ABSTRACT
The effects of two nitrogen (N) fertilizer rates and four defoliation applications on cotton yield and quality were determined at two test sites located at the Tennessee Valley Substation in northern Alabama. Results were compared to those predicted by the Gossym Comax cotton computer model. The test sites were planted two weeks apart and the normal N fertilizer rate for the area (70lb/A) was compared to the N fertilizer rate recommended by Gossym-Comax. In this study, Gossym Comax cotton plots received N fertilizer at the rate of 70lb/A preplant, 30lb/A sidedress and 20lb/A foliar. All the cotton was non-irrigated. To pin-point the optimum defoliation date, cotton was defoliated at three to four day intervals beginning one week before the defoliation date predicted by Gossym-Comax. Cotton yields decreased slightly, but not significantly, by the addition N fertilizer recommended by Gossym-Comax. The different defoliation applications also did not significantly affect cotton yields. Cotton length and strength measurements were not affected by defoliation or N fertilizer applications. However, lint percentage and micronaire readings were reduced by the additional N applications above 70lb/A. In these tests, Gossym-Comax over-estimated the N fertilizer requirements of the non-irrigated cotton. Also, Gossym-Comax was one to over two weeks late in predicting defoliation which was caused by Gossym-Comax not terminating cotton growth when the severe drought conditions occurred in late July and August.
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