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Increase nitrogen rates in combination with plant growth regulators has been proposed for many years to enhance cotton production in the Mississippi Delta. Studies have been underway since 1987 to substantiate these recommendations with respect to both yield and quality. Nitrogen (N) rates of 60, 90, 120, and 150 lb N/A were band-applied prior to planting. The N was applied as urea-ammonium nitrate solution (32% N) to either side of the row. Pix (mepiquat chloride) was applied under different application systems which included an untreated control; 2 oz/A applied 4 times, 16 oz/A + 8 oz/A, 4 oz/A applied 4 times, and other systems which varied with seasons. The 2 oz/A and 4 oz/A rates of Pix were applied beginning at match-head square with the higher rates initiated at first bloom. In 1987, a compound designated as 'XE-1019' was included (0.25 lb ai/A) but later eliminated due to significant yield reductions in 1987 and residual carryover in 1988. The experiment consisted of 16 treatments arranged as a factorial in a randomized complete block and replicated 4 time. Each year, the plots were harvested twice with a spindle picker with subsamples removed at each harvest for ginning and the determination of lint percent. HVI measurements of quality were determined from each sample for 1989 through 1991. Statistical analysis by analysis of variance was used to determine significance for both yield components and quality measurements. Yield data was summarized for 1987 through 1991 with the XE-1019 plant growth regulator system eliminated from the combined analysis of main effects. Cotton yield was increased significantly with each additional 30-lb N increment up to 150 lb NA. However, percent lint decreased with increasing N rate. Thus, there was no significant increase in lint yield above 120 lb N/A. In all years, there was a significant increase in second harvest cotton at the higher N rates. Early data (1987 - 1989) indicated little response to the additional N above 120 lb?A even with the addition of plant growth regulators. In 1989, subsamples taken at harvest were ginned and used to evaluate the quality components. Micronaire, length, and Hunter's b value were found to be significantly altered by the higher N rates at both first and second harvest. At first harvest micronaire decreased from 4.26 to 4.19 when N rate was increased from 60 to 150 lb N/A. The length was increased slightly and the Hunter's b increased. Increases in Hunter's b are indications of increased yellowness and are not desirable. With second harvest cotton, the same trends were evident with reflectance (Rd) also being significantly higher at the 150 lb/A rate compared to the lower N rates. The plant growth regulator had little overall effect on yield and quality in this study. There was a very slight trend toward increased seed cotton where Pix was used. However, the lint percent was significantly lower where Pix had been used giving no response to the plant growth regulator applications regardless of the rate or system used. The only quality factors which were significantly affected by plant growth regulator were micronaire at first harvest. Micronaire decreased, length was increased and b value decreased. From the data collected over the last 5 years, increased N rates above 120 lb N/A even with plant growth regulators has not produced significant yield increases. |
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©National Cotton Council, Memphis TN |
Document last modified Sunday, Dec 6 1998
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