Effect of Nitrogen Fertility Rates on Cotton Crop Response to Cotton Fleahopper Damage

A 3-year field study evaluated the effect of artificial injury to cotton squares mimicking acute cotton fleahopper damage under variable nitrogen application rates on cotton fiber yield and quality. The experiment was laid out in a split-split-plot randomized block design with five nitrogen fertility rate treatments applied for 15-17 years as main plots (16-row plots), split into two 8-row sub-plots: 1) nitrogen applied annually as previous years, and 2) nitrogen not applied since 2016, and two artificial cotton square injury treatments mimicking acute cotton fleahopper infestation as sub-sub-plots with four replications (total 80 experimental units). Within each of the five main-plot treatments that included pre-bloom side-dress applications of augmented N fertilizer rates of 0, 50, 100, 150, and 200 lb N/acre for 16 years, sub-plot treatments included N augmentation using a soil applicator injection rig versus no N augmentation. Considerably higher residual soil nitrogen was recorded from plots that received the two highest N rates in preceding 16 years. Withdrawing of N following 16 years of continuous augmentation resulted in lower leaf N and slightly lower lint in all N rate treatments. Removal of 100% squares 3-week into squaring did not significantly impact lint yield at lower N levels, but the yield was reduced by 20-30% at the two highest N levels; greater impact of square removal was observed on N-withdrawn plots compared to that in continuous N augmented plots.