Nitisol

Nitisols form from fine-textured material weathered from intermediate to basic parent rock and kaolinite, halloysite and iron 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.

Related FAO soil groups originating in tropical climates and also containing layers with clay accumulations are Acrisols and Lixisols.