oxisols

Oxisols are a soil order in tropical regions that form under very warm, humid conditions with long periods of intense rainfall. They develop through prolonged chemical weathering and heavy leaching, which remove many soluble bases and silicate minerals and leave a residual concentration of iron and aluminum oxides. Oxisols are widely distributed in the humid tropics, including the Amazon Basin, central Africa, and parts of Southeast Asia.

Key properties of oxisols include deep, strongly weathered profiles with limited horizon differentiation. They are typically well drained and very acidic, with low natural fertility due to their dominance of iron and aluminum oxides and low-activity clay minerals. Their cation exchange capacity is relatively low, so nutrients are easily lost from the soil or bound in forms that are not readily available to plants. The diagnostic feature is the oxic horizon, where Fe and Al oxides accumulate and less weatherable minerals are depleted, giving soils a characteristic reddish or yellowish color.

In soil classification, oxisols contrast with other tropical orders by their extreme degree of weathering and oxic horizon development. They are common under tropical rainforests and can persist for long periods of forest cover, but clearing or mismanagement can lead to erosion and rapid nutrient losses. Because of low inherent fertility, productive use typically requires substantial inputs of fertilizer and, in some cases, lime to mitigate acidity. Oxisols play a major role in tropical ecosystems and land-use planning, particularly where soils are heavily weathered and nutrient management is a consideration.