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PHENOLOGY, GROWTH, AND GRAIN YIELD OF MAIZE ASINFLUENCED BY FOLIAR APPLIED UREA AT DIFFERENT GROWTHSTAGESAmanullah a; Muhammad Yasir a; Shad Khan Khalil a; Muhammad Tariq Jan a; Amir Zaman Khan a

a Department of Agronomy, Faculty of Crop Production Sciences, NWFP Agricultural University,Peshawar, Pakistan

Online publication date: 07 December 2009

To cite this Article Amanullah, Yasir, Muhammad, Khalil, Shad Khan, Jan, Muhammad Tariq and Khan, AmirZaman(2010) 'PHENOLOGY, GROWTH, AND GRAIN YIELD OF MAIZE AS INFLUENCED BY FOLIAR APPLIEDUREA AT DIFFERENT GROWTH STAGES', Journal of Plant Nutrition, 33: 1, 71 — 79To link to this Article: DOI: 10.1080/01904160903391099URL: http://dx.doi.org/10.1080/01904160903391099

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Journal of Plant Nutrition, 33:71–79, 2010Copyright C© Taylor & Francis Group, LLC.ISSN: 0190-4167 print / 1532-4087 onlineDOI: 10.1080/01904160903391099

PHENOLOGY, GROWTH, AND GRAIN YIELD OF MAIZE

AS INFLUENCED BY FOLIAR APPLIED UREA

AT DIFFERENT GROWTH STAGES

Amanullah, Muhammad Yasir, Shad Khan Khalil, Muhammad Tariq Jan,

and Amir Zaman Khan � Department of Agronomy, Faculty of Crop ProductionSciences, NWFP Agricultural University, Peshawar, Pakistan

� Foliar urea application is considered an important factor affecting phenology, growth, yield, andyield components of maize. A field experiment was conducted to study effects of urea spray on Azamvariety of maize (Zea mays L.) in Mardan district of the North West Frontier Province (NWFP)of Pakistan during 2005–06. The 5 × 4 factorial experiment was designed with five urea levels(U0 = control, U1 = 2, U2 = 4, U3 = 6 and U4 = 8% urea) applied to main plots and fourapplication timings (T1 = at V9, T2 = V12, T3 = VT and T4 = R1 stages) assigned to subplots.Days to tasseling, silking, and maturity were delayed significantly when urea was applied at the rateof 6% and when applied at the V12 stage. Earlier tasseling, silking, and maturity were observed inurea control plots and in plots that received urea at the V9 stage. Plant height, leaf area, number ofgrains per cob and per line as well as (1000) grain weight, and grain and stover yields increasedsignificantly up to the 6% urea level. Maize yield and yield components were higher when urea wasapplied at the V12 and VT stages than at the V9 and R1 stages. It is concluded that urea spray atthe rate of 6% during the V12 stage would improve the grain yield and yield components of maizein the study area and contribute significantly to increased production.

Keywords: maize, yield, yield components, foliar urea

INTRODUCTION

Several potential benefits of providing nitrogen (N) to cereals via thefoliage as urea solution include reduced N losses through denitrificationand leaching compared with N applications to the soil the ability to provideN when root activity is impaired, e.g., in saline or dry conditions, and uptakelate in the season to increase grain N concentration. Foliar urea applica-tions have increased grain yield, particularly when applied before flag leaf

Received 20 February 2008; accepted 25 January 2009.Address correspondence to Dr. Amanullah, Department of Agronomy, Faculty of Crop Produc-

tion Sciences, NWFP Agricultural University, Peshawar 25130, Pakistan. E-mail: draman agronomist@yahoo.com

71

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72 Amanullah et al.

emergence and when N availability was limiting (Gooding and Davies, 1992).Applications of N near flowering increased post flowering N uptake, grainprotein content, and grain protein concentration (Banziger et al., 1994).Increases in grain N content were often larger when applications of N fertil-izers to the soil were reduced, and when the urea solution was sprayed eitherat anthesis or during the following two weeks (Gooding and Davies, 1992). Asupplemental dose of 7 kg N ha−1 as urea spray significantly increased maizegrain yield (Singh et al., 2005). Compared with soil N application neitherfoliar spray nor injection through the ear affected grain yield or stover drymatter of maize (Ma et al., 2004). Grain and stover yields were unaffected bythe spray treatment apparently because plants were unable to utilize the ureaN applied to the vegetation (primarily leaves) after anthesis to enhance orextend the accumulation of dry matter by either eared or earless plants (Be-low et al., 1985). Foliar applications of urea to chlorotic leaves of N-deficientmaize restored both normal chlorophyll content and stomatal behavior ofleaves (Shimshi, 1967). Increases in N levels significantly increased plantheight, ear length, and diameter, number of kernel row−1 and seed weight(Douby et al., 2000). Grain weight per ear and total grain weight increasedwith an increase in N rate at high density (Gokmen et al., 2001). Applicationof half N as basal and half N as foliar spray at growth stage 3 increased thegrain yield of maize by 43 percent compared to that obtained by applyingfull N (100 kg N ha−1) as basal dose but foliar spray without basal N reducedthe yield of maize by 15 percent compared to normal practices (Islam et al.,1996). Foliar N significantly increased plant height, while days to tasselingand maturity decreased with decreasing level of N (Karim et al., 1983). Grainand stover yields, number of grains per ear, 1000-seed weight, and grainweight per ear increased significantly up to 6% N (Sanjeev et al., 1997).Late season foliar N application had a significant effect on maize yield, totalgrain N, straw yield and total straw N (Woolfolk et al., 2002). Urea sprays didnot increase N content in leaves but decreased the accumulation of carbo-hydrates in stalks and appeared to interfere with indigenous N metabolism.These observations explain the general ineffectiveness of foliar-N treatmentsof maize (Below et al., 1984). The amount of injury by foliar N is modified byadditions of sugar, calcium hydroxide, and potassium bicarbonate. Yield re-sponse of corn to foliar applied N is no greater than to the same amount of Napplied as a side dressing. When injury occurs the yield response is reduced.Ammonia or nitrites did not appear to cause the injury but some product ora number of products of ammonia metabolism did. The beneficial effect ofsucrose is believed to be due to the decreased rate of urea absorption andan increased rate of its translocation within the plant (Foy et al., 1953).

Studies on the proper combination of levels and timings of urea sprayin the agro-ecological maize growing zones of the NWFP, Pakistan havenot been carried out. To exploit the full potential benefits of foliar ureaapplication to maize, more needs to be known about the mechanisms, and

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Maize Response to Urea Spray 73

thus how to prevent losses of N from the foliage, and to reduce the phototoxicinfluences of sprays. The present study was, therefore, initiated to determinethe best level and timing of foliar application of urea on maize to increaseyield and maximize the net income of the farmers.

MATERIAL AND METHODS

Site Description

Experiments were conducted at the Jamra Seed Production and Demon-stration Farm, Takhtbhai Mardan (34.05 to 34.32◦N: 71.48 to 72.25◦E),Pakistan during 2005–06. The farm is located at an altitude of 350 to 400 mabove sea level about 1600 km north of the Indian Ocean with a continen-tal climate. Mean annual rainfall in the region varies from 300 to 400 mm,of which 60–70% occurs in summer (July to September) called monsoon,and 30–40% in winter (December to February). Mean annual temperatureranges from a minimum of 2◦C (January) to a maximum of 45◦C (June). Soilphysio-chemical properties such as soil texture, organic matter, ammoniumbicarbonate (AB)-diethylenetriaminepentaacetic acid (DTPA) extractablephosphorus and exchangeable potassium were determined using standardprocedures (Gee and Bauder, 1986; Nelson and Sommers, 1982; Soltanpour,1985). The soil was calcareous clay loam, low in organic matter (0.60%), ex-tractable phosphorus (P; 4.41 mg kg−1), exchangeable potassium (K; 98 mgkg−1), and alkaline (pH 8.0).

Experimentation

A 5 × 4 factorial experiment was conducted in randomized completeblock (RCB) design with split-plot arrangement using three replications.The treatments comprised five urea levels (U0 = control, U1 = 2, U2 = 4, U3

= 6 and U4 = 8% urea) applied to main plots and four application timings[T1 = at V9 stage (many ear shoots were easily visible upon dissection); T2 =at V12 stage (ear shoots were formed just before tassel formation); T3 = atVT stage (last branch of the tassel was completely visible and the silks werenot yet emerged); and T4 = R1 stage (silks were visible outside the husks)assigned to subplots]. There were 20 subplots in each replication. The sizeof each subplot was 21 m2. Each subplot consisted of 6 rows, 5 m long withrow to row distance of 70 cm and plant to plant distance of 20 cm. A basaldoze of N, phosphorus, and potash was applied at the rate of 60 kg perhectare each during seed bed preparations as urea (46% N), single superphosphate (18% P2O5), and sulfate of potash (50% K2O), respectively. TheAzam variety of maize was used in the experiment. Hoeing was done twice tokeep the crop free of weeds. All the routine agronomic practices were doneuniformly for the entire experimental units. Days to tasseling, silking and

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74 Amanullah et al.

maturity were recorded, and data on plant height (cm), average leaf area(cm2), number of grains per cob and per line, 1000-grain weight, and grainand stover yields were collected.

Data on days to tasseling was recorded when more than 50% of plantsin each treatment developed tassels. Days were counted from date of emer-gence till the completion of more than 50% tasseling. Data on days to silkingwas recorded when more than 50% of plants in each treatment developedsilks. Days were counted form date of emergence till the completion of morethan 50% silking. Number of days to maturity was counted from sowing tillthe plants were fully matured. Plant height was taken from base to top of 10 se-lected plants from each subplot and then averaged. Leaf area was determinedfrom 10 randomly selected plants per treatment by measuring the length andwidth of five middle leaves with a measuring tape and then calculated usingthe formula: Leaf area = Leaf L × Leaf W × 0.75 (Amanullah et al., 2009).

From each treatment ten cobs were selected and the number of grainsper cob was counted after threshing and then averaged. The mean number ofgrains per line in each cob was also determined. Grain weight was determinedby weighing 1000 grains randomly taken from the grain lot of each subplot.This was repeated thrice and the average weight was used. At maturity fourcentral rows were harvested. Cobs were dried, shelled, and weighed. Grainyield was expressed in kg ha−1. The stover of maize harvested for grain yieldwas dried and weighed to estimate stover yield.

Statistical Analysis

Data were subjected to analysis of variance (ANOVA) according to themethods described in Steel and Torrie (1980), and treatment means werecompared using the least significant difference (LSD) at P ≤ 0.05. A briefsummary of ANOVA for all parameters is presented in Table 1.

TABLE 1 Summary of analysis of variance (ANOVA) for various parameters studied inthe experiment at Takhtbhai Mardan, Pakistan

S.No Parameter Urea levels (U) Urea timings (T) U × T

1 Days to tasseling ns ∗ ns2 Days to silking ns ns ns3 Days to maturity ∗ ns ns4 Plant height ∗ ∗ ns5 Mean leaf area ns ∗ ns6 Grains per cob ∗ ∗ ns7 Grains per line ns ns ns8 1000- grains weight ∗ ∗ ns9 Grain yield ∗ ∗ ns

10 Stover yield ∗ ∗ ns

∗denotes significant at P ≤ 0.05, and ns refers to not significant.

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Maize Response to Urea Spray 75

TABLE 2 Number of days to tasseling, silking and maturity as well as plant height (cm) and mean leafarea (cm2) of maize as affected by levels and timings of urea spray during 2005–06

Days to Tasseling Days to silking Days to maturity Plant height Leaf area

Urea LevelsU0 = 0% (control) 59 65 94 151 265U1 = 2% 61 66 100 164 272U2 = 4% 63 67 101 164 295U3 = 6% 62 68 101 169 294U4 = 8% 63 67 97 159 281

LSD (P ≤ 0.05) ns ns 3.3 9.1 nsUrea timings

T1 = V9 stage 59 65 97 154 256T2 = V12 stage 64 70 100 166 299T3 = VT stage — 67 98 161 284T4 = R1 stage — 66 99 164 286

LSD (P ≤ 0.05) 1.842 ns ns 6.086 20.32

RESULTS

Phenology

Data on days to tasseling, silking, and maturity are given in Table 2. Ureaapplication timing had a significant effect on number of days to tasselingwhich was 64 days when urea was sprayed at the V12 stage as compared to59 days when sprayed at the V9 stage. Neither the level nor timing of ureahad a significant effect on silking. However, silking was delayed to 70 dayswhen urea was sprayed at the V12 stage compared to 65 days when sprayedat the V9 stage. Silking was delayed to 68 days when foliar urea was sprayedat the rate of 6%, while earlier silking (65 days) was observed in the ureacontrol plots. Urea timing and interaction had nonsignificant effects ondays to maturity, while urea levels had significant effect on days to maturity.Maturity was delayed significantly from 94 to 101 days when urea level wasincreased from zero (control) to 4 or 6% but was enhanced to 97 days whensprayed at the highest rate of 8%.

Growth

Both timing and levels of urea had significant effects on plant height(Table 2). Plants were as tall as 166 cm when urea was sprayed at the V12stage compared to 154 cm when sprayed at the V9 stage. There was nosignificant difference in maize heights when urea was sprayed at the V12,VT, and R1 stages. Also, plants were at their maximum height (169 cm) whenurea was sprayed at the rate of 6%. The maximum mean leaf area of 299 cm2

was obtained when urea was sprayed at the V12 stage and the minimum of256 cm2 was obtained when sprayed at the V9 stage (Table 2). There were

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76 Amanullah et al.

TABLE 3 Number of grains per cob and per line, 1000-grains weight (g) and grain and stover yields(kg ha−1) of maize as affected by levels and timing of urea spray during 2005–06

Grains cob−1 Grains line−1 1000-grains weight Grain yield Stover yield

Urea LevelsU0 = 0% (control) 307 24 236 1628 5789U1 = 2% 371 28 253 2147 7036U2 = 4% 384 26 262 2209 7731U3 = 6% 406 29 266 2261 8176U4 = 8% 353 26 254 2157 6697

LSD (P ≤ 0.05) 23.3 ns 15.9 418.2 1260Urea timings

T1 = V9 stage 354 26 236 1007 4947T2 = V12 stage 404 27 278 2989 8345T3 = VT stage 398 27 260 2475 8107T4 = R1 stage 300 27 244 1850 6944

LSD (P ≤ 0.05) 24.11 ns 11.67 264.4 3002

no significant differences in leaf area when urea was sprayed at V12, VT andR1 stages (284–299 cm2).

Grain Yield and Yield Components

Both timing and urea level had significant effects on the number ofgrains per cob (Table 3). The highest number of grains per cob (404) wasobserved when urea was sprayed at the V12 stage and the lowest (300) wasin cobs fertilized at the R1 stage. Urea spray at the rate of 6% yielded themost grains (406) per cob, being significantly more than the number innon-fertilized cobs (307). Urea timings and levels had no significant effectson the number of grains per line (Table 2), which ranged between 26 and27 grains per line when urea was sprayed at different stages, and between 24and 29 grains when urea was sprayed at different levels.

Both timing and urea levels had a marked effect on (1000) grain weight(Table 3). Grain weight was increased significantly when urea spray wasdelayed up to the V12 stage but further delays up to the VT and R1 stagessubstantially reduced grain weight. The highest (1000) grain weight of 278 gwas recorded when urea was sprayed at the V12 stage and the lowest weight of236 g was recorded when sprayed at the V9 stage. The grain weight increasedsignificantly with urea levels and the peak weight was obtained at the urearate of 6% (266 g/1000-grains).

Data for grain yield are given in Table 3. The highest grain yield of 2989kg ha−1 was obtained when urea was sprayed at the V12 stage, followed by2475 kg ha−1 for urea sprayed at the VT stage; the lowest yield of 1007 kg ha−1

was obtained for urea sprayed at the V9 stage. Urea spray at the rate of 6%gave the best yield of 2261 kg ha−1, followed by 2209 kg ha−1 when sprayedat the rate of 4%; the control plots yielded only 1628 kg ha−1.

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Maize Response to Urea Spray 77

Stover Yield

The highest stover yield (8345 kg ha−1) was obtained for urea sprayed atthe V12 stage, while the lowest yield (4947 kg ha−1) was for urea sprayed at theV9 stage (Table 3). There was no significant change in stover yield when ureawas sprayed either at the V12 or VT stage. The urea rate of 6% gave the high-est stover yield of 8176 kg ha−1, followed by 7731 kg ha−1 when sprayed at therate of 4%; the control plots yielded the lowest stover yield of 5789 kg ha−1.

DISCUSSION

Late application of foliar urea increased the vegetative growth period ofmaize, resulting in the late initiation of tassels. Foliar urea had no significanteffect on silking as noted earlier in Douby et al. (2000), but comparativelydelayed it when applied at the V12 stage at the rate of 6%. Maturity wassignificantly delayed when urea level was increased up to 4 and 6%, but anincrease in urea rate up to 8% and non application of urea hastened maturitysignificantly. These results are in close conformity with those of Karim et al.(1983) who reported delayed tasseling and maturity with urea spray.

Late application of urea increased plant height and leaf area especiallyat the urea rate of 6% possibly due to the extended growth period of maize.Shimshi (1967) reported that foliar applications of urea (N) to chloroticleaves of N-deficient maize restored both normal chlorophyll content andnormal stomatal behavior to the treated leaves which possibly favored plantgrowth and leaf area expansion in maize.

The number of grains per cob showed a positive relationship with urealevel up to 6% especially when applied at the V12 stage. Increases in grainnumber per cob in fertilized plots were reported by Sanjeev et al. (1997).Timing and level of foliar urea application had nonsignificant effects onnumber of grains per line. This observation contrasts with the report (Doubyet al., 2000) of significant impacts of N application on the number of seedsper line in maize. Individual grain weight or 1000 grain weight is regarded asthe basis for final economic yield. The grain weight increased with gradualincrease in foliar urea level from zero up to 6% and then decreased with thehighest level of urea up to 8%. Urea at the rate of 6% not only producedmaximum leaf area, but also maintained functional leaf area for a longer timewhich might favor increased in photo-assimilate formation that increasedseed weight. Our results are in close confirmation with those obtained bySanjeev et al. (1997) who reported heavier maize seed with foliar N.

The increase in grain yield with urea application at the V12 stage mightbe due to the extended growth period, increase in grain weight and numberof grains per cob. On the other hand the lowest grain yield in the plotsapplied with urea at the V9 stage might be due to the reduced growth period,decrease in grain weight and number of grains per cob. Gooding and Davies

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78 Amanullah et al.

(1992) reported that foliar urea (N) applications increased grain yield inmaize, particularly when applied before flag leaf emergence and when Navailability was limiting. However, Below et al. (1985) noted that grain yieldwas unaffected by the spray treatment after anthesis to enhance or extend theaccumulation of dry weight. The highest grain yield was obtained when ureawas applied at the rate of 6%. The increase in grain yield at this urea was dueto the extension in the growth period of maize, increase in grain weight andnumber of grains per cob. Singh et al. (2005) suggested that a supplementaldose of 7 kg N ha−1 as urea spray significantly increased maize grain yield.However, Ma et al. (2004) found that foliar N spray had no significant effectson grain yield of maize as compared to soil application of N. The highestlevel of urea (8%) spray caused severe leaf burn (plasmolysis) that adverselyaffected normal physiological processes, reduced leaf area, yield, and yieldcomponents of maize.

Stover yield increased significantly when foliar urea was applied at theV12 stage possibly due to the extended growth period of maize, and increasein plant height and average leaf area. Woolfolk et al. (2002) reported thatlate season foliar N application increased stover yield and total straw N.However, Below et al. (1985) noted that stover yield was unaffected by thefoliar treatment after anthesis. The highest stover yield was obtained whenfoliar urea was applied at the rate of 6% for the same reason that it increasedyield above. Ma et al. (2004) reported that foliar N spray had no significanteffects on the stover yield of maize.

CONCLUSION

Improper N applications particularly with continued soil nutrient miningare major factors contributing to low crop yield in north-western Pakistan.Our findings suggest that foliar urea application at the V12 stage and atthe rate of 6% would significantly increase both grain and stover yieldsof maize. Farmers in the NWFP who traditionally apply all urea at sowingrequire demonstration of the benefits of foliar urea application. Furtherresearch work for understanding the impacts of levels and timing of foliarurea application for highly sustainable maize production in different agro-ecological conditions of NWFP is suggested.

ACKNOWLEDGMENTS

Director of the Jamra Seed Production and Demonstration Farm,Takhtbhai Mardan is acknowledged for his sincere cooperation and tech-nical support during the experiment.

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