Precision Agroecology: Management of Wheat Density to Optimize Nitrogen and Water Use.

Rising levels of reactive nitrogen (Nr) in the environment coupled with increasing population positions agriculture as a major contributor for supplying food and ecosystem services to the world. The concept of Precision Agroecology (PA) explicitly recognizes the importance of time and place by combining the principles of precision farming with ecology creating the potential to improve Nr use efficiency and inform policy. In the Palouse region of the Pacific Northwest, USA, relationships between productivity, N dynamics and cycling, water availability, and environmental impacts result from intricate spatial and temporal variations in soil, ecosystem processes, and socioeconomic factors. Our research goal is to investigate N use efficiency (NUE) in the context of factors that regulate site-specific environmental and economic processes and to develop the concept of PA for use in sustainable agroecosystems and incentive-based Nr policy.

Nitrogen and plant density field trials with winter wheat (Triticum aestivum) were conducted at the Washington State University Cook Agronomy Farm near Pullman, WA under long-term no-tillage management. Treatments were imposed across an environmentally heterogeneous field (15 ha) to assess soil, crop and environmental interactions. Preliminary data show that over the entire field, precision N management resulted in applying 62% less (64 kg ha-1) N while improving yield by 794 kg ha-1 compared to conventional uniform N management (103 kg N ha-1). Plant density manipulation combined with precision N applications indicated that seeding rate reductions could maintain or increase yield. These findings indicate that improvements to NUE and agroecosystem sustainability should consider landscape-scale patterns driving productivity (e.g., spatial and temporal dynamics of water availability and N transformations) and would benefit from policy incentives that promote a PA approach.