Summary and Implications
In order to quantify the sources of sediment, phosphorus (P), and pathogen loading of pasture streams, six 30-acre pastures, bisected by a stream, were stocked with 15 fall-calving cows from mid-May through midOctober of two years by continuous stocking with unrestricted stream access (CSU), continuous stocking with stream access restricted to 16-foot wide stabilized crossings (CSR), or rotational stocking (RS). Cows in RS pastures excreted less fecal P than cows in the CSU and CSR pastures. The proportion of water applied and the amounts of sediment and P in precipitation runoff during rainfall simulations were greater from bare sites on the stream banks of CSU or RS pastures than vegetated sites of CSU, RS, or CSR pastures. Amounts of stream bank erosion did not differ between grazing management treatments. When sources of sediment and P were compared, stream bank erosion contributed 99.5 and 94.4% of the sediment and P loading of the stream. At the stocking rate used in this experiment, direct fecal deposition in the pasture stream contributed more P than transport in precipitation runoff. The incidence of fecal pathogens E. coli O157:H7, bovine coronavirus, and bovine rotavirus shedding in the feces of the cows in this experiment as well as in the runoff from the rainfall simulations was extremely low. These results suggest that the major source of sediment and P loading of pasture streams is stream bank erosion primarily associated with stream hydrology. Grazing management practices that reduce congregation of grazing cattle near pasture streams will reduce sediment and nutrient loading resulting from direct fecal deposition or transport in precipitation runoff. While fecal pathogens may be potential pollutants of pasture streams, pathogen loading of pasture streams by grazing cattle is infrequent and dependent upon the pathogen shedding, temporal\spatial distribution of grazing cattle, and surface runoff from stream banks, in respective order.
Iowa State University
Schwarte, Kirk; Russell, James R.; Kovar, John; Morrical, Daniel G.; Ensley, Steve M.; Yoon, Kyoung-Jin; Cornick, Nancy; and Cho, Yong-Il
"Grazing Management Effects on Sediment, Phosphorus, and
Pathogen Loading of Pasture Streams,"
Animal Industry Report:
AS 657, ASL R2614.
Available at: https://lib.dr.iastate.edu/ans_air/vol657/iss1/38