Influence of Pasture Stocking Method on Surface Runoff and Nutrient Loss in the US Upper Midwest

Grazing and hay forage crops reduce erosion compared to annual crops, but few studies have compared soil and nutrient loss among grazing systems compared to a control. We evaluated runoff water quality and nutrient loss among three grazing systems and a hay crop production field with manure application (control) using a paired watershed design. Four edge-of-field sites at a research farm in central Wisconsin were managed as hay during calibration (2013-2018) followed by a grazing treatment phase (2018-2020). Grazing treatments of different stocking methods included continuous stocking (CS), primary paddock stocking (PPS), and adaptive multi-paddock stocking (AMPS). Runoff, sediment, nitrogen (N), and phosphorus (P) loads were monitored year-round. Grazing increased average runoff volume by as much as 1.7-fold depending on stocking method and tended to decrease event mean N and P concentrations. CS had larger mean sediment (2.0-fold), total N (1.9-fold), and total P loads (1.2-fold) compared to the control and had the lowest average pasture forage mass. AMPS had lower N and P loss as a percentage of that applied from manure application/livestock excretion (1.3 and 1.6%, respectively) compared to the control (2.5 and 2.1%), PPS (2.5 and 2.6%), and CS (3.2 and 3.0%). Stocking method had a marked impact on nutrient loss in runoff from these systems, suggesting water quality models should account for pasture management, but nutrient losses from all perennial forage systems were small relative to previous data from annual cropping systems.