The word soil is derived from Latin word 'solum' meaning earthy material in which plants grow. The soil is the consolidated outer layer of the earth's crust ranging in thickness from a mere film to three metres or more. It provides mechanical anchorage to plants, besides being a reservoir of water and plant nutrients. The soil also supports a rich and highly diversified micro-flora and fauna.
Typically, soil is a complex mixture of inorganic and organic materials. The inorganic materials, that is, the mineral constituents of soil are derived from parent material (the soil forming rocks) by fragmentation and weathering. The pore spaces formed between the mineral particles of soil are filled with water and gases. The organic components of soil comprise organic wastes, dead remains of plants and animals, and their decomposition products. Besides, a large variety of algae, bacteria, fungi and many small and large animals are invariably present in a fertile soil.