RICE CULTURE Validation of the Nitrogen Soil Test for Rice (N-STaR) on Clay Soils in Arkansas

The development of the Nitrogen Soil Test for Rice (N-STaR) allowed site-specific nitrogen (N) recommendations for rice on silt loam soils in Arkansas. Expansion of the site-specific N test into clay soils and its use in 27 counties in Arkansas necessitated the validation of N-STaR for rice produced on clay soil. In 2014, 6 sites across Arkansas were selected for their wide difference in native soil-N and planted to one of three rice cultivars. Stands were monitored for disease and pest pressure and yields were measured at the end of the season. Soil samples were taken at a 12-inch depth, analyzed using the N-STaR method, and the site-specific N rates were predicted using the calibration curves for 95% and 100% relative grain yield (RGY). In the validation trial, six treatments were compared; a control (0 lb N/acre); the N-STaR 95% and 100% RGY N-rates applied in a standard two-way split (2-WS) application with 45 lb N/acre applied at beginning internode elongation and the remainder preflood; the N-STaR 95% and 100% RGY N-rates applied in a single preflood (SPF) application; and the standard N recommendation based on soil texture and previous crop. Nitrogen rates predicted using N-STaR ranged from 50 lb N/acre to 210 lb N/acre. Rice yields obtained with the 95% RGY recommendation were statistically similar to the standard N-rate recommendation for all 6 sites and numerically greater at 2 of the 6 sites. For the 100% RGY recommendation, all 6 trials indicated similar yields could be achieved when compared to the standard N recommendation. This data indicates that N-STaR is able to predict site-specific N fertilizer rates for rice produced on clay soils over a wide range of environmental and production settings. AAES Research Series 626