Improving Nitrogen Recommendations for Winter Wheat In Arkansas.

The recent success of N-ST*R- the N soil test for rice has led to the development of a soil-based N test for winter wheat in Arkansas. Current N rate recommendations for winter wheat in Arkansas are based on a combination of soil texture and previous crop. During the past five years N rate trials have been conducted on silt loam soils across the state of Arkansas to determine the ability of alkaline hydrolyzable- N (AH-N) to correlate with wheat TN uptake, percent relative grain yield (RGY) and calibration of AH-N to predict N needs for wheat. Soils were sampled in 15 cm increments to 60 cm and analyzed for AH-N by either the Illinois Soil N Test (ISNT) or Direct Steam Distillation (DSD).  Wheat TN uptake was highly correlated (>0.68, p<.001) with both the ISNT and DSD at the 0-15 cm depth, indicating the relationship between AH-N and plant available N were closely linked. Results also exhibited a strong correlation between percent relative grain yield and ISNT and DSD at the 0-15 cm depth. Calibration of N rate to achieve 95% RGY at the 0-15 cm depth, resulted in a coefficient of determination >0.75 for both methods. The results of this work are the first step in developing site-specific N fertilizer rate recommendations for winter wheat, and will help to improve the long-term sustainability of Arkansas winter wheat production.