Effects of Grazing Management on Sediment and Phosphorus Losses in Run-off (A Progress Report)

In 2001 and 2002, pastures at the ISU Rhodes Research and Demonstration Farm were grazed to determine the effects of stocking treatment on nutrient and sediment loss from pastureland. Treatments included an ungrazed control (UG), summer hay harvest with winter stockpiled grazing (HS), continuous stocking to a residual height of 2 inches (2C), rotational stocking to a residual height of 2 inches (2R), and rotational stocking to a residual height of 4 inches (4R). At three times in 2001 (late spring, mid-summer, and fall) and four times in 2002 (early spring, late spring, mid-summer, and fall), rainfall simulations were conducted at 6 sites within each paddock and 6 sites in a buffer zone down slope from each paddock. Run-off was collected and analyzed for total sediment, total phosphorus, and dissolved phosphorus. Simultaneous to each rainfall simulation, ground cover, penetration resistance, surface roughness, slope, contents of phosphorus and moisture of the soil, and the sward height and mass of forage were measured. In years 1 (late spring 2001 through early spring 2002) and 2 (late spring 2002 through fall 2002), mean concentrations of sediment in runoff did not differ between ungrazed or grazed paddocks. Mean concentrations of total P in the run-off were greater (P \u3c .05) in paddocks grazed to 2 inches by continuous or rotational stocking than in paddocks that were ungrazed, grazed to 4 inches by rotational stocking or harvested as hay and grazed as stockpiled forage. In year 1, mean losses of sediment, total P, and soluble P were greater (P \u3c .1) from paddocks grazed to 2 inches by continuous or rotational stocking than other treatments. In year 2, mean losses of sediment and total P in paddocks grazed to 2 inches by continuous stocking and mean losses of soluble P from paddocks grazed to 2 inches by rotational stocking were greater (P \u3c .05) than the other treatments