Nitrogen Recommendations for Rice in Arkansas Using the Illinois Soil Nitrogen Test and Direct Steam Distillation.

Nitrogen (N) response trials were conducted in Arkansas to evaluate the Illinois Soil Nitrogen Test (ISNT) and Direct Steam Distillation (DSD) in measuring soil N availability and as a tool for N fertilizer recommendations. Field studies were conducted on several silt loam soils at experiment stations and producer fields across the state. Six N fertilizer rates ranging from 0 to 202 kg N/hectare were applied in split applications in a randomized complete block design with four replications. Total N uptake and grain yield were used for correlation and calibration of each soil test. Percent relative grain yield and N fertilizer rate to achieve 95% relative grain yield was regressed against the mean ISNT and DSD values for the 0 kg N/hectare rate plots at each location. Currently, 24 site-years have been used to develop soil-based N tests for rice with significant relationships between the two soil tests and percent relative grain yield and N rate to give 95% relative grain yield.  Results show a strong correlation between percent relative grain yield and ISNT and DSD at the 0-45 cm depth. The coefficients of determination increased for percent relative grain yield and N rate to give 95% relative grain yield as depth increased until 45 cm, but then dropped significantly at the 0-60 cm depth. Coefficients of determination >0.80 for both methods at the 0-45 cm depth indicates the incorporation of either test for use in N fertilizer recommendations could improve N management for rice producers while lowering costs and environmental impacts.