Evaluating End of Season Nitrogen Status in Rice.

Current N rate recommendations for rice in Arkansas are determined using the Nitrogen Soil Test for Rice (NSTaR). This soil test provides accurate recommendations for preflood-N applications by predicting the amount of N that will become plant available during the growing season. Considering the many potential N loss pathways in U.S. rice production system, N management is critical to producing a successful crop and maximizing profit. No quantitative test currently exists to determine whether N was managed properly throughout the season. There is a need for a post season test to quantify the amount of N in the plant at harvest to ensure the rice plant contained sufficient N to produce optimal yield. A study was conducted to evaluate the use of N concentrations in the stem of mature rice plants to determine whether insufficient, adequate, or excessive N was applied to the rice on a site-specific basis. In this study, six preflood N treatments ranging from 0 to 252 kg N ha^-1 were applied at two locations. Above ground biomass samples were taken at maturity and N concentrations were evaluated in nine stem segments starting from the soil surface and extending to 46 cm above the soil. These segments were analyzed for trends of N accumulation in order to select a consistent sampling height and appropriate sample size for an end of season N test. Results from this study will be used to develop procedures for a post season N evaluation in rice.