ABSTRACT
The view of soils as physical media whose purpose is to support plants, rather than as complex biophysical systems in their own right, still dominates the approaches to soil management in intensive cropping systems worldwide, and especially in the highly productive row-crop systems of temperate regions. Two generalizations illustrate characteristics of temperate-region soils that significantly differentiate them from tropical soils. Agricultural soils in temperate regions tend to be geologically young in comparison to large regions of the tropics. The inherent fertility of many temperate-region soils in mesic climates is high. Cultivation exposes soil aggregates to more frequent wet-dry and freeze-thaw cycles that break apart aggregates, especially the larger ones, thereby exposing trapped organic carbon to aerobic microbes that easily respire it as carbon dioxide. Most cropping systems use and export nutrients at prodigious rates.
