Another Step Forward: Validation of N-Star on Rice in Clay Soils in Arkansas.

Accurate N fertilization is vital to obtain high rice yields in Arkansas. The Nitrogen-Soil Test for Rice (N-STaR) was recently developed to estimate the N mineralization potential of a soil and provide site-specific N fertilizer recommendations. The N-STaR was validated on silt loam soils in Arkansas in 2013, but lacks validation on clay soils. Validation is an essential component in ensuring the accuracy of the N-STaR calibration curves. A total of 12 sites across Arkansas were selected on clay soils of varying native-N availability, soil samples were taken at each location, and N-STaR analysis was completed to determine the N rate using the 100 and 95% relative grain yield (RGY) curves. Six treatments were compared in the validation trial; a control (0 kg N ha^-1), the N-STaR 95 and 100% RGY N rates applied in a standard two-way split application (2-WS), the N-STaR 95 and 100% RGY N rates applied in a single pre-flood application (SPF), and the Standard N Recommendation (SNR) based on soil texture and previous crop. Season-total N rates using N-STaR resulted in N rate changes from -224 to 0 kg N ha^-1 when compared to the SNR. Nine of 12 locations had no statistical yield differences (α= 0.05) between the N treatments. At K-1, K-2, and B-2, there were no yield differences between the N-STaR 100% RGY treatments and the SNR while the N-STaR 95% RGY SPF was significantly different from the SNR with yield differences ranging from -1261 to -1917 kg ha^-1. Furthermore, the N-STaR 95% RGY 2-WS at K-1 yielded 1210 kg ha^-1 lower than the SNR. Overall, the N-STaR 100% RGY 2-WS and SPF applications and the N-STaR 95% RGY 2-WS application appear to accurately predict the N needs of rice in Arkansas, but the N-STaR 95% RGY SPF rate may require adjustment.