Adaptation of soil quality indices and application to three tillage systems in southern Illinois

Sustainability of agricultural management systems has become an issue of wi de public concern and international debate. One result is that soil quality assessment has been suggested as a tool for evaluating sustainability of s oil and crop management practices. Our objective was to adapt a soil qualit y index to assess the effects of three long-term tillage systems on sloping Grantsburg silt loam soil. Soil quality was evaluated using a framework th at included three soil functions: (1) resist erosion (water relations), (2) provide plant nutrients (nutrient relations), and (3) provide a favorable root environment (rooting relations). A score for each of these functions w as computed using measurements (indicators) that were normalized with one o f the three (more is better, optimum, or worse) scoring functions. Six diff erent indices were developed from a basic framework. Modifications included changing the weighting factors, threshold limits, or type of scoring funct ion applied to indicators, and the addition of air-filled and water storage porosity to the nutrient and rooting relations functions. Changing thresho ld limits and the type of scoring function used for surface residue improve d the correlation between water relations and soil lass. The addition of po rosity indicators increased the sensitivity of nutrient and rooting relatio ns functions to yield and cone index, respectively, and resulted in a bette r correlation between porosity indicators and plant population. Computing s oil quality indices helped to combine different soil properties and process es into a simple tool that explained changes in complex soil properties in response to different tillage practices. This supports previous studies sug gesting that computing soil quality indices and functions could be useful f or selecting management practices to maintain or improve soil quality. Our results demonstrated that adjusting threshold limits for local conditions c an make the function ratings more or less sensitive to thr management pract ices being evaluated. (C) 1999 Elsevier Science B.V. All rights reserved.