Soil Profile and Soil Types :

A number of soil types that cover extensive areas possess distinctive soil profiles. Podzols derive their name from the Russian words pod (“under”) and zola (“ash”), because of their strongly bleached E-horizon. This bleached horizon, the result of intense leaching, underlies a thick surface O-horizon, and overlies a brown B-horizon in which iron, aluminium, and, sometimes, humus have accumulated. Podzols are characteristic of cool environments with vegetation, such as conifers and heaths, that produces acid litter. Podzols are acidic with a low nutrient status, so cultivation is difficult. They are used mostly for forestry and grazing.

Chernozems (black earths) are characteristic of the great temperate grasslands of the world, with cold winters, hot summers, and an excess of evapotranspiration over precipitation. There is a rapid incorporation of organic matter into the soil accompanied by its humification, and by the leaching of soluble salts and carbonates. Some carbonates are redeposited in the middle of the soil. There is tremendous small-vertebrate and earthworm activity, which aerates and mixes the soil. Chernozems are extremely fertile because of their high nutrient status, good structure, and high water-holding capacity. They are used largely for the extensive cultivation of cereal crops. Brown Earths, typical of temperate deciduous woodland, possess a relatively thin surface O-horizon underlain by a light brown, weathered B-horizon. Other horizons are obliterated by the operation of soil organisms. A variety of red and reddish-brown soils occur in wet equatorial and tropical wet-dry climates, with rainforest and semi-deciduous tropical forests being the principal plant communities. Such soils are characterized by the intense weathering of bedrock into clays and contain a variety of oxides, including iron. On exposure such soils tend to harden and produce laterite. Because of their low nutrient status and low content of organic matter they are of low fertility. When the forest is cleared, what little fertility exists is soon lost.