Rangeland soil carbon and nitrogen responses to grazing

Land managers, livestock producers, and the public are concerned about the effects of grazing on soil quality and sustainability of rangeland resources. Pastures at the High Plains Grasslands Research Station near Cheyenne, Wyoming, grazed for the past 11 years at a heavy stocking rate (67 steer-dayslha) under three management systems, were compared to continuous light grazing (22 steer-dayslha) and to livestock exclosures. The heavy stocking rate resulted in slightly less than 50% utilization of the annual forage produced, a level recommended by land management agencies. Prior to initiating this grazing research the rangeland had not been grazed for about 40 years. Soil organic carbon and nitrogen response were evaluated by collecting soil samples to 91 cm (36 in) depth. Soils had higher amounts of carbon and nitrogen in the surface 30 cm (12 in) on the grazed pastures compared to native rangeland where livestock were excluded. However, soil carbon and nitrogen below 30 cm was similar among all grazing treatments. Carbon and nitrogen dynamics were greatest in the surface 30 cm where more than three-fourths of the plant root biomass exists. Grazing strategies and stocking rates imposed for the past 11 years on this mixed grass prairie did not detrimentally affect soil organic carbon and nitrogen levels. The data, in fact, suggest that responsible grazing enhanced the overall soil quality as assessed by these parameters.