|Van Pelt, Robert - Scott|
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 6/2/2006
Publication Date: 6/26/2006
Citation: Zobeck, T.M., Crownover, J., Dollar, M., Van Pelt, R.S., Acosta Martinez, V., Bronson, K.E., Upchurch, D.R. 2006. Southern high plains conservation systems effects on the soil conditioning index and other soil quality indexes[abstract]. 28th Southern Conservation Systems Conference, June 26-28, 2006, Bushland, Texas. p. 269.
Interpretive Summary: The Soil Conditioning Index (SCI) has been proposed by the USDA, Natural Resource Conservation Service as a method to predict the effects of various land management practices on soil organic matter. However, this index was developed using data from humid, temperate areas on loamy soils and has not been tested in sandy soils in hot dry regions of the US. We studied a wide variety of land management systems including various cropping systems, and managed and native grasslands on the Southern High Plains of west Texas. Irrigated and dryland, conventional and no-tillage systems were studied. Values less than zero indicate organic matter is being depleted and values greater than zero indicate organic matter is being conserved. The SCI is determined by considering the effects of tillage intensity, organic matter returned to the soil, and wind and water erosion. All conventionally-tilled systems had a negative SCI value while the grasslands and most no-tillage sites had positive SCI values. Among the no-tillage systems, only a very low productivity dryland wheat site had a slightly negative SCI value. Although the stated purpose of the SCI is to predict the consequences of management actions on the state of soil organic matter, the SCI values were not strongly correlated with total soil organic matter. The SCI values were strongly related with the average residue produced on the site and a certain form of poorly decomposed organic matter called particulate organic matter. The SCI has value as a tool to predict the effects of management on some soil quality indicators related to crop production. However, caution is recommended for interpreting values estimated close to zero.
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).