Nitisol, in theWorld Reference Base for Soil Resources (WRB), is a deep, red, well-drainedsoil with aclay content of at least 30% and a polyhedralstructure or a blocky structure, breaking into a polyhedral or a flat-edged structure. The soil aggregates show pressure faces. Nitisols correlate with thekandicalfisols,ultisols andinceptisols of theUSDA soil taxonomy.[1][2]
These soils are found in the tropics and subtropics; there are extensive areas of them in the tropical highlands ofEthiopia,Kenya,Democratic Republic of the Congo andCameroon. Nitisols form from fine-textured material weathered from intermediate tobasic parent rock andkaolinite,halloysite andiron oxides dominate their clay mineralogy.
Nitisols are technically defined by a significant accumulation of clay (30 percent or more by mass and extending as much as 150 cm [5 feet] below the surface) and by a blocky aggregate structure. Iron oxides and high-water content are believed to play important roles in creating the soil structure. Nitisols are also strongly influenced by biological activity, resulting in a homogenization of the upper portion of the soil profile. These soils are related to theAlfisol andInceptisol orders of theU.S. Soil Taxonomy. RelatedFAO soil groups originating in tropical climates and also containing layers with clay accumulations areAcrisols andLixisols.[3]
