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.