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SOIL FERTILITY

Nitrogen Fertilization of No-Till Cotton on Loess-Derived Soils

^a Plant and Soil Sciences Dep., Univ. of Tennessee, West Tennessee Exp. Stn., Jackson, TN 38301
^b Plant and Soil Sciences Dep., Univ. of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071
^c Agric. Economics and Rural Sociology Dep., Univ. of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071

Corresponding author (dhoward2{at}utk.edu)

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Information on nitrogen (N) fertilization of no-till (NT) cotton (Gossypium hirsutum L.) is needed to optimize lint yields and earliness. We evaluated five N rates and three application methods for NT cotton production on Loring silt loam (fine-silty, mixed, active, thermic Oxyaquic Fragiudalfs) with natural winter annuals as a cover; and on Memphis silt loam (fine-silty, mixed, active, thermic Typic Hapludalfs) having corn (Zea mays L.) stover as a cover and on Lexington silt loam (fine-silty, mixed, active, thermic Utlic Hapludalfs) having winter wheat (Triticum aestivum L.) as a cover. Nitrogen rates of 0, 34, 67, 101, and 134 kg ha^-1 were either broadcasted as ammonium nitrate (AN) or injected as urea–ammonium nitrate (UAN) at planting. Additional treatments included broadcasting 67 kg N ha^-1 as AN at planting with either 34 or 67 kg N ha^-1 banded 6 wk later. Relative to no N, broadcasting 67 kg N ha^-1 as AN increased 4-yr average NT lint yields on Loring silt loam from 739 to 1281 kg lint ha^-1 and 2-yr average yields on Lexington silt loam from 1086 to 1535 kg ha^-1. A higher N rate (101 kg N ha^-1) was needed to increase 2-yr average yields on Memphis silt loam from 821 to 1169 kg ha^-1. Broadcasting AN was a satisfactory placement method producing yields equal to or higher than injecting UAN or splitting AN for NT cotton produced on these loessial soils despite different covers and residues.

Abbreviations: AN, ammonium nitrate • UAN, urea–ammonium nitrate • DD60, degree days 60 • NT, no-tillage • CT, conventional-tillage

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
NITROGEN (N) fertilization affects yield, maturity, and lint quality of cotton. Evaluating N rates, sources, and application timing for optimum lint production has been a major research emphasis within the cotton producing states. For cotton, applying an optimum N rate is essential and may differ within the production areas due to climatic or soil differences. An optimum N rate should maximize yields, while excessive or inadequate N applications may reduce cotton yields (Maples and Keogh, 1971). High N fertilization may produce excessive vegetation that delays maturity and harvest, and these conditions may reduce yields and lint quality during years of early frost or prolonged fall rain (Hutchinson et al., 1995; McConnell et al., 1995). Crop maturity is a critical production consideration for cotton producers along the northern edge of the U.S. Cotton Belt (Gwathmey and Howard, 1998). Nitrogen deficiency causes premature senescence and reduced yields (McConnell et al., 1995).

Research conducted within the mid-South shows that the optimum N rate for cotton production varies with location, soil type, tillage system, winter cover, and application method. On conventionally tilled (CT) Dundee very fine sandy loam (fine-silty, mixed, active, thermic Typic Endoaqualfs), Ebelhar and Welch (1996) reported optimum yields from banding 50% of the N at planting followed by banding 50% at pinhead square. Their evaluation included N rates (67–168 kg ha^-1) and application timing (at planting and three splits) from which they concluded that the 50–50 split application of 101 kg N ha^-1 resulted in the highest yields. In an additional study, Ebelhar et al. (1996) showed that injecting a 50–50 split (at planting and pinhead) at a higher rate (134 kg N ha^-1) resulted in maximum cotton yields on CT Bosket very fine sandy loam (fine-silty, mixed, active, thermic Typic Hapludalfs) and Dubbs silt loam (fine-silty, mixed, active, thermic Typic Hapludalfs). In Mississippi, Thompson and Varco (1996) reported that broadcasting 121 kg N ha^-1 as ammonium nitrate (AN) and injecting 110 kg N ha^-1 as urea–ammonium nitrate (UAN) produced maximum NT cotton yields on Marietta fine sandy loam (fine-loamy, siliceous, active, thermic Fluvaquentic Eutrudepts). Hutchinson et al. (1995) reported the need for a higher N rate for both CT and NT cotton production on Gigger silt loam (fine-silty, mixed, active, thermic Typic Fragiudalfs) having a winter wheat cover. Their research indicated that NT yields were increased with injected N up to 78 kg ha^-1 when native winter vegetation was the cover, while yields were increased with N rates up to 118 kg ha^-1 with winter wheat.

In Tennessee, cotton yields were maximized at lower N rates than were reported for surrounding states. Yield response to N fertilization by CT cotton on well-drained loessial upland soils ranged from 34 kg N ha^-1 (Overton and Long, 1969) to 67 kg N ha^-1 (Howard and Hoskinson, 1986). From a review of Tennessee research, Howard and Hoskinson (1990) reported that CT cotton yield responses to N fertilization varied with soil and physiographic position. The current N recommendation for Tennessee cotton production, regardless of tillage, is to apply 34 to 67 kg N ha^-1 to alluvial soils and 67 to 90 kg N ha^-1 for upland soils (Univ. of Tennessee, 2000). These ranges allow the producer to select an N rate based on knowledge of cropping history and previous fertilization.

Most of the previous research in the mid-South was conducted using CT production with soil N incorporation immediately after application. Current information on N fertilization rates and application methods for NT cotton production on highly erodible loess-derived soils is limited. Conservation tillage systems such as NT with winter cover crop are recommended for erosion control on a large portion of western Tennessee cotton land area (Shelby and Bradley, 1996). When cropped, these loess-derived soils historically have had high soil erosion rates (Langdale et al., 1985) reducing productivity, especially if root-restrictive fragipans were present (Flowers et al., 1964). Fertilizers are generally surface-applied when CT systems are used. Surface broadcasting urea-containing fertilizers may result in N losses from immobilization and volatilization (Reeves et al., 1993). Howard and Essington (1998) reported that N immobilization by microorganisms in organic residues reduced NT corn yields as much as 9%. They also reported that the combination of immobilization and volatilization N losses reduced NT corn yields as much as 36% from surface-applied urea.

Surface-applied N losses by either immobilization or volatilization from urea may reduce yields (Howard and Essington, 1998). Injecting N below the soil surface restricts both N volatilization and immobilization since these two loss mechanisms are primarily associated with surface applications. However, N injection is a more expensive application method (Roberts et al., 1995) than surface broadcasting and should be used when either volatilization or immobilization losses are sufficient to reduce N yields.

The objective of this research was to evaluate the effect of broadcast, injected, and split-applied N rates on yields and earliness of NT cotton produced on loess-derived soils.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
A 4-yr study was conducted from 1994 through 1997 on a Loring silt loam at the Milan Experiment Station, Milan, TN. Two-year studies were conducted from 1996 through 1997 on a Memphis silt loam at Ames Plantation, Grand Junction, TN, and on a Lexington silt loam at the West Tennessee Experiment Station, Jackson, TN. A composite soil sample was collected to a 15-cm depth from each of the replicated blocks in 1997 to evaluate Mehlich-I extractable P and K and organic C. For the Loring, Memphis, and Lexington silt loams, Mehlich-I extractable P and K levels were 69 and 227 kg ha^-1, 75 and 138 kg ha^-1, and 222 and 356 kg ha^-1, respectively. Total C determined with a CR-12 C Analyzer (Leco Corp., St. Joseph, MO) for the three soils was 11.2, 11.2, and 11.6 g kg^-1, respectively.

Surface residues on the three soils were derived from volunteer native winter annuals on the Loring soil, winter wheat on the Lexington soil, and corn stover on the Memphis soil.

The previous crop on the Loring and Lexington soils was NT cotton, while corn was the previous crop produced on the Memphis soil. Winter wheat was fall-seeded each year following cotton harvest on the Lexington soil. Corn stover from the 1995 crop was used for both the 1996 and 1997 crops. The experimental design was a randomized complete block with five replications. Nitrogen rates of 0, 34, 67, 101, and 134 kg N ha^-1 were either broadcast as AN (34% N) or injected as urea–ammonium nitrate (UAN, 32% N) immediately after planting. These two N sources were selected because of the ease and accuracy of injecting liquids relative to dry fertilizers and the potential problems associated with broadcasting UAN for NT production (Howard and Essington, 1998). The N rate range was selected to encompass current N rates recommended for cotton production in Tennessee (Univ. of Tennessee, 2000). Treatments were applied to the same plots each year.

Broadcast AN treatments were hand-applied, while the injected treatments were applied using a four-row applicator. Urea–ammonium nitrate was injected 5 cm deep and 10 cm to the side of the row and metered through a straight stream metering orifice attached to a knife configured behind a rolling coulter. The N rates were applied using a CO₂ pressurized system. Injected N rates were established by varying application speed and/or orifice size. Additional treatments included broadcasting AN at 67 kg N ha^-1 at planting followed by side-dressing either 34 or 67 kg N ha^-1 6 wk after planting (split application). Before planting, P was broadcast at 15 kg ha^-1 using triple superphosphate while K was broadcast at 56 kg ha^-1 using potassium chloride.

The cultivar D&PL 50 was planted from 1994 through 1996, and D&PL 5409 was used in 1997. Experiments were planted between early- and mid-May at all locations at approximately 190000 seed ha^-1. Individual plots were four rows wide with a 0.97-m row spacing on Lexington soil and a 1.02-m row spacing on Loring and Memphis soils. Plot lengths were 9.1 m at each location. Before planting, winter vegetation (wheat or native) was killed with paraquat (1,1'-dimethyl-4.4'-bipyridinium ion) applied at 712 g a.i. ha^-1 containing 0.5% (v/v) nonionic surfactant. Residual weed control included broadcasting pendimethalin {N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine} at 930 g a.i. ha^-1 plus fluometuron {N,N-dimethyl-N'-[trigluoromethyl-phenyl]urea} at 1121 g a.i. ha^-1. Additional recommended production practices (insecticides, defoliants, etc.) were used at each location (Shelby, 1996).

A recommended defoliant was applied when 60% of the bolls were open. Lint yields were determined by mechanically picking the two center rows of each plot twice. Cotton was picked approximately 2 wk after leaf drop with a second picking approximately 3 wk later. This interval varied due to weather and scheduling at each location. Percent lint was determined by combining seed cotton subsamples of individual treatments across replications and ginning on a 20-saw gin with dual lint cleaners. Lint yields were calculated by multiplying the lint fraction by seed cotton weights. Total lint yields were calculated by adding the first- and second-harvest lint yields for each treatment. The treatment effect on earliness of maturity was evaluated as the percentage of total yield picked at first harvest (Richmond and Ray, 1966).

Statistical analyses of lint yields and maturity (earliness) were performed utilizing mixed model SAS procedures (SAS Inst., 1997). The mixed model procedure provides Type III F statistical values but does not provide mean square values for each element within the analyses or the error terms for mean separation. Therefore, mean separation was evaluated through a series of protected pair-wise contrasts among all treatments (Saxton, 1998). A probability level of 0.05 was used for mean separation of planned comparisons. These analyses include treatment effects on both N rates and application methods on yields. Because separation of placement effects on yields was difficult for certain years, broadcast and injected yield response functions were developed through regression analyses for each location and were tested for significant differences using F-test (Chow tests) (Kennedy, 1992, p. 108–109). The Chow Test is an F-test with T₁ + T₂ - 2K degrees of freedom and it takes the form:

where T₁ and T₂ are the number of observations in each of the regressions we are comparing and K is the number of variables in each regression including the intercept; SSE (unconstrained) is the sum of the SSEs when the two regressions are performed separately; and SSE (constrained) is the SSE from performing one regression using all the data from both regressions. The latter regression using all the data essentially constrains the parameters for both situations to be equal.

	Results

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Experiment duration for the three locations varied between 2 and 4 yr with each location having different winter cover crops. The yield data as affected by N treatment will be presented by location and winter cover. Reference to N treatment is inclusive of the 11 treatments (N rates and application methods); otherwise, specific treatment effects will be identified and presented.

Loring Silt Loam (Winter Annuals)
The N treatment (rate-placement) effects on lint yields of cotton produced on Loring silt loam were highly significant (P < 0.0001) but inconsistent across the 4 yr, as indicated by a year x N treatment interaction (Table 1).

View this table: [in this window] [in a new window]   Table 1 ANOVA using mixed model F statistical values for evaluating N treatments (rates and application methods) on lint yields, and maturity of no-till cotton produced on three soils.

Cotton yield response functions estimated for broadcasting and injecting the two N sources are presented in Table 3. The F-tests (Chow test) indicate that the yield response coefficients for the broadcasting AN and injecting UAN functions were similar in 1994, 1996, and 1997. In 1995, broadcasting AN resulted in higher yields than injecting UAN. For the annual response functions, the yield increase with increased N rate (slope) was higher for broadcasting AN in 1995 relative to injecting UAN, but these differences were not significant in other years.

Pair-wise contrasts show that 2-yr average lint yields were increased by broadcasting AN up to 101 kg N ha^-1 (Table 2). However, yields were reduced by injecting UAN at either 67 or 134 kg N ha^-1 compared with broadcasting AN. Splitting the AN application resulted in yields similar to broadcasting 101 kg N ha^-1 as AN.

The coefficients of yield response functions for broadcasting AN and injecting UAN were not different (Table 3). Again, the regressed equation slopes show that the yield increase with increased N rate was similar for broadcasting AN as for injecting UAN.

Lexington Silt Loam (Small Grain Cover)
The N treatments had a significant effect (P < 0.0001) on lint yields of NT cotton produced on the Lexington silt loam (Table 1). As was observed for cotton produced on the Loring silt loam, treatment effects were inconsistent over the 2 site-years as showed by the year x N treatment interaction.

The 1996 pair-wise contrasts show yields produced on this soil were increased by either broadcasting AN or injecting UAN at 34 kg N ha^-1, but higher rates did not significantly increase yields. Injecting 134 kg N ha^-1 as UAN reduced yields relative to broadcasting or split applying AN at 134 kg N ha^-1. In 1997, split applying 101 kg N ha^-1 as AN resulted in higher lint yields compared with broadcasting AN or injecting UAN at planting. Broadcasting AN at 67 kg N ha^-1 resulted in higher yields relative to injecting UAN.

Coefficients of the two yield response functions for either broadcasting AN or injecting UAN were not different for either 1996 and 1997 (Table 3). Once again, yield increases with increased N rate for these two yield functions (slope) were similar for broadcasting AN compared with injecting UAN.

Effect of Application Methods on Earliness of Maturity
The N treatments had a highly significant effect on earliness of cotton produced on the three soils (Table 1). The effect of these treatments on earliness was consistent across years for the Memphis and Lexington soils but not the Loring soil as indicated by the year x N treatment interaction.

In 1994, earliness of cotton produced on the Loring silt loam was reduced by injecting UAN at 101 kg N ha^-1 compared with broadcasting AN but was similar at other rates (Table 4). Earliness was not affected by increased N rate. In 1995, injecting UAN at 67 kg N ha^-1 reduced earliness compared with broadcasting AN, while the reverse was observed when AN was broadcast at 134 kg N ha^-1. Earliness was reduced by applying the higher N rates regardless of application method. Injecting UAN reduced earliness in 1996 at all application rates compared with broadcasting AN. Again, earliness was reduced by applying the higher N rates regardless of application method. Differences in earliness due to N application method were not observed in 1997.

The pair-wise contrasts indicate earliness differences due to the two application methods (broadcasting AN and injecting UAN). Regressed yield equations were developed and compared to evaluate first-harvest differences between broadcasting AN and injecting UAN (Table 5). Evaluation of the two yield response functions for cotton produced on the Loring silt loam indicates coefficient differences in 1995 and 1996 with no differences in 1994 and 1997. These differences were not observed for total yields, except for 1995 (Table 3). Response coefficient differences between broadcasting AN and injecting UAN were also observed for cotton produced on the Memphis silt loam and the 1996 yields produced on the Lexington silt loam (Table 5). For the three locations, the regressed coefficients for broadcasting AN were greater than for injecting UAN in 5 of the 8 site-years.

	Discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

Split N applications increased yields only 1 of the 8 site-years. Unfortunately, the split N rates (101 and 134 kg N ha^-1) may have been too high for this research. Because of the limited frequency of yield response (1 yr in 8) in this research, split N application for cotton production is questionable due to the expense involved with the extra trip over the field and equipment costs.

Injecting N delayed crop maturity in some site-years compared with broadcasting AN. Several factors can be speculated for this delayed crop maturity. One factor may be the difference in N sources (UAN and AN) and application method (injected vs. broadcast). The injected UAN source contains 25% NH₄–N and 50% NH₂–N, whereas AN contains 50% NH₄–N. The conversion of urea-N to NO₃–N may require more time than the conversion of AN–N to NO₃–N. An additional factor that may affect earliness is possibly greater N concentration resulting from the injection application method (Howard and Essington, 1998). Surface broadcasting N over the soil increases the probability of N immobilization by microbial activity reducing N concentration, at least temporarily. Injecting UAN reduces N immobilization and should provide a higher N concentration within the restricted application zone. Increased N concentration from broadcasting higher N rates has been reported to delay cotton maturity and reduce yields (Boquet et al., 1994; Hutchinson et al., 1995; Maples and Keogh, 1971; McConnell et al., 1993; McConnell et al., 1995).

Crop maturity is a critical production consideration for cotton producers along the northern edge of the U.S. Cotton Belt (Gwathmey and Howard, 1998). Practices that delay maturity often reduce yields because of reduced heat-unit (DD60) accumulation during the latter part of the growing season. For instance, crop maturity of cotton produced on the Lexington silt loam was reduced both years by injecting the N. The accumulated DD60s between planting and first harvest were 2195 and 2190 for 1996 and 1997, respectively. In 1996, a total of 27 DD60s were accumulated between first and second harvest periods. In 1997, only one DD60 was accumulated between first and second harvest periods. Heat-unit accumulation for the three soils was similar, and data for the remaining two are not reported. Limited heat-unit accumulation in this region indicates the need to identify treatments that are conducive to earliness. However, treatments that delay cotton maturity and promote higher second-harvest yields may be desirable for producers in areas having a greater heat-unit accumulation potential after first harvest.

	Conclusions

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 
Broadcasting N as AN was a satisfactory application method for NT cotton production on three loess-derived soils having different winter covers. Lint yields were maximized by applying 67 kg N ha^-1 on the Loring and Lexington silt loams but 101 kg N ha^-1 was required to maximize yields on the Memphis silt loam. Lint yields were greater in 1 of 8 site-years from broadcasting AN compared with injecting UAN. Split N applications of AN resulted in higher yields in only 1 of 8 site-years relative to broadcasting AN at planting. The extra time and expense of the split N applications or injecting N do not justify the added time and expense for cotton production on these soils. Crop earliness (maturity) was improved from 79.0 to 82.7% first-harvest on average, across the 8 site-years by broadcasting N compared with injection. This may improve the likelihood that cotton can be harvested before a killing frost along the northern edge of the U.S. Cotton Belt.

	ACKNOWLEDGMENTS

 
The authors acknowledge the cooperation of the Ames Plantation staff under terms of a perpetual trust to the University of Tennessee by Julia C. Ames. We also acknowledge the staff members located at the Milan Experiment Station, Milan, TN, and the West Tennessee Experiment Station, Jackson, TN, for their cooperation and efforts in this research.

Received for publication January 26, 2000.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion Conclusions REFERENCES

 

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