Effect of Nitrogen Fertilization Practices on Spring Wheat Yield, Protein Content

Wheat response to nitrogen fertilizer management

IPNI-2012-USA-CA34

29 Apr 2016

2015 Annual Interpretive Summary


This study is evaluating the impacts of timing and rate of N fertilizer application on optimization of wheat grain yield and protein content while reducing the potential for N losses. This 4R–related study focuses on hard and durum classes of spring wheat grown in three regions in California over several years. Growers of hard and durum wheat are paid not only for crop yield but also for grain protein content. These factors can be inversely related and strongly influenced by the rate and timing of N fertilization. The goals of this research include improved understanding of interactions of N application timing and rate choices, and resulting productivity and protein content responses.

Field experiments are concluding for the second year of a three-year study in the San Joaquin Valley, the Sacramento Valley, and the Intermountain region. At the Sacramento Valley site, wheat receiving pre-plant applications of fertilizer use N less efficiently than crops that receive N applications at tillering and later. The apparent recovery of applied fertilizer N at a high yielding site in 2013-2014 in the Sacramento Valley at tillering and later resulted in >40% increase in apparent N recovery compared with pre-plant applications. At the San Joaquin Valley site, N applications at the boot and flowering stage had significant impacts on the protein content, but there were also interactions between application amounts and split application timing. At the Intermountain field site, wheat yields did not increase when N application rate exceeded 225 lb/A at tillering stage, but additional N increased yields when most N was applied preplant. Averaged over all N rates, the highest yield occurred when N was split between tillering and preplant applications. Significantly higher protein concentrations occurred when less N was applied preplant and more of the fertilizer application was delayed until the flowering stage. Soil analysis are underway to measure the residual nitrate present in the root zone in the various treatments and will be reported in the future.