LIXISOL

one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Lixisols develop on old landscapes in a tropical climate with a pronounced dry season. Their age and mineralogy have led to low levels of plant nutrients and a high erodibility, making agriculture possible only with frequent fertilizer applications, minimum tillage, and careful erosion control. Perennial crops are thus more suitable for these soils than root or tuber crops. They occupy just under 3.5 percent of the continental land area on Earth, mainly in east-central Brazil, India, and West Africa. Lixisols are defined by the presence of a subsurface layer of accumulated kaolinitic clays, where at least half of the readily displaceable ions are calcium, magnesium, sodium, or potassium, but they are also identified by the absence of an extensively leached layer below the surface horizon (uppermost layer). They are related to the Oxisol order of the U.S. Soil Taxonomy. Related FAO soil groups originating in tropical climates and also containing layers with clay accumulations are Acrisols and Nitisols.