Soils

What is Soil? Soil is the surface of the earth’s crust where plants have their roots and where many small animals make their home. It is also a result of the breakdown of rocks.

Formation of Soil Soil is formed when rocks break down into very small particles by various processes such as weathering. There are two types of weathering: Physical Weathering and Chemical Weathering. Physical Weathering arises from the heating and cooling, the wetting and drying, and the freezing and thawing of the land. These actions cause alternate expansion and contraction of rocks which eventually cause the rocks to crack. Factors which play important role in physical weathering include: * Erosion by wind and water. * The action of plants, for example, cracks caused by penetrating roots. * The action of animals, for example, worm casts formed by earthworms. * Human interference. Chemical Weathering is the breakdown of rocks using a solvent that is able to dissolve the mineral structure. Chemical weathering is due largely to the oxidation and reduction of the elements in the soil. Oxidized rocks break up to form soil easily. Solution of minerals in the rocks helps in weathering. For example, when carbon dioxide dissolves in rain water it forms a weak solution of carbonic acid which can dissolve rocks which contain lime. Hydrolysis is another chemical action which causes rocks to break up into soil. The physical and chemical weathering agents and the living organisms in the soil determine the characteristics of the soil.

Components of Soil Soil is composed of different components. However there are main components which each soil contains. The proportion of each component determines the soil type. The main components include, soil water, soil air, soil organisms, humus, rock particles and mineral salts.
Soil Water: Soil water exists as a thin film around soil particles and occupies the air spaces between soil particles