Yakovchenko, V., Sikora, L., and D. Kaufman. 1996. A biologically based indicator of soil quality. Biology and Fertility of Soils 21:245-251.

Abstract: Soil quality indices are attempts to classify soil conditions and to compare these conditions to their historical use. From this information it may be possible to determine which uses of soils are better for the long-range goals of agriculture and society. With many factors involved in the profitable production of safe foodstuffs without significant degradation of the environment and soils, an indicator that represents a broad biological perspective of quality is appropriate. Among a group of biological indicators, the ratio of crop N uptake to mineralized N as determined by microbial respiration plus net mineralized N found over a growing season is a useful indicator of soil quality. An evaluation of the 12-year-old Farming Systems Trial at the Rodale Institute Research Center indicated that soils in plots that had been conventionally managed were of lower quality than soil treated with manure or planted with legume-cash grain crops.