ACRISOL

one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Acrisols form on old landscapes that have an undulating topography and a humid tropical climate. Their natural vegetation is woodland, which in some areas has given way to tree savanna maintained by seasonal burning. The age, mineralogy, and extensive leaching of these soils have led to low levels of plant nutrients, excess aluminum, and high erodibility, all of which make agriculture problematic. Nevertheless, traditional shifting cultivation of acid-tolerant crops has adapted well to the conditions found in Acrisols. They occupy just under 8 percent of the continental land surface on Earth, covering areas throughout central and northern Latin America, Southeast Asia, and West Africa. Acrisols are defined by the presence of a subsurface layer of accumulated kaolinitic clays where less than half of the ions available to plants are calcium, magnesium, sodium, or potassium and also by the lack of an extensively leached layer below the surface horizon (uppermost layer). They are related taxonomically to the Oxisol soil order of the U.S. Soil Taxonomy. Related FAO soil groups originating in tropical climates and also containing layers with clay accumulations are Lixisols and Nitisols.