Oxisols

Oxisols (from French oxide, "oxide") are very highly weathered soils that are found primarily in the intertropical regions of the world. These soils contain few weatherable minerals and are often rich in Fe and Al oxide minerals. Most of these soils are characterized by extremely low native fertility, resulting from very low nutrient reserves, high phosphorus retention by oxide minerals and low cation exchange capacity (CEC). Most nutrients in Oxisol ecosystems are contained in the standing vegetation and decomposing plant material. Despite low fertility, Oxisols can be quite productive with inputs of lime and fertilizers. The Oxisols are divided into five suborders: Aquox, Torrox, Ustox, Perox and Udox.

Oxisols occupy approximately 7.5% of the global ice-free land area. In the U.S., they only occupy approximately .02% of the land area and are restricted to Hawaii.

Oxisols layers of soil
Oxisols have either: (1) an oxic horizon (low CEC, less than 10% weatherable mineral content); or (2) at least 40% clay between the mineral soil surface and 18 cm and a kandic horizon that meets the weatherable mineral requirement of an oxic horizon. (USDA-NRCS)

Oxisols (Brazil)

Oxisols are the dominant soil order in Brazil, covering over 40% of the country's territory

Torrox (Hawaii)

Oxisols of arid climates

Perox (Hawaii)

Oxisols of continuously humid climates, where precipitation exceeds evapotranspiration in all months

Plinthite

Plinthite is an iron-rich, humus-poor mixture of clay with quartz and other minerals

Oxisols and agriculture

A significant but challenging soil type for agriculture due to their low fertility, low cation exchange capacity and tendency to fix phosphorus