A group of researchers from Iowa State University and the National Soil Tilth Laboratory in Ames, Iowa, have studied the amounts of sediment and phosphorus in runoff as related to grazing management.

The pasture experiment included three blocks of five 1-acre paddocks grazed by beef cows over the course of three years. Management for the five paddocks ranged from ungrazed control to rotational stocking with different sward heights. At four times throughout the growing season, rainfall simulations were conducted and runoff was collected from all paddocks and analyzed for total sediment, total P, and total soluble P.

“Our results showed that losses of sediment, total P and total soluble P were generally greater from grazed paddocks than ungrazed paddocks,” says Jim Russell, ISU animal science professor who participated in the study. However, losses from paddocks with two of the grazing-management treatments did not differ from ungrazed paddocks. These two treatments included a rotational stocking to sward height of 4 inches, and the other harvested as hay during the summer and grazed during the winter.

These results imply that managing rotational stocking to maintain adequate sward height and/or using vegetative buffer strips along pasture streams may reduce sediment and phosphorus losses in pasture runoff. Information about this study is at the Iowa Beef Center’s Forage & Grazing resource, www.iowabeefcenter.org