Evaluation of N Fertilizer Rate and Timing on Wheat Yield

Series/Report Number: COARC2015

Abstract: This project sought to evaluate the effects of N rate and timing on yield and grain protein content in irrigated winter wheat grown in central Oregon. Currently, many wheat producers in the area apply N fertilizer in the fall, rather than in the spring, due to logistical concerns of weather, soil moisture, and workload. By evaluating the effect of fall and spring applications of N, we aim to provide guidance for growers on when to apply N fertilization in an effort to maximize grain yield. Large-scale plots were used to assess N rate and timing effects on grain yield, test weight and protein percentage. To trace the fate of fertilizer N, 15N labeled urea was applied to micro-plots in fall and spring, and soil and biomass samples were collected and analyzed to track recovery of the 15N labeled urea. Winter wheat grain yield for 2013-14 and 2014-15 where soil test N was high was largely unresponsive to N fertilization. The labeled 15N urea was recovered primarily from the top six inches of soil and losses ranged from 0 to 30% in 2013-14. Winter wheat response to N fertilization in central Oregon is highly variable likely due to variation in soil depths and textures as well as soil N supply related to crop rotation.