Technical Abstract: The Soil Conditioning Index (SCI) has been proposed to predict the consequences of management actions on the state of soil organic carbon (SOC). The index was developed based on research in humid, temperate, loamy soils but has not been tested for many other conditions. In this project, we determine the effects of management on SOC in semiarid, thermic, sandy soils. Study sites were located in the Southern High Plains of west Texas (SHP) where long-term native range or grasslands were adjacent to cropland. Agroecosystems studied included native rangeland, conservation grassland, cotton, wheat, wheat-cotton rotations, high residue sorghum/forages, and a sunflowers wildlife planting. The cropland included irrigated and dryland, conventionally-tilled and no-tillage systems. Three replications were sampled on each field. Soil properties measured in the upper 10 cm were soil texture, bulk density, pH, phosphorus, nitrate and total nitrogen, total organic and particulate organic matter carbon, and wet aggregate stability. The SCI was determined using RUSLE2. Soil conditioning index values varied from -1.49 for conventionally-tilled dryland cotton to 2.29 for the conservation grassland. The SCI was negative for all conventionally tilled sites and positive for the native rangeland, conservation grassland and all no tillage sites with the exception of a low production, no tillage dryland wheat site. The SCI was most strongly correlated with the average residue production (r=0.67) as estimated in RUSLE2 and particulate organic matter (r=0.53). In this study, the OM sub-factor of SCI was not correlated with SOC mass but was correlated with particulate organic matter carbon (r=0.42; P<0.007) and was most strongly correlated with the average residue production (r=0.71; P<0.0001).