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 rangelan d resources. Pastures at the High Plains Grasslands Research Station n ear Cheyenne, Wyoming grazed for the past II years at a heavy stocking rate (67 steer-days/ha) under three light grazing (22 steer-days/ha) and to livestock exclosures. The heavy stocking rate resulted in sligh tly less than 50% utilization of the annual forage produced a level re commended by land management agencies. Prior to initiating this grazin g 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 mt (36 in) depth. Soils had higher amounts of carbon an d nitrogen in the surface 30 cm (12 in) on the grazed pastures compare d to native rangeland where livestock were excluded. However, soil car bon and nitrogen below 30 mt was similar among all grazing treatments. Carbon and nitrogen dynamics were greatest in the surface 30 mt where more than three-fourths of the plant root biomass exists. Grazing str ategies and stocking rates imposed for the past II years on this mixed grass prairie did not detrimentally affect soil organic carbon and ni trogen levels. The data in fact, suggest that responsible grazing enha nced the overall soil quality as assessed by these parameters.