Soil types correspond closely to their respective climatic and natural vegetation regions. In the permafrost region of northern Asia are tundra soils, unusable for agriculture because of the short growing season and impeded drainage but otherwise rich in organic matter. South of the tundra, in the vast coniferous forest region of cold temperate Asia, are podzols with high acidity and low organic content. Farther south, in the zone of mixed coniferous and deciduous forests, the gray brown forest soils have higher humus content and are less acidic than the podzols. Between the temperate forests of northern Asia and the deserts of Central Asia a belt of chernozem and chestnut soils appears. These black to dark-brown soils are very rich in humus and mineral nutrients and are very productive when farmed. The desert and mountain soils of dry Asia have little to offer for agricultural production. Even where irrigation is possible, a danger of salt and alkali accumulation in the topsoil exists resulting from the evaporation of mineralized underground water through capillary action. Consequently, cultivation in dry Asia is confined to well-drained alluvial soils along major river valleys.
The soils of hot, humid monsoon Asia belong to the major soil category known as pedalfers. These soils are rich in iron and aluminum material. High temperatures promote rapid oxidation and contribute to their reddish or yellowish appearance. Heavy rainfall washes soluble mineral and organic matter from the topsoil to the subsoil, leaving insoluble minerals, such as aluminum, in the topsoil. These tropical red earths are generally infertile, and therefore agriculture in monsoon Asia is confined mostly to alluvial soils along river valleys. Some prominent exceptions exist: soils developed on basic volcanic ash in the northeastern Deccan Plateau (India) and in Java are among the richest soils in monsoon Asia.