Understanding of the Impacts of Grazing Sheep
March 15, 2013

A U.S. Department of Agriculture scientist is giving guidance to growers in Montana and the Dakotas on how grazing sheep when fields are left fallow will affect soil quality. 
Grazing sheep and other livestock was once common in the region before fertilizers were introduced in the 1950s. While fertilizers increased yields, they also increased nitrogen runoff and leaching, made soils more acidic and contributed to greenhouse gas emissions, according to Upendra Sainju, a soil scientist with the Agricultural Research Service in Sidney, Mont. 
The results of the study showed that tillage did return more of the beneficial wheat residue to the soil than either grazing or the herbicide treatments, resulting in higher levels of calcium, sulfur and electrical conductivity in the soil. 
But grazing generally had no negative effects on soil organic matter and crop yields. The sheep returned to the soil some of the phosphorus and potassium they ate up in the wheat residue by way of their feces and urine. Grazing also increased levels of magnesium and sodium in the soil, possibly because the urine and feces contained higher levels of them. 
The results of this study are available at www.ars.usda.gov/News/docs.htm?docid=1261.