Improved N Management In the Dryland Pacific Northwest Winter Wheat Summer Fallow System.

Nitrogen (N) fertilizer is a major expense for wheat growers. More accurate N recommendations will reduce input cost and maximize economic return in the winter rainfall dryland region of the Pacific Northwest. Growers apply N based on average precipitation and yields but variation in annual precipitation means that excessive N is applied in ‘dry’ years increasing cost. Conversely, in ‘wet’ years, the N application rate is insufficient to permit the crop to maximize the yield potential. One approach to increase the accuracy of N applications is to apply a ‘base’ rate of N in the fallow phase that would be sufficient to supply the crop N requirement in a ‘dry’ year. Then, additional N could be applied in the early spring of the crop year when more is known about the total precipitation and yield potential. However, there is little information available on the effect of split applications on the grain yield and protein, the effectiveness of the various N fertilizers that could be used, and the optimum application method and time of application in the spring. Spring N applications were made by broadcasting urea or applying UAN 32 solution with a dribble band, broadcast spray, or spike wheel applicator at either tillering or stem elongation at three N rates. Increasing N application rates increased grain yield and protein but there were no consistent differences in grain yield or protein between the sources or times of application.