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This article was downloaded by: [University of Delaware] On: 05 October 2014, At: 10:31 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Plant Nutrition Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lpla20 Plant Responses of Ultra Narrow Row Cotton to Nitrogen Fertilization J. S. McConnell a , P. B. Francis b , C. R. Stark b & R. E. Glover c a Western Illinois University, Institute for Environmental Studies , Macomb, Illinois, USA b University of Arkansas at Monticello , Monticello, Arkansas, USA c Northeast Research and Extension Center , Keiser, Arkansas, USA Published online: 05 Jun 2008. To cite this article: J. S. McConnell , P. B. Francis , C. R. Stark & R. E. Glover (2008) Plant Responses of Ultra Narrow Row Cotton to Nitrogen Fertilization, Journal of Plant Nutrition, 31:6, 1005-1017, DOI: 10.1080/01904160802097201 To link to this article: http://dx.doi.org/10.1080/01904160802097201 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages,

Plant Responses of Ultra Narrow Row Cotton to Nitrogen Fertilization

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This article was downloaded by: [University of Delaware]On: 05 October 2014, At: 10:31Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK

Journal of Plant NutritionPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/lpla20

Plant Responses of UltraNarrow Row Cotton to NitrogenFertilizationJ. S. McConnell a , P. B. Francis b , C. R. Stark b & R.E. Glover ca Western Illinois University, Institute forEnvironmental Studies , Macomb, Illinois, USAb University of Arkansas at Monticello , Monticello,Arkansas, USAc Northeast Research and Extension Center , Keiser,Arkansas, USAPublished online: 05 Jun 2008.

To cite this article: J. S. McConnell , P. B. Francis , C. R. Stark & R. E. Glover (2008)Plant Responses of Ultra Narrow Row Cotton to Nitrogen Fertilization, Journal of PlantNutrition, 31:6, 1005-1017, DOI: 10.1080/01904160802097201

To link to this article: http://dx.doi.org/10.1080/01904160802097201

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all theinformation (the “Content”) contained in the publications on our platform.However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness,or suitability for any purpose of the Content. Any opinions and viewsexpressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of theContent should not be relied upon and should be independently verified withprimary sources of information. Taylor and Francis shall not be liable for anylosses, actions, claims, proceedings, demands, costs, expenses, damages,

and other liabilities whatsoever or howsoever caused arising directly orindirectly in connection with, in relation to or arising out of the use of theContent.

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Journal of Plant Nutrition, 31: 1005–1017, 2008

Copyright © Taylor & Francis Group, LLC

ISSN: 0190-4167 print / 1532-4087 online

DOI: 10.1080/01904160802097201

Plant Responses of Ultra Narrow Row Cottonto Nitrogen Fertilization

J. S. McConnell,1 P. B. Francis,2 C. R. Stark,2 and R. E. Glover3

1Western Illinois University, Institute for Environmental Studies, Macomb,Illinois, USA

2University of Arkansas at Monticello, Monticello, Arkansas, USA3Northeast Research and Extension Center, Keiser, Arkansas, USA

ABSTRACT

Recent developments in cotton (Gossypium hirsutum L.) production technology in theMississippi River Delta region include drill planting cotton. Production systems thatinclude drill planting cotton are referred to as ultra narrow row (UNR). Ultra narrowrow cotton production is a low input system designed to maximize economic returns.Cotton grown under UNR systems is generally lower yielding and lower returning thanconventionally spaced cotton, but the inputs and input costs are also generally reducedcompared to conventionally spaced cotton production systems. Studies were conductedfor five location-years in southeastern and northeastern Arkansas to determine the opti-mum N-fertilizer rate for UNR cotton. Plant maturity was estimated using nodes abovewhite flower (NAWF) measurements. The NAWF indicated that greater nitrogen (N)-rates delayed maturity of the crop, although differences were not always significant.Lint yields were significantly different in only three of five location-years. Yield re-sponses of UNR cotton tended to maximize with N-treatments between 56 and 84 kgN ha−1 when significant differences were observed. Plant height, similar to lint yield,was significantly different due to N-treatments in three out of five location-years, andgenerally increased with increasing N-fertilization up to 112 kg N ha−1. Boll load wassignificantly influenced by N-fertilization in only two of five location years. In these twoinstances, 84 kg N ha−1 was sufficient to maximize boll load. Boll weight, a componentof yield, was determined in the southern Arkansas location only. Significant differencesin boll weight due to N-fertilization were found in only two of four years. Boll weightgenerally increased with increasing N-fertilization.

Received 22 June 2006; accepted 16 March 2007.Address correspondence to J. S. McConnell, The Institute for Environmental Sci-

ences, 1 University Circle, Tillman Hall 301, Macomb, IL 61455-1390. E-mail:[email protected]

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1006 J. S. McConnell et al.

Keywords: Gossypium hirsutum, nitrogen, ultra narrow row cotton

INTRODUCTION

Some grain crops planted in narrow rows have long been known to utilizesunlight more efficiently than those planted in widely spaced rows (Andradeet al., 2002; Shibles and Weber, 1966). Yet traditionally, row spacing optionsfor cotton production were limited in the Mississippi River Delta region. Rowspacing in cotton is generally wider than most crops to accommodate harvestequipment and to facilitate control of weed and insect pests (Wright et al.,2000). Cotton is typically grown in rows ranging from 0.76 m to 1.02 m wide.Research of the narrowest of conventional row spacings, 0.76 m, indicates thatimprovement of plant architecture increases sunlight interception, boll load,and lint yield of cotton (Reta-Sanchez and Fowler, 2002).

Efficient nitrogen (N) nutrition of cotton (Gossypium hirsutum L.) is criti-cal for economically successful production. If cotton becomes N deficient theplants may become chlorotic and not photosynthesize sufficiently to meet thedemands of crop growth (Radin and Mauney, 1984). Nitrogen deficiency ofcotton typically results in reduced yields, pre-mature cut out, and reduced fiberquality (Waddle, 1984). Reductions in yield and quality may severely reducethe value of the crop (Bondada et al., 1996). Reduction of crop value without alarge decrease in production costs is not conducive to economically successfulcrop production.

Recent developments in cotton production technology in the MississippiRiver Delta region include drill planting cotton in ultra narrow row (UNR)production systems. Ultra narrow row cotton is a low input production systemdesigned to maximize economic returns. The rows of UNR cotton are roughlyspaced between 10 and 25 cm. The premise is that UNR cotton will be loweryielding, but the reduction in input costs will result in a larger profit margin.Research that provides information on production parameters including N-fertilization for UNR cotton is scant. Studies of the interactions of N-rateswith plant populations of UNR cotton on loess soils indicates little effect ofN-fertilization rate on either lint yield or yield components (Boquet, 2005).

The objective of this research was to determine the N-fertilization ratenecessary to optimize yield, growth and maturity of UNR cotton grown on thealluvial flood plains of the Mississippi River Delta region.

MATERIALS AND METHODS

Experiments to examine the responses of UNR cotton to N-fertilization werebegun in 1998 and concluded after the 2001 growing season at the South-east Branch Experiment Station (SEBES) near Rohwer, Arkansas. The soil at

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UNR Cotton and Nitrogen Fertilization 1007

the SEBES site was an Hebert silt loam (fine-silty, mixed, thermic Aeric Or-chraqualfs). The test was expanded for the 1999 growing season to include asecond study site at the Northeast Research and Extension Center (NEREC)near Keiser, Arkansas. The soil at NEREC was a Sharkey silty clay (very fine,smectitic, thermic Chromic Epiaquerts). Stoneville 474 was the cultivar used allfour years and both locations of the study. Stand failure precluded continuingthe test at NEREC in 2000. Low system input with respect to tillage and irriga-tion for UNR cotton was designed to simulate conditions that cotton growersmight impose to reduce cost of production.

The experimental design at both locations was randomized complete blockwith eight replications. Individual plot size was 3.048 m by 6.096 m for anarea of 18.58 m2. The test borders were delineated for year-to-year continuity.Plot integrity was maintained at the SEBES location with the same treatmentsapplied to the same plots in the same locations all four years of the study.

The fertilizer N source was urea (46% N) for these studies all years at alllocations. Nitrogen treatments rates were 0-, 28-, 56-, 84-, 112-, and 140-kg Nha−1. All N-treatments were applied to the soil surface without incorporationwhen the crop reached the two true leaf stage. There were no split applicationsemployed in these studies. Typically, rainfall is frequent in the Delta region dur-ing the late spring, and rapid dissolution of the urea by rainfall and subsequentinfiltration carried the N into the soil is likely.

The site was disked and smoothed prior to planting each year. Cotton wasdrill planted at the test site in narrow, 18 cm rows. Planting dates for SEBESwere: 3 June 1998, 17 May 1999, 16 May 2000, 23 May 2001. The plantingdate for NEREC was 21 May 1999. The cotton was not tilled after planting. Noirrigation was used at any time during the trials. Diseases, insects and weedswere controlled using recommended agronomic practices for conventionallyrow-spaced cotton (Bonner, 1995).

Plant development and maturity was determined periodically through thegrowing season using nodes above white flower (NAWF) measurements (Bour-land et al., 1992). The first NAWF measurements were taken near time of firstflower and roughly 50 d after planting (DAP) each year of the study. The NAWFvalues for five randomly selected plants from each plot were averaged. Meansof treatments from four replications were used to determine the treatment mean.Measurements were continued during the growing season until mean NAWFvalues became approximately two or less.

Final measurements were taken from randomly selected one meter squareareas, designated the harvest area, within each plot. The number of plants withinthe harvest area were determined to calculate the surviving plant populationthat contributed to yield. The heights of five randomly selected plants from theharvest area were averaged for the mean plant height. The number of bolls onthe plants within the harvest area were then counted to determine boll load ofthe crop. The number of bolls was divided by the number of plants to calculatethe bolls per plant. All plants within the square meter were hand harvested

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to determine seed cotton yield. The harvested seed cotton and the number ofbolls per square meter were then used to ascertain the boll weight. The lintwas then separated from the seed in each square meter from each plot usinga small laboratory gin and the lint fraction was determined. Lint fraction wasthen multiplied by the seed cotton yield to calculate the lint yield.

Following the final year of study, the plots from four replications within theSEREC study were sampled to a depth of 60 cm in 15 cm segments in the earlyspring of 2002. The samples were air dried, ground and analyzed for NO−

3 -N in a 2:1 water-soil slurry using a modified ion specific electrode technique(Mulvaney, 1996) at the University of Arkansas - Soil Testing Laboratory.

All data were analyzed using the Statistical Analysis System (SAS). F-testsand least significant differences (LSD) were calculated at the α = 0.05 level ofprobability.

RESULTS AND DISCUSSION

Plant Development

Node Development was evaluated using nodes above white flower (NAWF)measurements and techniques described previously (Bourland et al., 1992).Previous research that included NAWF measurements in N-fertilization studiesof conventionally row-spaced cotton have shown large NAWF values, generallynear 9.0, as means near the time of first flower with higher means for greaterN-rates (Bourland et al., 1997; McConnell et al., 1992). All means for all N-treatments declined erratically as the growing season progressed ( McConnell etal., 1992; McConnell and Mozaffari, 2004). Initial observations indicated thatnodal development of UNR cotton differed substantially from cotton grown inconventionally spaced rows.

First year results contained some of the highest NAWF means observedin any year of the experiment (Table 1). Although NAWF means were notsignificantly different for the first two sampling dates, there was a very generaltrend of increasing NAWF with increasing N. The first NAWF evaluations (56DAP) were taken just after the plants began flower, but N-treatments did notproduce significant differences. The mean NAWF of all treatments at 56 DAPduring the first year of study was 5.9, the greatest mean value for any measuringdate. A NAWF value of five or less is indicative of physiologically matureplants that are near ‘cut out’ in conventionally row spaced cotton (Bourlandet al., 1997). As with conventionally row spaced cotton, the NAWF meansfor all treatments declined irregularly through the growing season. Significantdifferences in NAWF means due to N-treatments were observed 71 DAP and77 DAP in 1998. The greatest N-treatment, 140 kg N ha−1, produced the largestmean NAWF values; while the unfertilized control produced the lowest NAWFvalues. Two groups of NAWF means were observed on both 71 and 77 DAP.

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UNR Cotton and Nitrogen Fertilization 1009

Table 1Nodes above white flower (NAWF) measurement with time of cotton grown in ultranarrow row treated with 0, 28, 56, 84, 112, 140 kg urea-N/ha at the Southeast BranchExperiment Station near Rohwer, AR during 1998

Date and days after planting (DAP)

56 DAP 63 DAP 71 DAP 77 DAPN-Rate 29 July 5 Aug 13 Aug 19 Aug- kg N ha −1 - - NAWF -

140 5.5 3.7 3.8 3.1112 6.1 4.4 2.8 2.584 6.0 4.7 2.8 2.656 6.5 4.7 2.3 1.628 5.9 4.0 2.2 1.20 5.3 3.3 1.3 0.7LSD (0.05) NS NS 0.7 0.7

The 84-, 112-, and 140-kg N ha−1 treatments had greater NAWF means thanthe three lowest N-treatments.

Node development during the second year of the trial, 1999, was substan-tially different from the first year (Table 2). Values of NAWF just after theinitiation of flowering (52 DAP) were low, with an overall mean of only 3.4,and did not differ significantly as a function of N-rate. Means of NAWF weregreater 59 DAP than at 52 DAP, and exhibited significant differences due to

Table 2Nodes above white flower (NAWF) measurement of cotton grown in ultra narrow rowwith 0, 28, 56, 84, 112, 140 kg urea-N/ha at the Southeast Branch Experiment Stationnear Rohwer, AR during 1999

Date and days after planting (DAP)

52 DAP 59 DAP 66 DAP 72 DAP 78 DAPN-Rate 8 July 15 July 22 July 28 July 3 August- kg N ha −1 - - NAWF -

140 4.0 6.0 5.2 .0 1.6112 3.6 5.5 4.1 3.0 1.984 3.8 5.2 3.8 2.7 1.656 3.0 5.2 4.5 2.1 1.028 3.1 4.3 3.7 1.7 0.60 3.0 4.3 2.7 0.9 0.4LSD (0.05) NS 1.7 NS 0.7 0.6

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N-treatments. Lowest mean NAWF were observed with 0- and 28 kg N ha−1

with gradual increases within increasing N-fertilization. A general decline in theNAWF means was observed from 59 DAP to 66 DAP with no significant differ-ences that could be attributed to N-treatment. Similar to 1998, the two final setsof measurements of NAWF seemed divided readily into two groups; the higherN-treatments with greater NAWF means, and the three lower N-treatments withsmaller NAWF means.

Third year results exhibited the expected trend of declining NAWF meanswith time (Table 3), similar to the first year results. Significant differencesdue to N-treatments were found near first flower (51 DAP), at 57 DAP, and inearly August (77 DAP). Initial NAWF means (51 DAP and 57 DAP) generallywere greater with greater N fertilization. Reversals in this trend were observedbetween the140- and 112-kg N ha−1 treatments at 51 DAP, as well as the140-and 112-kg N ha−1 treatments and the 56- and 28-kg N ha−1 treatments at 57DAP, although the differences were not significant.

Mean NAWF values during the fourth year of the study were generallythe lowest observed of any year (Table 4). Compression of the range of meansprecluded much meaningful information from these measurements. Significantdifferences due to N-treatments were found near first flower (57 DAP), andin late July (72 DAP), although few differences were significant within thesetwo sampling periods. Mean NAWF during the 57 DAP period appear to begrouped into the three greatest N-treatments and the three least N-treatments.No discernable pattern was observed in the NAWF means at 72 DAP, althoughsignificant differences were indicated.

Table 3Nodes above white flower (NAWF) measurement of cotton grown in ultra narrow rowwith 0, 28, 56, 84, 112, 140 kg urea-N/ha at the Southeast Branch Experiment Stationnear Rohwer, AR during 2000

Date and days after planting (DAP)

51 DAP 57 DAP 64 DAP 71 DAP 77 DAPN-Rate 6 July 12 July 19 July 26 July 1 August- kg N ha −1 - - NAWF -

140 6.3 5.6 4.4 2.3 1.8112 7.2 6.0 4.4 2.6 1.684 5.2 5.8 4.4 2.7 1.556 5.0 4.6 4.1 2.1 1.228 5.0 5.2 3.7 1.8 0.60 4.8 4.5 3.4 1.7 1.0LSD (0.05) 1.2 0.9 NS NS 0.7

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UNR Cotton and Nitrogen Fertilization 1011

Table 4Nodes above white flower (NAWF) measurement of cotton grown in ultra narrow rowwith 0, 28, 56, 84, 112, 140 kg urea-N/ha at the Southeast Branch Experiment Stationnear Rohwer, AR during 2001.

Date and days after planting (DAP)

46 DAP 57 DAP 65 DAP 72 DAP 78 DAPN-Rate 5 July 16 July 24 July 31 July 6 August- kg N ha −1 - - NAWF -

140 2.3 4.4 4.5 2.3 2.1112 2.2 4.5 3.8 2.8 1.184 2.3 4.4 3.6 1.9 1.656 1.8 3.2 3.1 1.5 1.328 1.8 3.5 3.9 1.6 1.00 1.5 3.3 3.5 2.0 2.0LSD (0.05) NS 0.9 NS 0.9 NS

Plant Height

Final mean plant height of the cotton plants was significantly influenced byN-treatment in three of four years at SEBES and in 1999 at NEREC (Table 5).Plants tended to irregularly increase in height with increasing N-rate, although

Table 5Plant height of cotton grown in ultra narrow row with 0, 28, 56, 84, 112, 140 kg urea-N/ha at the Southeast Branch Experiment Station near Rohwer, AR from 1998 to 2001,and at the Northeast Research and Extension Center during 1999

Year

N-Rate 1998 19991 19992 2000 2001- kg N ha −1 - - cm -

140 69.9 26.9 52.5 64.8 57.1112 77.5 29.0 54.1 60.2 55.484 66.8 32.5 53.1 57.9 45.656 62.0 30.7 52.0 48.0 46.728 51.8 29.0 45.1 47.8 36.90 50.5 31.0 41.8 44.7 40.3LSD (0.05) 10.7 NS 6.6 7.4 8.1

1Southeast Branch Experiment Station.2Northeast Research and Extension Center.

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not all differences were significant and some non-significant reversals wereobserved. Tallest cotton plants were always associated with the two greatestN-treatments, 112- and 140 kg N ha−1, all years when significant differenceswere observed. Shortest plants were found in the unfertilized control all yearsof the study except 2001. During 2001, the mean plant height of the plantstreated with 28 kg N ha−1 was least, but not significantly less than the heightproduced by the 0 kg N ha−1 rate.

Boll Load

Boll load of the cotton was significantly influenced by the N-treatments all yearsexcept 1999 (Table 6). No significant boll load response to N-treatment wasobserved during 1999 at either SEBES or NEREC. Similar to final plant height,boll load tended to irregularly increase with increasing N-rate, although not alldifferences were significant and some non-significant reversals were observed.Greatest boll loads were always associated with the highest N-treatment, 140kg N ha−1, except in 1999 when no significant differences were observed. Nosignificant increases in boll load were observed with treatments greater than 56kg N ha−1 in either 1998 or 2001. The greatest boll loads in 1999 were producedby the112- and 140-kg N ha−1 treatments. Lowest boll loads were producedby the untreated control treatment each year of the study, although differenceswere not always significant.

Table 6Boll load of cotton grown in ultra narrow row with 0, 28, 56, 84, 112, 140 kg urea-N/haat the Southeast Branch Experiment Station near Rohwer, AR from 1998 to 2001, andat the Northeast Research and Extension Center during 1999

Year

N-Rate 1998 19991 19992 2000 2001- kg N ha −1 - - boll ha −1 -

140 864,133 653,332 627,466 669,777 592,889112 810,310 625,353 713,589 574,095 499,34284 844,697 553,165 590,556 539,708 556,15556 793,866 570,677 744,347 450,006 436,55228 689,213 553,165 713,589 452,784 399,8150 473,928 472,433 553,646 364,789 345,139LSD (0.05) 118,771 NS NS 99,146 162,332

1Southeast Branch Experiment Station.2Northeast Research and Extension Center.

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Table 7Boll weight of cotton grown in ultra narrow row with 0, 28, 56, 84, 112, 140 kg urea-N/haat the Southeast Branch Experiment Station near Rohwer, AR from 1998 to 2001

Year

N-Rate 1998 1999 2000 2001- kg N ha −1 - - g boll −1 -

140 3.31 2.70 2.67 2.933.39 2.55 2.46 2.7284 3.30 2.76 2.41 2.4756 3.12 2.45 2.34 2.8428 2.93 2.41 1.98 2.370 2.84 2.49 2.22 2.34LSD (0.05) 0.28 NS 0.40 NS

Boll Weight

Boll weight of the cotton was significantly influenced by the N-treatments two offour years at SEBES (Table 7). General increases in boll weight were observedwith increasing N-fertilization to 56 kg N ha−1. Boll weights of cotton treatedwith N-rates exceeding 56 kg N ha−1 were not significantly different. Althoughseed weight was not determined, it is presumable that seed weight was a factorin the differences in boll weight when significant differences were observed.Well nourished seed tend to be larger and heavier, thereby adding to the weightof a boll compared to under fertilized or water stressed cotton (Cherry andLeffler, 1984).

Lint Yield

Significant differences among years and locations, as well as significant inter-actions among years and treatments precluded pooling mean yields over years.Lint yields were significantly influenced by the N-treatments all years except atSEBES in 1999 (Table 8). The N-fertilization rate necessary to produce maxi-mum yield varied extensively among years. Four out of five location-years an Napplication of 84 kg N ha−1 was adequate to meet the demands of the developingcotton crop and optimize yield and earliness of UNR cotton. Trends of highervalues were observed with greater N-rates some years, but the differences werenot usually significantly different from 84 kg N ha−1 treatment.

Year-by-year differences in yield trends indicates substantial impact ofclimate on yield response of UNR cotton to N-fertilization (Table 8). The N-fertilization rate necessary to produce maximum yield was 140 kg N/ha in 1998.

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Table 8Lint yield of cotton grown in ultra narrow row with 0, 28, 56, 84, 112, 140 kg urea-N/haat the Southeast Branch Experiment Station near Rohwer, AR from 1998 to 2001, andat the Northeast Research and Extension Center during 1999

Year

N-Rate 1998 19991 19992 2000 2001- kg N ha −1 - - kg lint ha −1 -

140 1187 784 390 726 729112 1157 715 403 590 63384 1158 670 393 540 63156 1007 614 373 430 58828 834 613 346 375 4750 524 531 242 347 392LSD (0.05) 171 NS 93 123 242

1Southeast Branch Experiment Station.2Northeast Research and Extension Center. Lint yield was determined by multiplying

seed cotton yield by 0.35.

Drought conditions masked the impact of N-fertilization of the UNR cotton in1999 at both locations. The lack of significant yield differences at SEBESand limited differences at NEREC when the crop was drought stressed wasan expected result. Nitrogen fertilization of conventionally row-spaced cottonhas been shown to be ineffective under severe water deficit (McConnell andMozaffari, 2004; McConnell et al., 1998). Lint yields from the 2000 and 2001growing seasons at SEBES increased with increasing N-rates up to 140 kgN ha−1, although not all differences were significant. Prolonged periods ofrainfall and saturated soil conditions characterized both the 2000 and 2001growing seasons. Denitrification of the surface applied, unincorporated urea-Nand ammonia (NH3) volatilization may have deprived the developing crop ofN, thereby reducing lint yield. As the N-rate was increased, more N would beavailable to the crop coinciding with increasing yields.

Soil Nitrate-N Analysis

Analysis of the nitrate (NO−3 )-N content of the soil from the plots indicated

no significant differences among N-treatments or soil depths after completionof the test in the early spring of 2002 to a depth of 60 cm (Table 9). Thiscontrasts with conventional row-spaced cotton plants where distinct zones ofaccumulation are evident (McConnell et al., 1996). The range of soil NO−

3 -Nvalues was compressed between 1 kg NO−

3 -N kg−1 of soil and 3 kg NO−3 -N

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UNR Cotton and Nitrogen Fertilization 1015

Table 9Soil nitrate-nitrogen (NO−

3 -N) distribution in ultra narrow row cotton treated with 0,28, 56, 84, 112, 140 kg urea-N ha−1 at the Southeast Branch Experiment Station nearRohwer, AR during 2002. No significant differences were detected

N-Rate (kg urea-N ha −1)

Depth 0 28 56 84 112 140- cm - - kg NO−

3 -N kg −1 -

0–15 2 3 3 3 3 215–30 2 1 2 2 2 130–45 2 2 2 2 2 145–60 2 2 3 3 2 2

kg−1 of soil with no discernable pattern or trend. The low concentrations of soilNO−

3 -N found throughout these studies indicates that mechanisms of removalof soil NO−

3 -N were sufficient to prevent any substantial accumulation of NO−3

even at the high N-rate, 140 kg N ha−1. The mechanisms most likely to haveimpacted the soil N status in these studies were ammonia (NH3) volatilizationas urea decomposed on the soil surface, denitrification as the surface applied Nwas subjected to wetting and drying cycles, and crop uptake.

CONCLUSIONS

Current University of Arkansas N-fertilizer recommendations for cotton beginwith a base value of 112 kg N ha−1 . Additions and subtractions to this basevalue are recommended with differences in soil texture, soil calcium content,and crop history of the field (Chapman and Daniels, 2000). The N-fertilizerrecommendation for the SEBES study site would be 112 kg N ha−1 to optimizecotton yield. The responses of UNR cotton to N fertilization treatments indicatethat the N required for maximum yield will be less than the 112 kg N ha−1 rec-ommended for cotton grown in conventionally spaced rows and depended onyear-to-year climate. Yields of UNR cotton were found to erratically increasewith N rates above 84 kg N ha−1. Additionally, the 56 kg N/ha treatment wasusually found to maximize both the boll load and boll weight. The parametersmeasured in these studies suggest that the N-fertilization to optimize UNR cot-ton is substantially different from the recommended N-rates for conventionallygrown cotton.

ACKNOWLEDGMENTS

This work was supported with funding by the Arkansas Fertilizer Tonnage Fee.

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