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Soil: The word ‘soil’ is derived from a Latin word, “Solum”, meaning ‘floor’. Soil is a complex system made up of mineral matter, organic matter, and soil water and soil air. Therefore, it contains not only the solid and liquid phases but also the gaseous phase.

Soil is a thin layer of earth’s crust which serves as a natural medium for the growth of plants. Soil is the unconsolidated mineral material on the immediate surface of the earth that serves as a natural medium for the growth of land plants. Soil is the unconsolidated mineral matter that has been subjected to, and influenced by genetic and environmental factors, parent material, climate, organisms and topography all acting over a period of time. Soil is a natural body, synthesized in profile form from a variable mixture of broken and weathered minerals and decaying organic matter which covers the earth in a thin layer and which supplies when containing the proper amounts of air and water, mechanical support and in part, sustenance for plans.

Some definitions of the soil,

According to Joffe (1949),”The Soil is a natural body of minerals and organic constituents differentiate into horizons of variable depth, which differs from the materials below in morphology, physical make up, chemical properties and composition and biological characteristics.”

Soil is a dynamic natural body developed as a result of pedogenic processes during and after weathering of rocks, consisting of minerals and organic constituents, possessing definite chemical, physical, mineralogical and biological properties having variable depth over surface of the earth and providing medium for plant growth of land plants.

The soil is heterogeneous, polyphasic, particulate, disperse and porous system, in which the interfacial area per unit volume can be very large. The disperse nature of the soil and its consequent interfacial activity give rise to such phenomena as:

1. Absorption of water and chemical,     
2. Inoic exchange,
3. Adhesion
4. Swelling and Shrinking,         
5. Dispersion and Flocculation and
6. Capillary.

Functions of soil:

1. Soil provides anchorage to root enabling plants to stand erect.
It acts as a store house of water and nutrients for plant growth.
3. It acts as an abode of flora and fauna which suitably transform nutrients for uptake by plant roots.
4. It provides space for air and accretion which creates healthy environment for the biological activity of soil organisms.

Soil is natural body, differentiated into horizons of mineral and organic constituents, usually unconsolidated, of variable depth, which differs from the percent material below in morphology, physical properties and constitution, chemical properties and composition and biological characteristics.

Soil profile:  The vertical exposure of soil with its various layers (horizons) Or

A vertical section through the soil is called as the soil profile.
The various distinguishable layer of soil that occurs are called horizons.

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