Effects of Livestock Grazing on Sediment Production, Edwards Plateau of Texas

Abstract

The influence of short duration grazing (SDG), moderate continuous grazing (MCG), heavy continuous grazing (HCG), and grazing exclusion on sediment production of midgrass and shortgrass-dominated communities was evaluated over a 20-month period on the Texas Agricultural Research Station located near Sonora in the Edwards Plateau, Texas. A combination of cattle, sheep, and goats was used in each grazing treatment. Sediment production was consistently less from the midgrass (bunchgrass) than from the shortgrass (sodgrass) community. The HCG pasture was severely overgrazed and resulted in excessive soil loss. The midgrasses in this pasture were destroyed after 26 months of overgrazing. Sediment production from the SDG pasture stocked at double the recommended rate increased during the study period. The SDG pasture, by the end of the study, had lost more sediment from both the midgrassand shortgrass-dominated communities than the MCG pasture. Sediment loss from the midgrass community in the MCG pasture was consistently low during the study; however, sediment production from the shortgrass community decreased in the MCG pasture. Sediment production from the midgrass community in the non-grazed pasture remained consistently low throughout the study, but the shortgrass community showed a strong decrease in sediment loss during the study. Historically, grazing has been an integral part of rangelands (Mack and Thompson 1982) and native herbivores have coevolved with grasslands and most shrublands. However, the introduction of domestic livestock increased the potential for adversely impacting rangeland watersheds. Rangelands by their very nature are naturally large contributors of sediment (Branson et al. 1981). Livestock grazing has the potential of altering the amount and kind of vegetation, which in turn potentially alters surface soil hydrologic characteristics (Blackburn et al. 1982). Reductions in the amount of vegetation may increase raindrop impact, decrease soil organic matter and aggregates, increase surface soil crusting, and decrease infiltration rates (Chapman 1933, Branson and Owen 1970, Blackburn 1975, Wood and Blackburn 1981). Altering the kind of vegetation may also increase sediment losses. Sediment production of sagebrush (Artemisia spp.) canopy zones in Nevada was less than that of the adjacent interspace areas (Blackburn 1975). Sediment loss from shortgrass-dominated sites in the Rolling Plains of Texas was greater than from adjacent midgrass or shrub canopy sites. Livestock grazing altered the sediment loss most from the midgrass-dominated areas and had little or no influence on the shrub canopy zones or shortgrass areas (Wood and Blackburn . 1982). Much interest has been generated by specialized grazing systems and their potentials for decreasing erosion and adding economic benefits to the ranching industry. However, little information is available to support many of the claims concerning specialized grazing systems (Gifford and Hawkins 1978, Blackburn et al. 1982). The purpose of this study was to determine: (1) the influence Authors are graduate research assistant, and professor of watershed management, Range Science Department, Texas AM and professor of range science, Texas Agricultural Experiment Station, Sonora 76950. Published with approval of the Director, Texas Agricultural Experiment Station, as TA1 8839. Manuscript received July 25, 1983. of heavy continuous grazing, moderate continuous grazing, short duration grazing, and no grazing on sediment loss, and (2) the variables influencing sediment loss.