Soils of India: Factors of Soil Formation, Classification, distribution, and Characteristics

 Soil can be simply defined as a mixture of small rock particles/debris and organic materials/ humus which develop on the earth surface and support growth of plants.

 Soils are formed through the interaction of five major factors: time, climate, parent -material, topography and relief and organisms.

 The relative influence of each factor varies from place to place,  but the combination of all five factors normally determines the kind of soil developing in any given place.

factors contributing to soil formation in India

 The following are brief explanations of the factors contributing to soil formation in India.

1. Parent material: 

This refers to the mineral material, or organic material from which the soil is formed. 

Soils will carry the characteristics of its parent material such as color, texture, structure, mineral composition and so on. 

For example, if soils are formed from an area with large rocks (parent rocks) of red sandstone, the soils will also be red in color and have the same feel as its parent material.

2. Time: 

Soils can take many years to form. 

Younger soils have some characteristics from their parent material, but as they age, the addition of  organic matter, exposure to moisture and other environmental factors may change its features.

 With time, they settle and are buried deeper below the surface, taking time to transform. Eventually they may change from one soil type to another.

3. Climate: 

This is probably the most important factor that can shape the formation of soils. Two important climatic components, temperature and precipitation. 

They determine: how quickly weathering will be, what kind of organic materials may be available on and inside of the soils.

Moisture determines the chemical and biological reactions that will occur as the soils are formed.

 Warmer climate with more rainfall means more vegetative cover and more animal action. It also means more runoff, more percolation and more water erosion. 

They all help to determine the kind of soils in an area.

4. Relief: 

This refers to the landscape position and the slopes it has. Steep, long slopes mean water will run down faster and potentially erode the surfaces of slopes. 

The effect will be poor soils on the slopes, and richer deposits at the foot of the slopes.

 Also, slopes may be exposed to more direct sunlight, which may dry out soil moisture and render it less fertile.

5. Organisms: 

The source and richness of organic matter is down to the living things (plants and animals) that live on and in the soils.

 Plants in particular, provide lots of vegetative residue that are added to soils

 Their roots also hold the soils and protect them from wind and water erosion.

 They shelter the soils from the sun and other environmental conditions, helping the soils to retain the needed moisture for chemical and biological reactions.

 Fungi, bacteria, insects, earthworms, and burrowing animals help with soil aeration. Worms help breakdown organic matter and aid decomposition.

 Animal droppings, dead insects and animals result in more decaying organic matter.

 Microorganisms also help with mineral and nutrient cycling and chemical reactions.

Soil Defenition

Soil can be simply defined as a mixture of small rock particles/debris and organic materials/ humus which develop on the earth surface and support growth of plants.

Soil Classification – Urvara vs Usara

 In India, soil had been classified from the ancient period itself even though it was not as detail as the modern classifications.

 In the ancient period, the classification was based on only two things; whether the soil is fertile or sterile. Thus the classification were:

1. Urvara [fertile]

2. Usara [sterile]

Soil Classification – Agencies involved

 In the modern period, when men started to know about the various characteristics of soil they

began to classify soil on the basis of texture, colour, moisture etc.

 When the Soil survey of India was established in 1956, they studied soils of India and their

characteristics.

 The National Bureau of Soil Survey and the Land Use Planning, an institute under the control of Indian Council of Agriculture Research did a lot of studies on Indian soil.

Major classification of Indian soils

1. Alluvial soil [43%]

2. Red soil [18.6%]

3. Black / regur soil [15%]

4. Arid / desert soil

5. Laterite soil

6. Saline soil

7. Peaty / marshy soil

8. Forest soil

9. Sub-mountain soil

10. Snowfields

Alluvial soil:

 Mostly available soil in India (about 43%) which covers an area of 143 sq.km.

 Widespread in northern plains and river valleys.

 In peninsular-India, they are mostly found in deltas and estuaries.

 Humus, lime and organic matters are present.

 Highly fertile.

 Indus-Ganga-Brahmaputhra plain, Narmada-Tapi plain etc are examples.

 They are depositional soil – transported and deposited by rivers, streams etc.

 Sand content decreases from west to east of the country.

 New alluvium is termed as Khadar and old alluvium is termed as Bhangar.

 Colour: Light Grey to Ash Grey.

 Texture: Sandy to silty loam or clay.

 Rich in: potash

 Poor in: phosphorous.

 Wheat, rice, maize, sugarcane, pulses, oilseed etc are cultivated mainly.

Red soil:

 Seen mainly in low rainfall area.

 Also known as Omnibus group.

 Porous, friable structure.

 Absence of lime, kankar (impure calcium carbonate).

 Areas: peninsula from Tamil Nadu in the south to Bundelkhand in the north and Rajmahal

hills in the east to kachchh in the west (Tamil Nadu, Karnataka, Southern Maharashtra,

Chhattisgarh, Andra Pradesh, Orissa, jharkhand)

 Deficient in: lime, phosphate, manganese, nitrogen, humus and potash.

 Colour: Red because of Ferric oxide. The lower layer is reddish yellow or yellow.

 Texture: Sandy to clay and loamy.

 Wheat, cotton, pulses, tobacco, oilseeds, potato etc are cultivated.

Black soil / regur soil:

 Regur means cotton – best soil for cotton cultivation.

 Most of the Deccan is occupied by Black soil.

 Mature soil.

 High water retaining capacity.

 Swells and will become sticky when wet and shrink when dried.

 Self-ploughing is a characteristic of the black soil as it develops wide cracks when dried.

 Rich in: Iron, lime, calcium, potassium, aluminum and magnesium.

 Deficient in: Nitrogen, Phosphorous and organic matter.

 Colour: Deep black to light black.

 Texture: Clayey.

 Areas:developed by the weathering of the Deccan lava; Maharashtra, western Madhya

Pradesh, Gujarat, Andra Pradesh, Karnataka, Rajasthan, Tamil Nadu and Uttar Pradesh.

Laterite soil:

 Name from Latin word ‘Later’ which means Brick.

 Become so soft when wet and so hard when dried.

 In the areas of high temperature and high rainfall.

 Formed as a result of high leaching.

 Lime and silica will be leached away from the soil.

 Organic matters of the soil will be removed fast by the bacteria as it is high temperature and

humus will be taken quickly by the trees and other plants. Thus, humus content is low.

 Rich in: Iron and Aluminum

 Deficient in: Nitrogen, Potash, Potassium, Lime, Humus

 Colour: Red colour due to iron oxide.

 Rice, Ragi, Sugarcane and Cashew nuts are cultivated mainly.

 Areas: summits of Sahyadris, eastern ghats, Rajmahal hills, Satpuras, Vindhyas etc.

Desert / arid soil:

 Seen under Arid and Semi-Arid conditions.

 Deposited mainly by wind activities.

 High salt content.

 Lack of moisture and Humus.

 Kankar or Impure Calcium carbonate content is high which restricts the infiltration of water.

 Nitrogen is insufficient and Phosphate is normal.

 Texture: Sandy

 Colour: Red to Brown.

 Areas:Rajasthan, Saurashtra, Kachch, Haryana, south Punjab.

Peaty / marshy soil:

 Areas of heavy rainfall and high humidity.

 Growth of vegetation is very less.

 A large quantity of dead organic matter/humus which makes the soil alkaline.

 Heavy soil with black colour.

 Areas: Kottayam and Alappzha (Kerala), Orissa, West Bengal, Tamil Nadu, Bihar

Forest soil:

 Regions of high rainfall.

 Occur between 3000m-3100m in Himalayas

 Rich in plant nutrients, deficient in potash, phosphorus and lime

 Humus content is less and thus the soil is acidic.

 Areas: eastern ghats,tarai tract of U.P, Sahyadris

Mountain soil:

 In the mountain regions of the country at 2100m to 3000 m.

 Immature soil with low humus and acidic.

 Areas: Himalayas of Assam, Darjeeling, Uttarakhand, Himachal Pradesh, Kashmir.