Summary and Implications
To evaluate the effects of grazing management on pasture properties related to soil erosion and P pollution of streams, six 30-acre cool season grass pastures bisected by a stream were grazed by 15 fall-calving Angus cows by continuous stocking with full access to the stream, continuous stocking with stream access limited to a 16 x 80 foot stabilized crossing, or rotational stocking. The riparian paddocks of rotationally stocked pastures were never grazed to a sward height lower than 4 inches or longer than 4 days. Congregation areas in pastures had greater proportions of the ground that were bare or covered with manure and lower forage sward heights and masses than open areas. Stream banks had greater proportions of ground that was bare and lower forage sward height and masses than in the riparian zone from 110 to 220 feet from the bank and in the uplands. Pastures with continuous stocking and full stream access had greater proportions of bare soil and lower forage sward heights and masses on and adjacent to the stream bank compared to upland zones in the same pastures or on and adjacent to the stream bank in the ungrazed riparian buffers. This damage was particularly evident in October which would leave the banks susceptible to erosion during the winter. There was no difference in manure distribution across the different zones in pastures with full stream access. Pastures with continuous stocking and limited stream access had less bare soil, greater forage sward heights and masses on and adjacent to the banks than pastures with full stream access. There was no manure cover on or adjacent to the banks of riparian buffers in pastures with limited stream access, but manure cover was concentrated in the zone from 110 to 220 feet from the stream. The proportions of bare soil on and adjacent to stream banks in rotationally grazed pastures did not differ from ungrazed buffers and the forage sward heights and masses in these zones were intermediate between pastures with full and limited access in October. However, similar to pastures with continuous grazing and full access, manure coverage did not differ across zones of rotationally grazed pastures.
The preliminary results of this project imply that limiting access to streams to stabilized crossings or use of rotational grazing may decrease the potential for sediment and phosphorus loading from stream bank erosion.
Iowa State University
Russell, James R.; Kovar, John; Morrical, Daniel G.; Strohbehn, Daryl R.; Powers, Wendy J.; and Lawrence, John D.
"Effects of Grazing Management on Pasture Characteristics Affecting Sediment and Phosphorus Pollution of Pasture Streams (Progress Report),"
Animal Industry Report:
AS 652, ASL R2122.
Available at: http://lib.dr.iastate.edu/ans_air/vol652/iss1/45