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Natural Environment

Soils

- Soil-Forming Processes -

- Major Soil Types -

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Like vegetation zones, soil regions in Africa are closely linked to climatic zones. Rainfall and temperature determine the growth of vegetation, which inhibits soil erosion and enriches soil with nutrients from decaying organic material, called humus. The luxuriant vegetation of tropical forest environments produces large quantities of humus, which is concentrated on the forest floor. In savanna grasslands, humus extends to a greater depth in the soil. The sparse vegetation of semidesert and desert regions gives rise to soils with little organic content. Rainfall and temperature also determine the intensity of chemical weathering, physical weathering, and leaching—all of which affect the development of soil types.

Soil development is highly influenced by the soil’s parent material—the rock from which it is derived—and by topographic relief. Much of Africa’s soil is derived from ancient, quartz-rich rocks that produce generally infertile soils with high sand content. Soils formed in areas of younger volcanic bedrock tend to have higher clay and mineral content, and are therefore more fertile. Relief plays a major role in soil erosion, especially by water. Erosion removes topsoil from upper slopes and deposits eroded materials downslope. These erosion and deposition processes often create a gradation of soil types along a slope. African farmers take advantage of these variations in soil type and soil fertility by planting different crops at different levels of the slope.

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