NITROGEN-FERTILIZATION OF COTTON CULTIVARS OF DIFFERING MATURITY

Management of N nutrition of cotton (Gossypium hirsutum L.) is one of the most critical aspects of successful cotton production, but growth and yield responses of individual cotton cultivars to N fertilization is relatively unknown. The objective of this research was to evaluate the responses of three cotton cultivars (Arkot 518, Stoneville 453; and Deltapine 90) to soil-applied N fertilization rates. The study was conducted for 3 yr on a Hebert silt loam soil (fine-silty, mixed, thermic Aeric Ochraqualf). Few significant (alpha = 0.05) cultivar x N rate interaction differences were found, although main effects of the N treatments and the cultivars were evident. The most pronounced responses of the cotton were found as an effect of the N-fertilization treatments. Nitrogen rates in excess of 112 kg N ha(-1) did not significantly increase seed cotton yields in any year of the study. The mean yield of the cultivars among N rates was significantly different in only one year of the study. Earliness of the cotton was reduced by increasing N rate, as indicated by significant differences in nodes above white flower (NAWF) measurements. Significant differences were also found in the NAWF measurements for the cultivars, thereby inferring maturity differences among the cultivars tested. Of the cultivars evaluated, Arkot 518 was earliest, followed by Stoneville 453, and then Deltapine 90. Significant interactions of cultivar and N rate were found only in three dates of NAWF (1991), and one date of petiole NO3--N content (1940). Soil samples taken after 3 yr of continuous fertilization treatments showed a significant NO3--N accumulation at the 15- to 45-cm depth only in plots treated with 224 kg N ha(-1).