In the context of agricultural problem soils, acid soils are soils in which acidity dominates the problems related to agricultural land use. However, the Reference Soil Groups with the widest distribution of acid soils are Acrisols, Ferralsols and Podzols.
Acid soils occur in the tropics and subtropics as well as in moderate climates.
Their formation depends on specific conditions of climate, topography, vegetation, parent material and time for soil formation. Acrisols and Ferralsols are most common in old land surfaces in humid tropical climates. Acid sulphate soils occur in the tropics, in low-lying coastal land formerly occupied by mangrove swamps. Podzols are typical soils of the northern coniferous forests but may occur in the tropics, too. The types of acid soils vary considerably due to different factors in soil formation, especially differences in climate, parent material and vegetation.