(a) Soil is defined as the uppermost layer of the earth crust in which plants get supports and food (or nutrient.
(b) The process of soil formation is called weathering. Weathering is defined as the breaking down of rocks into tir pieces to form soil
(c) The process of weathering involves three processes:
(i) Physical weathering
(ii) Chemical weathering
(iii) Biological weathering
(i) Physical Weathering: This involves the breaking down of rocks into tin pieces by special agents such as temperature, running water, ice,wind, pressure, etc.
(ii) Chemical Weathering; This involves the breaking down of rocks into tiny pieces by chemical means such as solution, oxidation, carbonation hydrolysis and hydration.
(iii) Biological weathering: Involves the breaking down of rocks by biological agent suc as earthworm, roots of plants, hooves of animals, rodents and the activities of man.
(c) Soil Profile: A vertical section cut across the soil to show the arrangement of layers is called soil profile. The different horizontal layers are called horizons and there are 3 main horizons in a well-weathered soil namely.
A - horizon
B - horizon and
C - horizon.
A Horizon: This is the top soil. It contains remains of plants and anima which have decomposed to form humus, it is also known as the alluvial horizon which is derived by the washing c clay and fine soil particles down the soil profile.
B - Horizon: This is zone of enrichment (alluvial horizon or accumulatic of soil minerals). The minerals have been washed down from the A- horizon and converted into inorganic compound It is regarded as the sub-soil
C - Horizon: This is the layer of underlying weathered debris. It is the source of pares material. It in underlain by hard unweathered rock.