An ordering of soil types. The simplest arrangement distinguishes between pedocals, rich in calcium carbonate, and pedalfers, low in calcium but high in compounds of aluminium and iron. The Great Soil Groups are zonal, azonal, and intrazonal. Of the zonal soils, podzols are found beneath coniferous forest, and latosols develop in warm, moist conditions. Chernozems, prairie soils, and chestnut soils are formed beneath grassland. Grey and red desert soils occur in hot, arid areas, and tundra soils form in periglacial environments.

Intrazonal soils include peats, saline solonchaks, and alkaline solonetz. Azonal soils include alluvium and sands. See also US soil classification.

A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved.