Based on different criteria soils may be clas­sified in different ways. Here a summary is being given of the bases for the classification of soils:

A. Parent Rocks-the physical properties of the soils very much depend on parent rocks. Hence, it is very good basis for the classification of soils. Based on this criterion the Indian soils may be classified into following 6 categories:

1. Soils formed by ancient crystalline and meta­morphosed rocks-this group includes red soils 1966 mainly formed by rocks like granites, gneiss, schist etc. and is rich in iron and manganese. Such soils are not very fertile.

2. Soils formed by rocks of Cuddaph and Vindhyan system-these are fully mature consisting of fine sandy and alkaline soils in the peninsular region.

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3. Soils formed by Gondwana rocks-these soils originating from the Gondwana rocks are not fully mature and hence are not very fertile. These depict thin layers with sandy and alkaline character­istics and dearth of humus.

4. Soils formed by Deccan Trap-this group includes regular or black soils of Maharashtra, Gujarat and Karnataka which are rich in iron and manganese and are well suited to the cultivation of cotton.

5. Soils formed by the Tertiary rocks-this category mainly includes Himalayan soils which are rich in lime and sand.

6. Soils formed by rocks of recent or Pleistocene period-this group includes alluvial soils of the Ganga plain which are fertile and yield good agricul­tural harvests.

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(B) Structure-based on this criterion soils may be classified under three main categories: (a) very loose, e.g. gravel, (b) loose, e.g. sand, and (c) compact, e.g. clay.

(C) Texture-based on the size of particles there are four main soil-types: (a) gravel (diameter of particles over 2 mm.), (b) sand (2.0 to 0.05 mm), (c) silt (0.05 to 0.002 mm), and (d) clay (less than 0.002 mm).

(D) Transporting Agency-this includes (a) collegial soils formed by the gravitational force and transported through avalanches, landslides, mudflows, slumps and creeps etc. Examples include talus or foot hill soils, (b) alluvial soils formed by the depositional activity of the rivers in the floodplains, deltaic plains and in the lagoons, (c) glacial soils consisting of moraines and till, (d) locustae soils, (e) eolian soils consisting of loess and windblown dust, and (f) dune soils consisting of quartz sand and desert soils.

(E) Organic Contents-(a) Mucus: organic contents 20 to 60%, and (b) Peat-organic contents more than 70%.

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(F) Climatic Reaction-(a) Forest soils-grey, brown and yellow; (b) Grassland soils-black, chest­nut, brown; and (c) Desert soils.

(G) Colour-(a) black, (b) red, (c) brown, (d) yellow, etc.

(H) Time-(a) mature soils, e.g. black soils, red soils etc. ; and (b) immature soils, e.g. desert soils, mountain soils, alluvial soils.

(I) Land Revenue-this is based on the fertil­ity and productivity of the soils. Thus we have (a) Goend or Gauhan, (b) Manjha or Har, and (c) Palo.

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(J) According to Marbut soils may be classified into two broad categories-(a) Peddlers: These are characterised by the existence of heavy minerals like iron and aluminum and are acidic in nature with less humus contents. Such soils develop in the moist areas of the Peninsula, e.g. red soils, (b) Pedicels develop in the semi-arid and arid regions of the north-western India where calcium is accumulated to the upper horizon through capillary action. These soils are non-acidic and rich in lime.