Refinement of Cotton Nitrogen Use Recommendations in Texas

Cotton lint yields have increased an average of 11 kg/ha/year over the past three decades, resulting in average yields going from 644 to 980 kg/ha.  Despite yield increases, most nutrient management recommendations were established decades ago and have not been re-evaluated since that time.  The higher yield potential of current cotton varieties indicates that nutrient recommendations may need to be adjusted. Furthermore, many N studies in the past have not considered all N inputs and outputs. Considering this, a more comprehensive approach is needed. This project analyzes a multitude of factors playing into N recommendations and will attempt refine them in two locations in Central Texas. This project also used multiple ways to understand N use including normalized difference vegetation index (NDVI), soil tissue analysis and yield.  Five rates of nitrogen (0, 45, 90, 135 and 180 kg N/ha) were applied in a randomized complete block design replicated four times. N attributing factors were quantified including litter residues and residual nitrate and ammonium at multiple depths (0-10, 10-30, 30-60 and 60-90 cm).