a simple, rapid, and reliable techniquefor the determination of the soil N to enhance the usefulness and practical implication ofN-determination procedures. In comparison with the existing procedures, a simple proce-dure of the N determination was evaluated that involved direct distillation of the soil–watermixture [without potassium chloride (KCl) addition] while keeping the reliability of themethodology. Hence, the concepts behind all efforts were simplicity and economy withoutlosing precision in the determination of soil mineral N contents.

Materials and Methods

The soils used were collected from 23 different locations in Punjab Province of Pakistancultivated for the production of cereal crops in a rice–wheat rotation system. Soil sampleswere collected from the 0- to 15-cm depth from all the sites. The samples were air dried,ground to pass through a 2-mm sieve, and analyzed for pH and electrical conductivity (EC)(Rhoades 1982), calcium carbonate (CaCO3) (Puri 1931), texture (Bouyoucos 1927), andorganic-matter content (Walkley and Black 1934) (Table 1).

Evaluation of Methods for the Determination of NH4- and NO3-N in Soil

Two steam distillation procedures described by Keeney and Nelson (1982) and one mod-ified by this laboratory were used to determine NH4- and NO3-N contents in 20 soilsamples. The soil analysis was carried out on quadruplicate samples, and the resultsobtained by these three methods were compared to evaluate the modified procedure incomparison with the existing steam distillation procedures. The details of these threeprocedures are given here:

Standard Method (M1). The residual NO3- and NH4-N were determined by adding 10 gof soil and 100 mL of 2 N KCl to a plastic vial that was closed with a screw stopper.The samples were then shaken for 1 h, and the suspension was allowed to settle downfor half an hour. The analysis was performed on the aliquot directly or after filtrationof the suspension if the analysis was delayed for more than 24 h (Keeney and Nelson1982).

Direct Distillation with 2 N KCl (M2). The standard method (M1) was later modified byKeeney and Bremner (1982). The procedure involves direct distillation of the 2 N KCl +soil mixture to obtain the distillate and analyze for mineral N. This procedure eliminatesthe step of shaking and extraction.

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Tabl

e1

Som

eph

ysic

alan

dch

emic

alpr

oper

ties

ofso

ilsus

edfo

rth

est

udie

s

Soil

no.

Loc

atio

n/di

stri

ctpH

s

EC

e

(dS

m−1

)C

aCO

3

(%)

OM

(%)

Tota

lN

(%)

Cla

y(%

)Si

lt(%

)Sa

nd(%

)Te

xtur

e

1Fa

isal

abad

7.7

1.90

6.6

0.57

0.04

222

.518

.159

.4Sa

ndy

clay

loam

2To

ba7.

42.

547.

50.

770.

056

26.7

27.7

45.6

Loa

my

clay

3Sa

hiw

al7.

61.

596.

00.

960.

069

16.2

23.5

60.3

Sand

ycl

aylo

am4

Veh

ari

7.8

8.9

9.5

1.17

0.07

824

.434

.740

.9C

lay

loam

5M

.Gha

rh7.

79.

010

.51.

120.

071

29.3

40.8

29.9

Silty

clay

6Jh

ang

7.8

11.0

9.5

0.80

0.05

323

.022

.254

.8Sa

ndy

clay

loam

7Sa

rgod

ha7.

43.

955.

41.

460.

097

24.4

24.2

51.4

Cla

ylo

am8

Guj

rat

7.4

0.60

2.4

1.58

0.10

745

.424

.829

.8C

lay

9Je

hlum

7.7

0.35

2.3

0.61

0.04

112

.413

.674

.0Sa

ndy

loam

10R

awal

pind

i7.

50.

3512

.30.

910.

064

24.8

31.0

44.2

Cla

ylo

am11

Mur

ree

7.4

0.42

5.0

2.40

0.11

231

.418

.050

.6L

oam

ycl

ay12

Sial

kot

7.7

0.72

3.0

0.73

0.12

842

.236

.821

.0L

oam

ycl

ay13

Guj

ranw

ala

7.6

0.83

2.2

1.14

0.07

119

.022

.059

.0Sa

ndy

clay

loam

14L

ahor

e7.

60.

805.

51.

330.

081

24.2

19.8

56.0

Sand

ycl

aylo

am15

Qas

oor

7.7

1.81

8.4

1.25

0.08

436

.634

.429

.0L

oam

ycl

ay16

Fais

alab

ad(f

ruit

orch

ard)

7.6

0.80

4.7

3.35

0.17

119

.425

.455

.2Sa

ndy

clay

loam

17Fa

isal

abad

(flow

ernu

rser

y)

7.4

1.00

4.6

2.44

0.14

021

.829

.049

.2C

lay

loam

922

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18Fa

isal

abad

(lon

g-st

ored

soil)

7.7

0.54

1.8

1.10

0.06

924

.822

.652

.6C

lay

loam

19Fa

isal

abad

(lon

g-st

ored

soil)

7.7

0.78

1.8

0.86

0.05

924

.822

.652

.6C

lay

loam

20Fa

isal

abad

(lon

g-st

ored

soil)

7.9

0.76

2.1

1.19

0.05

524

.822

.652

.6C

lay

loam

21M

ulta

n7.

81.

196.

81.

890.

113

29.8

34.0

36.2

Loa

my

clay

22R

awal

pind

i7.

50.

402.

21.

230.

090

21.4

33.4

45.2

Cla

ylo

am23

Sial

kot

7.7

1.21

3.2

1.76

0.11

836

.624

.439

.0L

oam

ycl

ay

Not

es.E

Ce,

elec

tric

alco

nduc

tivity

ofsa

tura

tion

extr

act;

OM

,org

anic

mat

ter.

923

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924 M. Akhtar et al.

Direct Distillation with Distilled/Deionized Water (M3). The procedure proposed bythis laboratory involves the direct distillation of soil simply with distilled/deionizedwater to collect the distillate for N determination. This eliminates KCl consumption andshaking/extraction of the sample, and moreover it requires half the amount of magnesiumoxide (MgO) during distillation to yield the same results.

The modification in the standard procedure (M1) was made to eliminate the nonessen-tial steps during the N determination as given in Table 2.

The validity of the proposed method (M3) of N determination was examined by deter-mining N from soils varying in native N contents and also from soils that were enrichedwith NH4-N and thus had variable levels of exchangeable NH4-N. To validate the method,the accuracy and the reproducibility/precision of the results were determined.

Comparison of the Methods using Linear Regression

A comparison using a linear regression curve was produced by analyzing 10 soils contain-ing ranges of NH4-N (5.82–86.85 mg kg−1 soil) and NO3-N (4.6–67.45 mg kg−1 soil) toobtain correlation of the standard (M1), modified (M2), and proposed method (M3) of Ndetermination. Linear regression is a preferred statistical method when a new analyticalmethod is compared with a standard method (Miller and Miller 1993). Linear regressionswere made among the results of standard, modified, and proposed methods. In this case,the null hypothesis followed that the intercept differed significantly from zero and the slopediffered significantly from 1.

Confirmatory Test for Reliability of the Modified Methods

Two tests were carried out to confirm precision and reproducibility of the proposed method(M3) along with existing methods of the N determinations. Five soils with wide variationin physicochemical properties were selected out of the used soils.

Test 1. Generally, the determination of the exchangeable NH4 requires shaking of soil with2 N KCl to replace NH4 ions. The utility of the proposed method (M3) was judged byemploying all the three methods (M1, M2, and M3) to displace the exchangeable NH4-Ncontents of soil. The soils were saturated with exchangeable NH4-N by passing 1 N ammo-nium acetate solution and later by washing with ethyl alcohol to remove the soluble NH4.The confirmation of the utility of the M3 method was evaluated by comparing its resultswith those obtained by M1 and M2.

Table 2Comparison of chemicals consumed and other steps involved in procedures M1, M2, and

M3 for the determination of NO3- and NH4-N

MethodsKCl 2 N(20 ml)

MgO(0.2 g)

Devardaalloy (0.2 g) Shaking Extraction Distillation

M1 Yes Yes Yes Yes Yes YesM2 Yes Yes Yes No No YesM3 No Half (0.1 g) Yes No No Yes

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Rapid Analysis of Inorganic Nitrogen 925

Test 2. During this test, a 50-g sample of selected soils (in triplicate) were incubated inplastic bottles at field capacity after supplementing with 200 mg N kg−1 as ammonium sul-fate [(NH4)2SO4]. The bottles were covered with stoppers and then placed in an incubatorat 30 ± 2 ◦C. Deficient water contents were replenished daily. Three days after incubation,NH4- and NO3-N contents were determined using these procedures.

The values obtained by the standard method (M1) were considered as real while thoseobtained by the proposed method (M3) were considered as experimental. Therefore, mea-surements of accuracy, precision, and reliability of the proposed method were performed.

Statistical Analysis

The data were subjected to the analysis of variance to assess significance of the measure-ments through different analytical methods. Means were compared by using the student’st-test (P ≤ 0.05). To assess precision and reproducibility, coefficients of variation (CVs)were calculated, and lower values were considered as indicators of good precision (Jimenezand Ladha 1993; Lowther et al. 1990). The CV may be preferred over standard deviation(SD) values for making decisions about the precision of analytical procedures determiningthe same analyte concentrations. The CV is a standardization of the SD that allows com-parison of variability estimates through a wide range of analyte concentrations. The CVis defined as the SD divided by the mean and is multiplied by 100 to report the results inpercentage (George, Lynn, and Bruce 2002).

Results and Discussion

The data in Table 3 show the contents of NH4- and NO3-N of 20 soils using all the threemethods: (a) standard method (M1), (b) direct 2 N KCl distillation (M2), and (c) directdistillation with distilled/deionized water (M3).

Validation of the Proposed N Tests

The NH4- and NO3-N contents of the soils determined by both methods were found tobe statistically similar (P < 0.05), showing that the modified/proposed methods (M2 andM3) are as accurate as the standard method (M1). The results suggested that the eitherprocedure could be employed for the determination of the mineral soil N content. Theproposed method (M3) is also found to be as efficient as the modified (M2) and standard(M1) methods in determining the N contents of soil (Table 3). The method (M3) offers theadvantages of low energy and chemical consumption while maintaining the precision andreproducibility of the analysis.

Reproducibility of different procedures measuring the same quantity has been judgedby the scientists using CV values, which indicate the possible disparity between theirresults (George, Lynn, and Bruce 2002). The results of the present study showed lowervalues of CVs (0.9–2.31) for the results of replicated samples carried out under the sameset of conditions. The mean CVs (%) of methods M1, M2, and M3 were 1.83, 1.97, and2.31 for NH4-N and 0.97, 1.02, and 1.87 for NO3-N determination (Table 3), respectively,which were small enough to validate the precision/reproducibility of the results. Danielet al. (2001) compared two methods for soil carbon and nitrogen determination and showedthat a value of CV of 3.82% was an acceptable value to validate the reproducibility of themethods. Other scientists also suggested that the smaller values of CV [1.6–2.8% foundby Jimenez and Ladha (1993) and 0.2–0.8% found by Kmecl, Sudin, and Zupancic-Kralj(2005)] could be used as an indicator for good reproducibility and precision of the results

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Tabl

e3

Inor

gani

cN

cont

ents

(mg

kg−1

)in

20so

ilsas

dete

rmin

edby

thre

est

eam

dist

illat

ion

proc

edur

es:M

1(s

tand

ard)

,M2

(dir

ect2

NK

Cl)

,an

dM

3(d

irec

tdei

oniz

edw

ater

)

NH

4-N

NO

3-N

M1

M2

M3

M1

M2

M3

Soil

no.

mg

kg−1

SDm

gkg

−1SD

mg

kg−1

SDm

gkg

−1SD

mg

kg−1

SDm

gkg

−1SD

16.

650.

405.

820.

677.

000.

5745

.90

0.99

46.8

00.

5745

.50

0.99

211

.72

0.35

10.5

50.

9012

.25

1.21

28.7

52.

1628

.95

1.67

28.7

00.

573

7.70

0.99

6.70

0.80

7.52

0.35

36.9

71.

4437

.00

0.57

37.1

00.

994

9.97

1.05

9.67

0.67

10.8

50.

4063

.22

0.67

62.3

00.

3562

.65

1.34

56.

650.

707.

051.

347.

000.

5743

.80

0.57

43.6

51.

3543

.57

1.19

68.

051.

217.

400.

998.

051.

3426

.82

0.67

27.9

01.

3426

.25

1.34

78.

751.

348.

270.

359.

270.

6766

.90

0.99

67.4

50.

0067

.55

1.76

812

.60

0.80

13.0

00.

0014

.35

0.70

17.7

20.

6716

.97

1.34

17.6

70.

679

7.17

0.35

7.75

0.70

6.47

0.35

4.60

1.27

4.37

0.70

4.02

0.80

109.

620.

678.

970.

678.

570.

674.

600.

804.

720.

804.

550.

5711

11.3

70.

6710

.90

0.57

11.3

70.

8810

.37

0.67

11.2

70.

4011

.72

1.32

1217

.50

0.00

17.7

20.

6717

.85

0.40

8.45

0.70

7.92

0.67

9.80

1.40

139.

100.

007.

400.

577.

870.

8811

.60

0.00

11.2

70.

8810

.85

1.34

149.

800.

579.

670.

6710

.15

0.90

6.70

0.00

6.55

0.35

6.30

0.80

1511

.37

0.67

11.0

70.

6711

.20

0.80

11.7

70.

6711

.27

0.70

10.8

51.

2116

19.9

50.

4019

.65

0.90

19.0

71.

1915

.80

0.99

14.8

70.

3515

.92

0.67

1716

.62

0.35

16.8

50.

7018

.02

1.19

44.3

20.

8844

.45

0.99

42.8

71.

0518

52.1

50.

7052

.72

0.05

52.5

00.

005.

651.

344.

720.

904.

900.

8019

36.9

21.

0536

.27

0.88

36.9

21.

1910

.37

0.88

11.2

70.

4910

.85

0.70

2086

.80

0.80

86.8

50.

7087

.50

0.00

6.35

0.70

6.55

1.05

7.35

0.70

Mea

n18

.02

0.33

17.7

10.

3518

.19

0.42

23.5

30.

2323

.51

0.24

23.4

50.

44C

V(%

)1.

831.

972.

310.

971.

021.

87

Not

es.E

ntri

esin

aco

lum

nar

em

eans

offo

urre

plic

ates

.M1,

M2,

and

M3

are

stan

dard

,dir

ect2

NK

Cl,

and

dire

ctde

ioni

zed

wat

erdi

still

atio

nm

etho

dsof

inor

gani

cN

dete

rmin

atio

n,re

spec

tivel

y.

926

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Rapid Analysis of Inorganic Nitrogen 927

obtained from different methods. As the results achieved by all the three methods producedlittle variability, the proposed method (M3) could be considered as precise and reproducibleas the existing procedures (M1 and M2) and could be used as an alternative for routineanalysis of inorganic N.

Miller and Miller (1993) proposed that a linear regression was the preferred statisticalmethod when a new analytical method is compared with standard procedure. The results ofNH4-N (Figures 1–3) and NO3-N contents (Figures 4–6) obtained by the standard method(M1) correlated well (R2 ≥ 0.99) with the results of direct 2 N KCl (M2) and direct deion-ized water (M3) distillation methods, and also good correlation (R2 ≥ 0.99) was foundbetween methods M2 and M3. The excellent correlation of the proposed method (M3)with the other ones advocates its superiority for estimation of the inorganic N because ofits lower consumption of energy, cost, and labor. A good correlation (R2 ≥ 0.98) betweendifferent methods for N determination has been shown by the scientists for validation ofthe results (Kmecl, Sudin, and Zupancic-Kralj 2005). Jeferson et al. (2007) used the con-cept of correlation for comparing two methods of N determination and considered highercorrelation (R2 ≥ 0.98) as an indicator for validation of the results. Daniel et al. (2001)used the simple linear regression with the confidence intervals for the intercept and slopeto compare two analytical methods for N determination. They found that a good correlation

y = 1.0029x – 0.1134R2 = 0.9996

0

20

40

60

80

100

0 20 40 60 80 100NH4 - N (mg kg–1 soil) by standard method

NH

4 -

N (

mg

kg–1

soi

l) by

dire

ct K

Cl d

istil

latio

n

Figure 1. Correlation between the values of NH4-N determined using standard and direct 2 N KCldistillation methods.

y = 1.0056x + 0.0635R2 = 0.9992

0

20

40

60

80

100

0 20 40 60 80 100NH4 - N (mg kg–1 soil) by standard method

NH

4 -

N (

mg

kg–1

soi

l) by

DD

Wdi

still

atio

n

Figure 2. Correlation between the values of NH4-N determined using standard and direct deionizedwater (DDW) distillation methods.

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928 M. Akhtar et al.

y = 1.0025x + 0.184

0

20

40

60

80

100

0 20 40 60 80 100NH4 - N (mg kg–1 soil) by direct KCl distillation

NH

4 -

N (

mg

kg–1

soi

l) by

DD

Wdi

still

atio

nR2 = 0.9991

Figure 3. Correlation between the values of NH4-N determined using direct 2 N KCl distillationand direct deionized water (DDW) distillation methods.

y = 1.0123x – 0.6161

0

20

40

60

80

100

0 20 40 60 80 100NO

3 -

N (

mg

kg–1

soi

l) by

dire

ctK

CI d

istil

latio

n

NO3 - N (mg kg–1 soil) by standard method

R2 = 0.9993

Figure 4. Correlation between the values of NO3-N determined using standard and direct 2 N KCldistillation methods.

y = 1.0037x – 0.4462

0

20

40

60

80

100

0 20 40 60 80 100

NO

3 -

N (

mg

kg–1

soi

l) by

DD

W d

istil

latio

n

NO3 - N (mg kg–1 soil) by standard method

R2 = 0.9993

Figure 5. Correlation between the values of NO3-N determined using standard and direct deionizedwater (DDW) distillation methods.

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Rapid Analysis of Inorganic Nitrogen 929

y = 0.991x + 0.182

0

20

40

60

80

100

0 20 40 60 80 100

NO

3 -

N (

mg

kg–1

soi

l) by

DD

Wdi

still

atio

n

NO3 - N (mg kg–1 soil) by direct KCI distillation

R2 = 0.9989

Figure 6. Correlation between the values of NO3-N determined using direct 2 N KCl distillationand direct deionized water (DDW) distillation methods.

coefficient (R2 ≥ 0.95), narrow zero intercept value, and near unity slope value were goodindicators for comparing different analytical methods. The present results (Figures 1–6)yielded acceptable correlation coefficient, near unity slope, and narrow intercept values,which showed the validity of all the three methods: M1, M2, and M3.

Confirmatory tests were conducted to remove the exchangeable NH4-N and addedNH4- and NO3-N using the standard (M1), modified (M2), and proposed methods (M3)as shown in Tables 4 and 5. In general, the deviations among the results obtained by thestandard and the modified methods are extremely small for exchangeable NH4-N and therecovery of added NH4-N and NO3-N. All the three methods produced statistically similarresults for removing the exchangeable NH4-N, native or applied, and also NO3-N, eithernative or formed from applied NH4-N as (NH4)2SO4.

Table 4Exchangeable NH4-N content (%) in soils saturated with NH4 and as determined by three

steam distillation procedures: M1 (standard), M2 (direct 2 N KCl), andM3 (direct deionized water)

Exchangeable NH4-N

Soil no. M1 M2 M3

1 0.030 0.030 0.03121 0.084 0.085 0.0855 0.095 0.095 0.095

22 0.158 0.158 0.15923 0.178 0.179 0.180Mean 0.109 0.109 0.110

Notes. Entries in a column are means of four replicates. M1, M2, and M3 are standard, direct 2 NKCl, and direct deionized water distillation methods of N determination.

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930 M. Akhtar et al.

Table 5Inorganic N contents (mg kg−1) in soils after 3 days of incubation as determined by three

steam distillation procedures: M1 (standard), M2 (direct 2 N KCl), andM3 (direct deionized water)

NH4-N NO3-N

Soil no. M1 M2 M3 M1 M2 M3

1 185.97 185.73 185.97 60.90 60.90 59.9621 224.93 226.10 225.40 17.26 18.66 19.835 199.26 200.90 201.60 44.80 46.90 46.40

22 147.00 150.27 150.73 19.60 21.00 21.4723 221.20 220.03 222.37 16.33 18.66 18.90Mean 195.67 196.60 197.21 31.78 33.22 33.32

Notes. Entries in a column are means of four replicates. M1, M2, and M3 are standard, direct 2 NKCl, and direct deionized water distillation methods of inorganic N determination, respectively.

The data in the tables showed that the proposed method of N determination was asreliable as the standard one in estimating a wide range of NH4-N and NO3-N in alka-line calcareous soils. There were statistically nonsignificant differences in the results forNH4-N and NO3-N estimated by the standard (M1) and modified/proposed methods (M2and M3). The proposed method (M3) requires smaller quantities of chemicals and less timefor analysis as it omits the steps of shaking and filtration (Table 2).

Benefits of the Proposed Method for Inorganic N Determination

The M3 method has a number of advantages over the standard one in terms of economyand rapidity. Use of direct distilled/deionized water decreases the cost, the amount of MgOused is half of that required for the standard procedure, and energy and time are saved byomitting the steps of shaking and filtration.

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