Predicting Nitrogen Use Efficiency and Grain Protein In Winter Wheat Using Greenseeker NDVI.

The algorithm presently used at Oklahoma State University for mid-season fertilizer recommendations uses predicted yield potential without additional N (YP0) and the response index (RI). The recommended N rate is calculated by subtracting N uptake without additional N from N uptake with additional N and dividing the difference by an assumed nitrogen use efficiency (NUE). To more accurately estimate NUE and thus improve nitrogen recommendations, Greenseeker and SPAD meter readings were evaluated for their use in predicting this parameter in Winter Wheat. Three winter wheat field experiments were established to evaluate NUE, grain protein, and N uptake as a function of rate and timing. Pre-plant treatments applied ranged from 28kg/ha to 227 kg/ha. Selected treatments also included top dress rates of 28, 57, 85, 113 and 142 kg N ha^-1.  Greenseeker and SPAD readings were collected at Feekes 3, 4, 5 and 7.  Results will show that NUE can be predicted early in the season and in time to adjust topdress N rates based on the expected NUE.