Evaluation of Foliar UAN and Timing on Grain Yield and Nitrogen Concentration in Winter Wheat (Triticum aestivum L.).

Several studies have investigated the effects of foliar nitrogen (N) timing on grain yield and protein in hard red winter wheat (Triticum aestivum), yet results remain inconclusive. The objective of this study was to evaluate grain yield and grain protein response to foliar nitrogen application. Four field trials were planted in 2014 and 2015 in Oklahoma. Urea ammonium nitrate (UAN, 28-0-0) mixed in a 1:1 solution with water was foliar applied at Feekes growth stages 4 and 10. Four treatments consisting of three rates of nitrogen (14, 28, and 40 kg N ha^-1) were applied when most tillers were formed (Feekes 4), and 14 kg N ha^-1 was applied when the head was developed (Feekes 10). A control plot (0-N applied) was also evaluated. In 2014, no pre-plant fertilizer N was applied. In 2015, urea (45 kg N ha^-1) was applied pre-plant in all plots except the control, totaling 6 treatments. Application of 40 kg N ha^-1 at Feekes 4 promoted an increase in grain nitrogen concentration in Stillwater and Hennessey. Also, application of 14 of kg N ha^-1 at Feekes 10 increased grain protein in Hennessey. Low rates of foliar N did not result in significant leaf burn. While foliar N did not increase grain yield, it did  grain nitrogen at 2 of 4 sites.