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| Soil |
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| Soil can be defined as the uppermost crust of earth mixed with organic material and in which animals and microorganisms live, and plants grow. 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. Formation of soil takes place by interaction between the physical and biological components. |
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| Inorganic or mineral constituents are derived from the soil forming rocks, by fragmentation or weathering. Rocks are affected by the action of rain, wind and temperature. This is physical weathering. Lichens and mosses grow on rocks also causing weathering. |
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| 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. |
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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 that 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, major and minor, to plants for their growth and development, circulating 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). Some of the fungi also fix phosphorus (mycorrahage). |
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| Soil is classified based on nature and composition, into the following: |
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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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| Soil's fertility is its capacity to sustain plant life with required nutrients. |
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 Fertility of soil decreases when the same crop is grown in the same land repeatedly, or by soil erosion. Erosion is the physical removal of soil particles from their original places and transportation to some other places |
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 Soil fertility can be prolonged by human efforts (application of manures, bio-fertilizers, chemical fertilizers to soil of crop fields etc.) and by natural processes. |
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