A classification system for describing N-fertilizer performance in dryland wheat crops of the inland Pacific Northwest.

Wheat (Triticum aestivum L.) crops in the inland Pacific Northwest demand nitrogen (N) fertilizers at high levels to achieve yield and grain protein objectives. Inefficiencies in N use can accelerate soil acidification, contribute to NO emissions, and result in unnecessary input costs. Reducing N losses is a complicated problem, as producers have to consider grain protein and yield targets, co-limitations of water and other nutrients, longer term soil health goals, and variability in crop performance across fields. However, past work in the region has established that there are at least four prevalent N performance syndromes, each of which have different environmental effects and lend themselves to different actions for adapting N management. In this paper, we build on this work to develop a discrete six-class evaluation system that simplifies assessment of wheat N performance. We use over 20 years of harvest data from the Cook Agronomy Farm Long-Term Agroecosystem Research site to assess spatial and temporal patterns in wheat N performance. While some areas had durable high or low nitrogen performance, there was year-to-year variation due to weather, management, and cultivar-specific factors. For wheat management decisions, the categorical system narrows the range of possible problems, potential environmental effects, and solutions to poor wheat performance.