| Soil quality indices will be most useful if they are sensitive to management-induced changes, easily measured, inexpensive, and linked to desired values such as productivity. This study determined soil quality indicators in sod and cultivated plots that should be included in soil quality evaluation, and quantified the sensitivity of soil chemical, physical, and biological attributes to management change. Cultivation was detrimental to most properties: active and total soil organic matter declined; fewer culturable bacteria and fungi and lower microbial functional diversity occured; soil structure degraded, as shown by decreased aggregate size and vane shear strength, and by increased bulk density; microbial activities including arylsulfatase and β-glucosidase activity, denitrification potential, and denitrification enzyme activity declined. Only nitrification potential increased in cultivated plots. Sod and cultivated plots were converted to no-till maize, with and without manure, to evaluate the sensitivity of soil quality indicators to short-term transitional effects. Based on the direction and magnitude of change in soil quality indicators, soil degraded in plots where sod was converted to no-till maize, but the degradation was retarded by manure. Soil quality improved in converted cultivated plots only when manure was applied. Regression analysis was used to quantify the sensitivity of soil quality indicators by their initial rate of change and the time required for individual properties to reach 50% of minimum or maximum limits. Active soil organic matter and most soil biological properties were more sensitive than total organic matter and other soil chemical and physical properties. Aggregate size and vane shear strength were the most sensitive soil chemical and physical properties. The sensitivity of aggregate size to soil management was associated with the sensitivity of biologically active organic matter. There was a close relationship between soil aggregate size and biologically active C. Most of the soil properties sensitive to soil management were also sensitive to environment. Microbial diversity, arylsulfatase activity, and mineralizable N, were sensitive to management but only moderately sensitive to environment. The results suggest that some soil biological properties, aggregate size, and vane shear strength can serve as early signals of soil quality degradation or improvement. |
