Alisol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Alisols are highly acidic, poorly drained soils prone to aluminum toxicity and water erosion. Liming and fertilization are essential to their agricultural use—primarily for growing oil palm, corn (maize), and cotton. Their extent has not been established definitively, but they are believed to occupy less than 1 percent of the total land area on Earth, predominately in the southeastern United States (in soil zones currently classified as Acrisols) and Malaysia.
Alisols are characterized by the presence of a dense subsurface layer of accumulated clay of mixed mineralogy (mostly kaolinitic) containing a significant amount of readily soluble aluminum ions bound to soil particles and by the lack of an extensively leached layer below the surface horizon (uppermost layer). They occur under the same topographic conditions as Acrisols but in climates with greater precipitation and higher temperatures. Alisols are also related to the Lixisol and Nitisol groups in the FAO classification system and to the Ultisol order of the U.S. Soil Taxonomy.