The Use of Plant Indices for In-Season Prediction of Cotton Lint Yield Response to Nitrogen Fertilization.

Nitrogen (N) fertilization has attracted concerns in many production systems. With the high cost of N fertilizers and the threat of N loss to the environment, increasing N use efficiency has become an important goal to maintain a productive and sustainable cotton industry.   The use of plant indices is an agricultural technique for refining N-fertilizer recommendations.  The study was initiated at three sites in northern Louisiana in 2008 to identify in-season plant indices that can be used to evaluate cotton lint yield response to N fertilizer.  These plant indices consisted of normalized difference vegetation index (NDVI), chlorophyll readings, plant height and leaf N which were taken at early square, early bloom, two weeks after early bloom, and four weeks after early bloom. The response of in-season plant indices has potential to relate to cotton lint yield response to N.  Two-weeks after early bloom showed the highest number of similar predictions, between lint yield and midseason plant indices, with 16 of 24 predictions.  However, earlier growth stages, such as early square and early bloom, show a similar number of predictions.  Plant height and NDVI were the plant indices that show the best accuracy at predicting cotton's lint yield response to N fertilization, with correlation coefficients values of 0.53 and 0.32, respectively.  The incorporation of two or more plant indices shows potential to increase the predictability of cotton's lint yield response to N-fertilization at the early growth stages.