Citation:

Compton, J., S. Pearlstein, L. Erban, R. Coulombe, B. Hatteberg, A. Henning, J. Renee Brooks, AND J. Selker. Nitrogen inputs best predict farm field nitrate leaching in the Willamette Valley, Oregon. Nutrient Cycling in Agroecosystems. Springer Science and Business Media B.V. Formerly Kluwer Academic Publishers, New York, NY, , s10705-021-10145-6, (2021). https://doi.org/10.1007/s10705-021-10145-6

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. These metrics, combining information on nitrate leaching with yield, crop N output and other metrics, can provide the farm community and local organizations a way to compare agricultural and environmental performance of fields and crop types in the southern Willamette Valley GWMA.

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 harvest from agricultural crops in the southern Willamette Valley. Across the study area, leaching varied widely; crop-specific average nitrate-N leaching losses ranged from 10 kg N ha-1yr-1 in hazelnuts to over 200 in peppermint. Most of the leaching occurred during the fall. We used a graphical approach to explore the relationships between N surplus, crop N output and NUE, which allowed us to examine crop differences. For example, the blueberry site had high inputs and surplus, peppermint had high inputs but also high crop N removal and NUE and thus lower surplus, and most wheat crops had high NUE and evidence of soil mining. Annual nitrogen 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, leaching and surplus. While the overall NUE across all fields was 57%, variation between fields was substantial, and consideration of multiple metrics (leaching, harvest, NUE and surplus) will best inform efforts to improve groundwater quality and agricultural sustainability.

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