Nutrient runoff from North American grasslands

Authors: HARMEL, DAREN - Former ARS Employee; MOTT, JOSHUA - Former ARS Employee; Schantz, Merilynn; Hoover, David; Augustine, David; HIRD, AARON - Natural Resources Conservation Service (NRCS, USDA); Kleinman, Peter; Porensky, Lauren; RITTEN, J - Colorado State University; STACKHOUSE-LAWSON, K - Colorado State University

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2026
Publication Date: 6/29/2026
Citation: Harmel, D., Mott, J., Schantz, M.C., Hoover, D.L., Augustine, D.J., Hird, A., Kleinman, P.J., Porensky, L.M., Ritten, J., Stackhouse-Lawson, K. 2026. Nutrient runoff from North American grasslands. Rangeland Ecology and Management. 108:66-74. https://doi.org/10.1016/j.rama.2026.05.006.
DOI: https://doi.org/10.1016/j.rama.2026.05.006

Interpretive Summary: Grasslands encompass nearly 40% of the terrestrial earth’s surface, yet their contribution to N and P runoff and to adverse water quality impacts has not been systematically evaluated. To address this need, we utilized 1412 site-years of data from 41 studies in the MANAGE database to quantify annual nutrient loads in runoff from grasslands in the Continental US and Canada. We calculated summary statistics for several potential factors, including ecoregion, grassland type, land use/grazing management, and fertilizer type and conducted more in-depth analyses related to land use/grazing management. Noteworthy results include: 1) Ecoregion had a significant impact on all mean annual N and P loads with the exception of particulate P, and the highest loads typically occurred in the Southeastern USA Plains; 2) Improved pasture both with and without overseeding had higher mean annual dissolved and total N and P loads than native sites; 3) Despite lower fertilizer rates and increased nutrient uptake potential by cover crops, improved pasture with overseeding did not consistently lose less N and P in runoff than improved pasture without overseeding; 4) Mean annual particulate N and P loads occurred in the following order: Continuous grazing at heavy intensities > continuous grazing at light-moderate intensities ˜ rotationally grazing > ungrazed ˜ hayed land; and 5) “Organic only” fertilization produced the highest dissolved and total N and P loads, likely due to high animal manure application rates as such occurs on waste application fields. These results, presented for the first time in a compilation across North American ecoregions, provide insights into climatic, land use, and management impacts of nutrient runoff losses to guide programmatic, policy, and management decision-making.

Technical Abstract: Grasslands encompass nearly 40% of the terrestrial earth’s surface, yet their contribution to N and P runoff and to adverse impacts such as accelerated eutrophication has not been systematically evaluated. To address this need, we utilized 1412 site-years of data from 41 studies in the MANAGE database to quantify annual nutrient loads in runoff from grasslands in the Continental US and Canada. We calculated summary statistics for several potential factors, including ecoregion, grassland type, land use/grazing management, and fertilizer type and conducted more in-depth generalized linear mixed model (GLMM) analyses related to land use/grazing management. Noteworthy results include: 1) Ecoregion had a significant impact on all mean annual N and P loads with the exception of particulate P, and the highest loads typically occurred in the Southeastern USA Plains; 2) Improved pasture both with and without overseeding had higher mean annual dissolved and total N and P loads than native sites; 3) Despite lower fertilizer rates and increased nutrient uptake potential by cover crops, improved pasture with overseeding did not consistently lose less N and P in runoff than improved pasture without overseeding; 4) Mean annual particulate N and P loads occurred in the following order: Continuous grazing at heavy intensities > continuous grazing at light-moderate intensities ˜ rotationally grazing > ungrazed ˜ hayed land; and 5) “Organic only” fertilization produced the highest dissolved and total N and P loads, likely due to high animal manure application rates as such occurs on waste application fields. These results, presented for the first time in a compilation across North American ecoregions, provide insights into climatic, land use, and management impacts of nutrient runoff losses to guide programmatic, policy, and management decision-making.