Nutrient runoff from agricultural lands in North American ecoregions

Authors: HOPKINS, A - Colorado State University; Harmel, Robert; IPPOLITO, J - Colorado State University; Kleinman, Peter; SHAOO, D - Clemson University

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2025
Publication Date: 2/20/2025
Citation: Hopkins, A.P., Harmel, R.D., Ippolito, J.A., Kleinman, P.J., Shaoo, D. 2025. Nutrient runoff from agricultural lands in North American ecoregions. Journal of the American Water Resources Association. 61(1). Article e70004. https://doi.org/10.1111/1752-1688.70004.
DOI: https://doi.org/10.1111/1752-1688.70004

Interpretive Summary: Field-scale runoff and water quality data are critical to understanding the fate and transport of nutrients applied to agricultural lands and minimize their off-site transport because it is at that scale that agricultural management decisions are typically made. However, regional influences such as precipitation, temperature, and prevailing cropping systems also impact nutrient runoff. In the present study, we used the recently-updated MANAGE database to conduct meta-type analyses of nitrogen (N) and phosphorus (P) runoff from cropland and grasslands for North American Level II ecoregions. Specifically, we analyzed annual N and P loads and the impact of land use, tillage, fertilizer timing, and fertilizer placement, and we observed several notable differences between ecoregions. For example, the Temperate Prairies dominated by highly erodible cultivated land had significantly higher median annual total N loads (11.7 kg/ha) than the South Central Semi-Arid Prairies (2.4 kg/ha) dominated by grasslands. Other notable results include: 1) corn production tended to produce higher N and P loads than other land uses in the Mixed Wood Plains, Southeastern USA Plains, and Ozark-Ouachita/Appalachian Forests; and 2) no-till had the highest dissolved P loads in the Southeastern USA Plains and Temperate Prairies, but conventional tillage had the highest dissolved P loads in the Ozark-Ouachita/Appalachian Forests. These data - never before compiled and analyzed by ecoregion - should prove valuable to improve regional understanding of nutrient fate and transport and to inform field-scale agricultural management decisions. Although these broad level, meta-type comparisons may produce over-generalized results, they are valuable for launching more in-depth analyses.

Technical Abstract: Field-scale runoff and water quality data are critical to understanding the fate and transport of nutrients applied to agricultural lands and minimize their off-site transport because it is at that scale that agricultural management decisions are typically made. However, regional influences such as precipitation, temperature, and prevailing cropping systems also impact nutrient runoff. In the present study, we used the recently-updated MANAGE database to conduct meta-type analyses of nitrogen (N) and phosphorus (P) runoff from cropland and grasslands for North American Level II ecoregions. Specifically, we analyzed annual N and P loads and the impact of land use, tillage, fertilizer timing, and fertilizer placement, and we observed several notable differences between ecoregions. For example, the Temperate Prairies dominated by highly erodible cultivated land had significantly higher median annual total N loads (11.7 kg/ha) than the South Central Semi-Arid Prairies (2.4 kg/ha) dominated by grasslands. Other notable results include: 1) corn production tended to produce higher N and P loads than other land uses in the Mixed Wood Plains, Southeastern USA Plains, and Ozark-Ouachita/Appalachian Forests; and 2) no-till had the highest dissolved P loads in the Southeastern USA Plains and Temperate Prairies, but conventional tillage had the highest dissolved P loads in the Ozark-Ouachita/Appalachian Forests. These data - never before compiled and analyzed by ecoregion - should prove valuable to improve regional understanding of nutrient fate and transport and to inform field-scale agricultural management decisions. Although these broad level, meta-type comparisons may produce over-generalized results, they are valuable for launching more in-depth, multi-factor analyses.