ABSTRACT
US Soil Taxonomy classified all soils into 10 orders. More recently, Andisols have been added to the classification scheme. The Aridisols make up the largest group of soils in semiarid regions. Aridisols, the most prevalent of all soil orders, occur mostly in hot, dry regions and are generally low in organic matter. The conversion of forest and grass lands into cropland is generally associated with a sharp decline in the content of soil organic matter. Johnson reviewed the effects of forest management on soil carbon storage. Carbon losses were strongly dependent on management regime and regional location. Burke concluded that the extent of soil organic matter depletion was dependent on same variables as those controlling soil organic matter formation: climate, soil texture, and landscape position. Hornick and Parr reported that, for most agricultural soils, degradative processes and conservation practices occur simultaneously. In semiarid regions, the dominant degradative processes are loss of soil organic matter and erosion by wind and water.
