Site-Specific Wheat Density and Applied N: Optimizing Yield and Nitrogen Use Efficiency.

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 a framework that can lead to improvements in Nr use efficiency. 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 conditions and to develop the concept of PA for use in sustainable agroecosystems and science-based Nr policy.

Nitrogen and plant density field trials with winter wheat (Triticum aestivum L.) were conducted at the Washington State University Cook Agronomy Farm near Pullman, WA under long-term no-tillage management in 2010 and 2011. Treatments were imposed across environmentally heterogeneous field conditions to assess soil, crop and environmental interactions. Microplots with a split N application using 15N-labeled fertilizer were established in 2011 to examine the impact of N timing on uptake of fertilizer and soil N throughout the growing season for two plant density treatments. Preliminary data show that plant density manipulation combined with precision N applications resulted in greater wheat yield with less seed and N inputs. 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.