Soil depletion is the loss of soil fertility through a decline in organic matter content, major mineral nutrients, and trace elements. Lowered levels of nutrients lead to poor crops and deficiencies in the diet of grazing animals and, thus, eventually in the human food chain. It is a major handicap in developing sustainable agriculture. The loss of nutrients is the result of both natural and anthropogenic processes. Soils more than 200,000 yrs. (years) old on rocks poor in base elements are particularly prone to nutrient and trace element depletion. In the southeastern United States, in forest soils up to 2 million yrs. old on base-poor igneous and metamorphic rocks, calcium (Ca) in [Page 2583]the rooting zone has been leached out of the soil profile. This ...