Soil or edaphic factors as related to
• the type of soil particles
• the humus, mineral and air content,
• the pH, and
• the depth of the water table.
Besides climatic factors , soil factors also plays an important role in determining the vegetation of a region. They account for the variation in the type of plants that are found in regions with similar climates.
Natural soil types :
Natural soils are influenced by rainfall and temperature. Heavy rainfall causes the soil to become leached, I.e. soluble minerals are washed into deeper layers out of reach of plants roots. High temperature increases the rate if decomposition of organic matter in the soil, thereby lowering it's humus content. Thus, climatic conditions tend to produce poor soils in the tropics and rich soils in the temperate regions. Besides climate and vegetation, the parent rock material also contributes to the quality of the soil. For example, volcanic rocks tend to produce fertile soils.
Laterite, a red soil which is a product of leaching, is commonly found in the tropics. It is composed mainly of iron and aluminum compounds, and poor in humus and essential plant nutrients, such as phosphorus, nitrogen and potassium. The black and brown soils of the temperate grasslands are the works richest soils, with a high minerals and humid content. The light coloured desert soils tend to be very rich in minerals but have a low humus content.
In Nigeria, the soils are generally poor. Lateritic soils are widespread especially In the Guinea and Sudan belts. The soil of the costal regions are sandy or alluvial. These soils are also leached. The rain forest soils quickly lose their fertility under cultivation. In fact, the rain forests are a result of climatic conditions, not soil fertility. The brown soils of the north, around kano state, are relatively rich, and intensive agriculture is practiced in these regions.
