Citation:

Compton, J., S. Pearlstein, L. Erban, R. Coulombe, B. Hattebery, A. Henning, J. Renee Brooks, AND J. Selker. Nitrogen inputs best predict farm field nitrate leaching in the Willamette Valley, Oregon. American Geophysical Union, New Orleans, Louisiana, December 13 - 17, 2021.

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 an important yet difficult to manage contribution to groundwater and surface water contamination in agricultural areas.  We examine 14 farm fields over a four year period (2014-2017) in the southern Willamette Valley, providing 53 sets of annual, field-level agricultural performance metrics related to nitrogen (N), including fertilizer inputs, crop harvest outputs, N use efficiency (NUE), nitrate-N leaching and surplus N.  Crop-specific nitrate-N leaching varied widely from 10 kg N ha-1yr-1 in hazelnuts to >200 kg N ha-1yr-1 in peppermint.  Averaging across all sites and years, most leaching occurred during fall (60%) and winter (32%).   Overall NUE was 57%.  We used a graphical approach to explore the relationships between N inputs, surplus, crop N harvest removal and NUE by crop type.  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 using soil N.  Annual N surplus was not well correlated with leaching, and leaching varied more by crop type and inputs.   Grass seed and hazelnuts, which are dominant crop types in the southern Willamette Valley, were intermediate in terms of NUE, leaching and surplus.  Of all performance metrics, N input was most closely aligned with field-level crop N harvest and nitrate leaching, therefore optimizing N inputs may well inform local efforts to reduce groundwater nitrate contamination.  

Record Details: