HOW SOIL IS FORMED

Orgin Of Soil

Soil are formed by weathering of rocks due to mechanical disintegration or chemical decomposition.When a rock get exposed to atmosphere over a significant time,it decomposes into small particles and these particle are formed as soil.

FORMATION OF SOIL:

• Physical Disintegration 
• Chemical Decomposition of rock

PHYSICAL DISINTEGRATION

1.Temperature Change: Different minerals of rock have different coefficients of thermal expansion.Temperature fluctuations cause expansion and contraction of the rock due to these changes stresses induced and the particles get detached from the rock and the soil are formed.

2.Wedging action of Ice: When water present in minute pores and cracks of rocks, during cold climates these water gets frozen.If the volume of ice formed is more than of water expansion occurs.

Rock get broken into pieces when large stresses develop in the cracks due to wedging action of the ice formed.

3.Spreading of roots of plants: As the roots of tree grow in the cracks and hole of the rocks,force acts on the rock.The segments of the rock are forced apart and disintegration of rocks occurs.

4.Abrasion: As water,wind and glaciers move over the surface of rock,abrasion and scouring takes place.It results in the formation of soil.

CHEMICAL DECOMPOSITION

1.  Hydration: Hydration is the inclusion of water in a mineral structure,causing it to swell and leaving it stressed and easily decomposed.

2.  Carbonation: It is a type of chemical decomposition in which carbon dioxide in the atmosphere combines with water to form carbonic acid.The carbonic acid react chemically with rocks and causes their decomposition.

3.  Oxidation: Oxidation occurs when oxygen ions combine with minerals of rocks.Oxidation results in decomposition of rocks.Oxidation of rocks is somewhat similar to rusting of steel.

 

4.  Solution: Some of the rock minerals from a solution with water when they get dissolved in water and soil are formed.

5.  Hydrolysis: It is a chemical process in which water gets dissociated into H+ and OH- ions.The hydrogen cation replace the metallic ions such as calcium,sodium and potassium in rock minerals and soils are formed with a new chemical decomposition.

TRANSPORTATION OF SOIL

• Water transported soil
• Wind transported soil
• Glacier-Deposited soil
• Gravity-Deposited soil
• Soil transported by combined action

MAJOR SOIL DEPOSITS OF INDIA

1. Alluvial Deposite: A large part of north India is covered by alluvial deposits.The characterstics of alluvial deposits is the existence of alternate layers of sand,silt and clay.

2. Black Cotton Soils: A large part of central India and a portion of South India is covered with black cotton soil.These soils are residual deposits formed from basalt or trap rocks.

3. Lateritic Soil: Lateritic soils are formed by decomposition of rock,removal of bases and silica and accumulation of iron oxide and aluminium oxide.

4. Desert Soil: A large part of Rajasthan and adjoining states is covered with sand dunes.Dune sand is uniform in gradation.The size of particles is in the range of fine sand. This sand is non-plastic and highly pervious.

5. Marine Deposite: Marine deposite are mainly found in the South-West coast of India.These soil are thick layers of sand above deep deposits of soft marine clays.They contain a large amount of organic matter.The marine clays are soft and highly plastic.