Precision Nitrogen Management: Evaluating Management Zones and Optimizing Nitrogen Rates in Dryland Winter Wheat.

Site-specific or precision nitrogen (N) management is proposed as a strategy to improve fertilizer use efficiencies. Current fertilizer recommendations for the dryland cropping systems of the inland Pacific Northwest (PNW) are based on uniform, whole-field applications. Studies at the WSU Cook Agronomy Farm have documented the inefficiencies of this recommendation system. Unused N represented by low nitrogen use efficiencies (NUE) is a financial loss to growers and can contribute to the degradation of water and air quality. Currently, recommendations to farmers in the PNW region are largely lacking for site-specific N management as science-based decision support, monitoring, and evaluation systems are not well established. The goal of this study is to continue development of science-based decision support systems for farmers that want to implement precision agriculture technologies in their N fertilizer applications. First the effectiveness of current management zones based on relative yield, soil type, and apparent electrical conductivity (ECa) will be evaluated. Evaluations will assess grain yield, protein, NUE, and in-season N status of areas treated with variable rate N application as compared to areas treated with uniform rate applications. Second, a 20 acre on-farm study was established near Walla Walla, WA. An Exactrix variable rate applicator was used to apply five different N rates across the field. Spatial variability in wheat response will be analyzed at the different N rates and compared to the spatial variability in soil and terrain factors. Nitrogen response curves will be generated to find optimal N rates for winter wheat at different field locations. Third, because of the breadth of already existing data at the WSU Cook Agronomy Farm, data from this site will be used to perform similar analyses as those mentioned for both the Wilke Extension Farm and on-farm site near Walla Walla, WA.