Soils: Formation, Types, Erosion and Conservation

Understanding soil is crucial for agriculture and environmental sustainability. Soil, a mixture of rock debris and organic materials, forms layers known as horizons, each with distinct properties. Factors like parent material, climate, topography, biological activity, and time influence soil formation. Various types of soils, like alluvial, black, red and yellow, laterite, arid, saline, peaty, and forest soils, have unique characteristics and are found in different regions of India.

An Overview Of Soils:

• Soil Composition: Soil is a mixture of rock debris and organic materials that develop on the earth’s surface. Different particles present in the soil is as given below
  • Gravel: Particles greater than 2 mm in diameter.
  • Coarse sand: Particles less than 2 mm and greater than 0.2 mm in diameter.
  • Fine sand: Particles between 0.2 mm and 0.02 mm in diameter.
  • Silt: Particles between 0.02 mm and 0.002 mm in diameter.
  • Clay: Particles less than 0.002 mm in diameter.
• Soil Horizon: The arrangement of layers of soil is known as the soil profile. Different layers in the soil profile are called Horizons.
  • Horizon O: Surface litter and partially decomposed organic matter.
  • Horizon A: Topmost zone where organic materials have got incorporated with the mineral matter; includes humus, living creatures and inorganic minerals.
  • Horizon E: Eluviated Horizon, zone of leaching, this layer is no always present in the soil.
  • Horizon B: Iron, Aluminium and Humic compounds are accumulated and clay leached down from A and E horizon; zone of illuviation (accumulation); transition zone between the ‘horizon A’ and ‘horizon C’,
  • Horizon C: Composed of the loose parent material.  This layer is the first stage in the soil formation process

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Soil Forming Factors

• Parent Material: It is a passive factor in soil formation, encompassing in-situ weathered rock debris (residual soils) or transported deposits (transported soils).
• Topography: another passive factor, influences soil formation through sunlight exposure and drainage. 
  • On gentler slopes, soil formation is quite favourable.
• Climate: is an important active factor; Precipitation provides soil moisture vital for chemical and biological activities; 
  • Dry climates with high temperatures cause evaporation to exceed precipitation, leading to salt deposits called hardpans; 
  • Chemical activity is increased in higher temperatures, reduced in cooler temperatures (with an exception of carbonation) and stops in freezing conditions; 
  • tropical soils with higher temperatures show deeper profiles.
• Biological Activity: Active factor;  Vegetative cover and organisms act on parent materials; Bacterial activity etc.
• Time: Passive factor; mature soils result from extended operation of soil-forming processes.

Classification of Soils

• Historically, the soil was initially categorised simply as fertile (Urvara) or sterile (Usara). 
• In India, the major classification of soil has been outlined in the table below.

Soil Erosion

• Definition: Soil erosion, described as the destruction of soil cover, results from an imbalance between soil-forming and erosional processes, intensified by natural or human factors.
• Types of Soil erosion
• • Splash Erosion: First stage of erosion process that occurs when raindrops hit bare soil;
  • Sheet Erosion: Uniform removal of a thin layer of finer and fertile top soil on level lands devoid of vegetative cover after a heavy shower and soil removal is not easily noticeable; 
  • Rill Erosion: occurs when sheet flows begin to concentrate on the land surface; leaves visible scouring on the landscape; 
  • Gully Erosion: Rill erosion evolves into gully erosion. Gullies resemble small valleys and are common on steep slopes. 
    • Gullies deepen with rainfall, cutting agricultural lands into small fragments and making them unfit for cultivation. 
    • A region with a large number of deep gullies or ravines is called a badland topography. 
    • Ravines are prominent in the Chambal basin and are also found in Tamil Nadu and West Bengal.

Soil Conservation

• Mulching: The bare ground between plants is covered with a layer of organic matter like straw. It helps to retain soil moisture.
• Contour Bunds/Barriers: Stones, grass, soil are used to build barriers along contours. Trenches are made in front of the barriers to collect water.
• Rock Dam: Rocks are piled up to slow down the flow of water. This prevents gullies and further soil loss.
• Terrace Farming: Broad flat steps or terraces are made on steep slopes so that flat surfaces are available to grow crops and surface runoff and soil erosion could be reduced.  
  • Examples: Western and central Himalayas have well-developed terrace farming.
• Intercropping: Different crops are grown in alternate rows and are sown at different times to protect the soil from rain wash.
• Contour Ploughing:  Ploughing parallel to the contours of a hill slope to form a natural barrier for water to flow down the slope.
• Strip Cropping: Large fields can be divided into strips. Strips of grass are left to grow between the crops. This breaks up the force of the wind. This method is known as strip cropping. 
• Shelterbelts: Planting lines of trees to create shelter are called shelter belts; used for stabilizing the desert in western India.

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Conclusion

• Understanding soil is important for farming and protecting the environment. Soil erosion, caused by natural processes or human activities, poses a significant threat to agriculture and the environment. 
• Soil conservation methods are essential for preserving fertile land and preventing erosion. 
• Through techniques like mulching, contour bunds, and terrace farming, we can protect soil from degradation and ensure sustainable agriculture. 
• By appreciating the significance of soil and implementing conservation practices, we can safeguard our environment for future generations.

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