Citation:

Compton, J., S. Pearlstein, L. Erban, R. Coulombe, B. Hatteberg, A. Henning, J. Renee Brooks, AND J. Selker. From field to groundwater: Quantifying crop N budgets, performance metrics and nitrate leaching in the southern Willamette Valley, Oregon. Pacific and Mountain West Nutrient Cycling, Soil Health and Food Safety Virtual Conference, Virtual Conference via Zoom, Virtual Conference, October 27 - 29, 2020.

Impact/Purpose:

Nitrate contamination of groundwater is an important issue in many agricultural areas across the country. Nutrient best management practices are needed in these areas to allow for sustainability of agriculture and water quality. In 2013, a team of researchers from EPA, Oregon Department of Environmental Quality, Oregon Department of Agriculture, local Soil and Water Conservation Districts, and USDA-NRCS were funded a RARE proposal to study nutrient management in production agriculture in one of Oregon's Groundwater Management Areas (GWMA), established due to high nitrate concentrations in drinking water sources. This RARE project supported a four-year study examining nitrate leaching in production farm fields, collaboratively with local farmers, to understand the actual rates of nitrate leaching from production farming. This team uses the data on N leaching, fertilizer application and yield to develop a set of benchmarks that can be used to better understand agricultural N management.

Description:

Nitrate leaching is a direct and important, yet difficult to measure, contribution to contamination of groundwater and surface waters in agricultural areas. This study examines fourteen farm fields over a four year period (2014-2017), providing over fifty sets of annual, field-level performance metrics related to nitrogen (N), including inputs, crop outputs, N use efficiency (NUE), nitrate-N leaching and surplus N remaining after crop harvest from agricultural crops in the southern Willamette Valley. Leaching varied widely across the study area; crop-specific average nitrate-N leaching losses ranged from 10 in hazelnuts to over 200 kg N ha-1yr-1 in peppermint. Most of the leaching occurred during the fall. We used a graphical approach to explore the relationships among N surplus, crop N output and NUE that allowed us to examine crop differences in a standardized way. For example, the blueberry site had high inputs and surplus, while peppermint had not only high inputs but also high crop N removal and NUE, and, thus, lower N surplus. Most wheat crops had high NUE and evidence of soil N mining, and grass seed crops had intermediate values for N inputs, surplus and removal. Annual N inputs and surplus generally were not well correlated with leaching losses, suggesting that leaching varied more with specific crop type and management in this area. Grass seed and hazelnuts, the dominant crop types in the southern Willamette Valley, were intermediate in terms of NUE, N leaching, and surplus. While the overall NUE across all fields was 57%, variation among fields was substantial and consideration of multiple metrics (NUE, and N leaching, harvest and surplus) may best inform efforts to improve groundwater quality and agricultural sustainability.

Record Details: