Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/1994
Publication Date: N/A
Citation: Interpretive Summary: N use efficiency or the amount of fertilizer N taken up by winter wheat is typically low and ranges from 30 to 50% of the N applied. This N not taken up can replenish soil N but can also begin to saturate the system and cause N leaching. In addition increasing the available N in the soil may increase the protein content of the wheat grain, an undesirable consequence. If N were applied to wheat during both the fall and spring as a split application it might improve the amount of fertilizer used by the plant. We tested several different application combinations at different rates of fertilizer. It does appear that split applications of N are more efficient than a single dose of fertilizer in the fall. We now must investigate the technology that will allow efficient and economical split applications of fertilizer.
Technical Abstract: Nitrogen use efficiency (NUE) can be reduced by over fertilization, suboptimal yields and N losses. Nitrogen is typically fall-applied in eastern Washington for soft white winter wheat production, and is therefore subject to overwinter losses in deep soil layers. Increasing grain protein levels of winter wheat have been attributed in part to excessive N application rates and high residual N levels. Spring-N applications were evaluated over four site-years as an option to fall applied N for reducing N inputs and increasing N use efficiency. Nitrogen use efficiency was 26 to 44% lower in the high fall N treatment than the zero N control. Spring applied N maintained or increased N use efficiency compared to the fall rates. These results suggest spring N applications can improve fertilizer N recovery and N use efficiency over preplant applications in dryland winter wheat.