Nutrient Runoff From Agricultural Lands in North American Ecoregions

ABSTRACT Field‐scale runoff and water quality data are critical to understanding the fate of agricultural nutrients and mitigating their off‐site transport; however, regional influences such as precipitation, temperature, and prevailing cropping and management practices 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) in runoff from cropland and grasslands for North American ecoregions. Specifically, we analyzed annual N and P loads and the impact of land use, tillage, fertilizer timing, and fertilizer placement. Notable differences between ecoregions included: (1) 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 Semiarid Prairies (2.4 kg/ha) dominated by grasslands; (2) 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 (3) 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—that have never before been analyzed by ecoregion—should prove valuable for improving regional understanding of nutrient fate and transport and informing field‐scale agricultural management decisions.