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2007 Soil and Water Conservation Society - Soil Quality Workshop

"Soil Quality: the Foundation for Natural Resource Quality"


Ted M. Zobeck
USDA-ARS, Lubbock, TX

The United States Department of Agriculture, Natural Resources Conservation Service 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 was initially conceived in the 1970s based on long-term studies conducted in Renner, Texas. The index has been developed and improved and is now embedded in RUSLE2 and used for a variety of programs and inventories. However, the SCI was generally developed based on research in humid, temperate, loamy soils and questions have been raised concerning its use in semiarid regions and with sandy soils. A study of the use of SCI in west Texas was conducted to evaluate this concern. In this project, we determined the effects of management on SCI, SOC, and other soil properties in semiarid, hot, sandy soils located in the Southern High Plains of western Texas. Agroecosystems studied included native rangeland, conservation grassland, cotton and wheat rotations, and high-residue forage sorghum. The sites included irrigated and dryland conditions under conventionally tilled and no-tillage practices. 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. The SCI was most strongly correlated with the residue equivalent value (r=0.68) as estimated in the Revised Universal Soil Loss Equation, but based on measured values, and particulate organic matter carbon, POM-C (r=0.57). The SCI successfully distinguished fields with the highest levels of POM-C and when no-tillage or limited management was practiced from agroecosystems that were aggressively tilled.

Ted Zobeck - Dr. Zobeck is a Lead Scientist in the USDA Agricultural Research Service, Wind Erosion and Water Conservation Research Unit of the Cropping Systems Research Laboratory at Lubbock, Texas. Ted has worked as a Research Soil Scientist specializing in soil and water management and conservation for over 30 years and currently leads a five year project titled Soil Management for Sustainable Agricultural Systems that Prevent Wind Erosion and Enhance the Environment. He is an ARCPACS Certified Soil Scientist, a Licensed Professional Geoscientist and has authored or co-authored over 115 publications, including co-editing the proceedings of four meetings and numerous book chapters. He is past president of the Permian Basin Chapter and Golden Spread Chapter of the Soil and Water Conservation Society and is currently the Southwest Regional Representative on the SWCS Professional Development Committee. Dr. Zobeck is particularly interested in the effects of cropping systems on soil quality indexes and is currently working on projects evaluating the Soil Conditioning Index and comparing the SCI with the Soil Management Assessment Framework.