In a previous blog post, I introduced a project about using nitrogen (N) rich reference zones in wheat. The goal of the project is to show how N-rich reference zones can be used to guide N fertilization in small grains, to increase crop productivity and N use efficiency. This is a three-year project funded by the CDFA Fertilizer Research and Education Program, and UCCE has implemented several demonstration sites, including a site in the Delta. As we move into the 2021-22 wheat season, I wanted to provide an update on the project and share that we have published case studies about the Delta site. The purpose of the case studies is to describe how local conditions influenced how we used N-rich reference zones to guide N management.

The N-rich reference zone is a small area within a field where extra N fertilizer is added at the beginning of the season. This extra fertilizer ensures that the reference zone will not be N-limited after planting. Reference zones are most useful to growers who can apply the majority of their seasonal N budget during or after the tillering stage of growth. Previous work has shown that in-season N applications can improve yield and/or protein under some conditions. When a grower is determining whether and how much N fertilizer to add in-season, measurements from both the reference zone and the broader field are compared to understand whether the broader field is sufficient in plant-available N.

We have used a soil nitrate quick test (SNQT), handheld canopy reflectance devices, and drone and satellite imagery to evaluate the N status of the reference zones and the broader field. The SNQT is performed in the field and provides a quick, inexpensive estimate of nitrogen availability in the soil. The proximal and remote sensing allow us to see differences in green vegetation that the human eye cannot detect. We collect data from both the N-rich zones and the broader field, and then we can evaluate N sufficiency in the field relative to the N-rich zone. Our team has also developed a N Fertilizer Management Tool, which can help with in-season N fertilizer decision making.

At the Delta location on Tyler Island, we have trialed these practices on high organic matter soils. In the 2020-2021 wheat season, we found that the additional fertilizer in the N-rich zones did not improve wheat yield at this site. We did find, however, that in-season N fertilizer improved wheat protein by about 0.5 percent. More details can be found in the case study.

Implementing N-rich reference zones allows growers to get real-time knowledge to inform N fertilizer management in small grains. This information can help them make fertilizer applications when increased yield and/or protein benefits are likely and avoid them when they are not. Please visit the UC small grains website for more information about N management practices and to read case studies from other statewide demonstration sites. Don't hesitate to reach out to me if you would like more information on how to implement N-rich zones in your fields this season.