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| Soil |
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| The word soil is derived from a Latin word solum meaning ground. It is a stratified mixture of inorganic and organic materials, both of which are products of decomposition. |
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| Inorganic component of soil i.e. mineral constituents are derived from the soil forming rocks, by fragmentation or weathering. Weathering of rocks takes place by two methods: |
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 Physical weathering - It is due to the action of rain, wind and temperature. |
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 Biological weathering of rocks - This is due to growth of lichens and mosses on the rocks. The organic component of the soil is formed either by microbial decomposition of dead remains of plants (litter) or animals, or through metabolic activities of living organism present in the soil. Thus the formation of soil takes place by interaction between the physical and biological components. |
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| Soil can be defined as the uppermost crust of earth, which is mixed with organic material and in which animals, and microorganisms live and plants grow. |
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 Inorganic material derived from parent (material) rocks |
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 Organic material derived from dead and decayed materials |
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 Biological system - such as bacteria, fungi, algae, protozoa and other soil animals such as nematodes, earthworms etc. |
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 The air and water occupying the pores between the soil particles, which are loosly packed |
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 Soil is the medium for plant growth, it provides anchorage to plants. |
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 Soil provides nutrients, both major and minor, to plants for their growth and development. Thus, it circulates the nutrients into biological system by means of mineral weathering. |
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 Soil harbours the microorganisms such as bacteria and fungi, which fix the free atmospheric nitrogen into soil (nitrogen fixation) and at the same time, some of the fungi also fix phosphorus (mycorrahage). |
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| Soil is classified based on nature and composition. They are: |
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 Alluvial soil - rich in loam and clay |
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 Black soil - mostly made of clay |
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 Red soil - sandy to loam |
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 Mountain soil - stony, sandy soil |
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 Desert soil - sandy and poor in organic carbon |
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 Laterite soil - porous clay, rich in iron and aluminium hydroxides |
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| Fertility of the soil is nothing but ability to nourish the plant life with required nutrients. The fertility of soil decreases when crop is grown in the same land repeatedly. Another cause of reduction of fertility of soil is soil erosion. Soil erosion refers to physical removal of soil particles from their original place and transportation to some other places. Soil fertility can be prolonged both by the human efforts (application of manures, bio-fertilizers, chemical fertilizers to soil of crop fields etc.) and natural processes. |
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| Note: |
Loamy soil has about 30-50% silt and 20% less than clay particles. |
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Sand contains rock particles with diameter in range 0.125-2.0mm. |
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Clay has soil particles whose size is less then 2-4 mm in diameter. |
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Silt soil is composed of particles whose diameter ranges from 1/256-1/16mm. |
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