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ARS Home » Plains Area » Lubbock, Texas » Cropping Systems Research Laboratory » Wind Erosion and Water Conservation Research » Research » Publications at this Location » Publication #206460
Title: Investigation of Soil Conditioning Index Values for Southern High Plains Agroecosystems

Author
item Zobeck, Teddy
item CROWNOVER, JAMES - USDA-NRCS (RETIRED)
item DOLLAR, MONTY - USDA-NRCS
item Van Pelt, Robert - Scott
item Acosta-Martinez, Veronica
item BRONSON, KEVIN - TEXAS A&M
item Upchurch, Dan

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2007
Publication Date: 11/1/2007
Citation: Zobeck, T.M., Crownover, J., Dollar, M., Van Pelt, R.S., Acosta Martinez, V., Bronson, K.F., Upchurch, D.R. 2007. Investigation of soil conditioning index values for Southern High Plains agroecosystems. Journal of Soil and Water Conservation. 62(6):433-442.

Interpretive Summary: The United States Department of Agriculture, Natural Resources Conservation Service (USDA-NRCS) has proposed the Soil Conditioning Index (SCI) to predict the consequences of management actions on the state of soil organic matter, a soil quality indicator. The SCI predicts changes in soil organic matter by considering plant material produced and returned to the soil, the influence of climate on organic matter decay, and the influence of field operations and erosion. 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 soil organic matter and the SCI in semiarid, hot, sandy soils. Study sites were located in the Southern High Plains of western Texas where long-term native rangelands or grasslands were near to cropland. This study included native rangeland, conservation grassland, various cotton and wheat rotations, and a high-residue forage sorghum. The sites included irrigated and dryland conditions under conventionally tilled and no-tillage farming systems. All native rangelands and conservation grasslands and no-tillage fields (dryland and irrigated) had positive SCI values, which indicates increasing organic matter levels. In contrast, all of the conventionally-tilled cotton fields had negative SCI values, indicating decreasing organic matter levels. Fields with a wheat cover crop that was chemically killed before cotton planting had positive and negative SCI values depending upon tillage intensity. The SCI was most strongly related to the residue left on the field and a specific type of organic matter. The SCI successfully distinguished fields with the highest levels of organic matter and when no-tillage or limited tillage management was practiced from fields that were more aggressively tilled.

Technical Abstract: The United States Department of Agriculture, Natural Resources Conservation Service (USDA-NRCS) has proposed the Soil Conditioning Index (SCI) to predict the consequences of management actions on the state of soil organic carbon (SOC), a soil quality indicator. The SCI predicts qualitative changes in soil organic matter by considering biomass produced and returned to the soil, the influence of climate on organic matter decay, and the influence of field operations and erosion. 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 western Texas (SHP) where long-term native rangelands or grasslands were adjacent to cropland. Agroecosystems studied included native rangeland, conservation grassland, cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum, L.) rotations, and a high-residue forage sorghum (Sorghum bicolor, L.). The sites included irrigated and dryland conditions under conventionally tilled and no-tillage practices. 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 (POM-C), and wet aggregate stability. The SCI was determined using RUSLE2. Mean SCI values varied from -1.49 for conventionally-tilled dryland cotton to 2.15 for the conservation grassland. All native rangelands and conservation grasslands and no-tillage fields (dryland and irrigated) had positive SCI values, which indicates increasing organic matter levels. In contrast, all of the conventionally-tilled cotton fields had negative SCI values, indicating decreasing organic matter levels. Fields with a wheat cover crop that was subsequently chemically killed before cotton planting had positive and negative SCI values depending upon tillage intensity. The SCI was most strongly correlated with the residue equivalent value (r=0.68) as estimated in RUSLE2, but based on measured values, and particulate organic matter carbon (r=0.57). The SCI successfully distinguished fields with the highest levels of SOC and when no-tillage or limited management was practiced from agroecosystems that were aggressively tilled. Additional research is needed to adjust the SCI sub-factors to better relate the index with SOC.