Soil is a part of the earth's surface that contains disintegrated rocks and decaying organic matter. It provides support for the growth of many plants and animals.

Soil is formed from rocks by the following two processes:

(a) Weathering It is the process of breaking down of bigger rocks into smaller mineral particles.

Weathering occurs by three means:

(i) Physical weathering: It occurs because of climatic factors such as temperature, wind, rain water, ice and snow.

(ii) Chemical weathering: It occurs through chemical processes such as hydrolysis, hydration, oxidation and reduction. The primary end products of chemical weathering are silica, clay, inorganic salts and hydrated oxides.

(iii) Biological weathering: It is carried out by living organisms such as lichens and bryophytes. These three processes generate cervices in the rocks that act as places for soil build up.

(b) Paedogenesis (soil development): This process involves the decomposition of organic material by bacteria and fungi, thereby leading to humification and mineralisation. Addition of organic matter (humus) is the final stage of soil formation that occurs after the consumption of organic matter by detritivores.

A mature soil consist of minerals, organic matter, oxides of nitrogen, ammonium ions, water and air.