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Composition of Soil

 

Composition of Soil

Soil

According to Soil Science Society of America, soil is defined as the unconsolidated mineral or organic matter on the immediate surface of the earth that serve as a natural medium for the growth of land plants.


Composition of soil

As far as the composition of the soil is concerned it is composed of four basic components:

  • Minerals-          45%
  • Organic matter 5%
  • Water-              20-30 %
  • Air-                  20-30%

The amount of these components of the soil depends on the quality of vegetation, soil compaction and water present in the soil.

But in reality the composition is very much complex and is dynamic in nature.

The above four components are categorized under two headings solid phase and non-solid phase.

Solid phase includes minerals and organic matter whereas non-solid phase consists of air and water, the later phase is quite stable in nature.

  • Minerals

Minerals are composed of weather product of parent rocks that are weathered over many thousands of years. The minerals are composed of following particles that are defined by the diameter of the constituent particles

Gravel about 2mm

Coarse sand 2mm to 0.2mm

Fine Sand 0.2 mm to 0.02 mm

Slit 0.02 mm to 0.002 mm

Clay below 0.002 mm

  • Organic matter

It consists of the remains of living organisms in various stages of decomposition as well as living microorganisms. Organic matter is present in un decomposed as well as decomposed form the latter is termed as humus. the amount of organic matter varies in different soils soils with good vegetation cover where plants and animal remains decompose continuously possess high content of organic matter

  • Soil water

Soil water is present in the intercellular spaces of the soil this water is held due to capillary action. Some of this water will steadily drain through the soil via gravity and enter into water bodies. The maximum amount of water that a soil can retain is referred to as field capacity.

  • Soil air

The pore spaces of the soil are filled partly with air and partly with water however the volume of the air varies inversely with that of water as the moisture content of the soil increases the air content decrease and vice versa.

 


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