5.4. Soil Classification

Soil is not found same everywhere. A soil of one place is different from that of the other. Early classifications followed biological principles to group soils. One of the most important classifications of soils has been the zonal system. This was proposed by Russian pedologists who recognized the strong relationship between climate, vegetation and soil zones throughout the world. Three main classes of soil are recognized.

Zonal soils are those that are well developed and reflect the influence of climate as the major soil-forming factor. They can be subdivided into podzol soils, Tundra soils, brown earth, Ferralsol, Chernozem, Chestnut and Prairie soils. Sierozem of desertic and semi-desertic areas is extreme form of chestnut.

Intrazonal types are well-developed soils formed where some local factor such as parent material, terrain or age is dominant. They can be subdivided into Calcimorphic soil(on calcareous parent material), Halomorphic soils(saline), and Hydromorphic soil (marshes, swamps or poorly drained upland).

Azonal soils are those that are immature or poorly developed. It lacks a B-horizon. Thus, A- horizon likes immediately above the C-horizon of weathered parent material. This may happened because of characteristics of parent material or nature of terrain or simply the lack of time for development. It is commonplace on active flood plains, volcanic soils, newly deposited glacial drift, windblown sand, marine mud-flats. Azonal soils are subdivided into Lithosol (erosion removes soil almost as fast as it is formed on steep slopes), Regosol (dry and loose dune sands) and alluvial soils(regular supply of sediments).