May 022013

Soil is a dynamic natural body on the surface of the earth in which plant grow and is composed of minerals and organic materials and living forms. It is usually differentiated into horizons from mineral and organic constituents of variable depth which differ from the parent material below in morphology, physical properties and constituents, chemical properties, composition and biological characteristics.
Soil is an organized mixture of minerals, organic materials, living organisms, air and water.

Composition of Soil

The Soil consists of 4 major components and these components cannot be separated with much satisfaction because they are presenting very intimately mixed with each other.

The composition of soil is:-

  • Organic matter 5%
  • Inorganic or mineral matter 45%
  • Soil water 25%
  • Soil Air 25%

In fact soil is a mixture of various organic and inorganic chemical compounds.

Organic matter of soil
Soil organic matter represents partially decayed and partially synthesised plant and animal reduces. Such organic reduces are being broken down by the action of soil micro organisms .The organic matter content in the soil is very small and varies from about 3-5% by in the top soil.
The most important characteristics of organic matter in the soil are as follows:-

  • It improves the physical condition of the soil.
  • It increases the water holding capacity of the soil.
  • It is a major source of nutrients, i.e. nitrogen, phosphorous and sulphur.
  • It is the main source of energy and soil organism.
  • It is responsible for moist desirable surface soil structure.
  • It promotes a greater proportion of large pore sizes.
  • It improves aeration status of the soil.

Inorganic matter in soil
Minerals are naturally occurring inorganic solid homogenous substances compound of atoms having an orderly and regular arrangement with definite composition and a characteristic geometric form.
The rocks which form the earth are made up of minerals. Rocks are mixtures of two or more minerals. So the physical and chemical composition of rocks varies with the characteristic of the minerals.
Rocks are generally 3 types they are Igneous Rocks, Sedimentary Rocks and Metamorphic Rocks.

Types of Soil
Soil are classified into six major based on their nature and composition
1-Red Soil:-
Red Soil are found in Andhra Pradesh, Tamil Nadu and parts of Bihar, Odisha, UP and West Bengal.
Their colour is due to high proportion of iron components.
These are mainly sandy to loam in texture with gravels on upper slopes, sandy soils, deeper loamy soils on Lower slopes and clay in the valley bottoms.

2-Laterite soils or Latosols:-
These are present in Western Ghats, Easteren margins of Chhota Nagpur plateau, Maghalaya few patches around Kathiawar, North Bangalore and West Hydrabad.These soil are porous clay rich in hydroxides of iron and aluminium. At low elevations, such soils are suitable for paddy cultivations , where as those at higher elavations, favour the growth of coffee, rubber, tea and cinchona.

3-Black Soil:-
This type of soil is found in the deccan traps including Maharashtra, Mysore and MP.

4-Skeletal (Mountain Soil):-
They occur in north-western hills on the Aravallis, where they are stony sandy hillfoot fans and slope colluviums, and in the humid south and east of the Himalaya and in the Meghalaya.

5-Desert Soil:-
These soils are found in the Rajasthan and the semi-desert areas of the Rann of Kutch.

6-Alluvial Soil:-These occur chiefly in the indo-Gangotri Plain covering the states of Punjab and Haryana in the north-west, UP and Bihar .These soil is rich in loams and clay components in Punjab and western Ganga plains


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