Africa is the hottest continent, and the climatic zones in which it is located are varied - from deserts to rainforests. The soils of the continent are also different. The diversity is explained by the amount of precipitation and the period of precipitation. Let's consider the characteristics of African soils, which types are most typical for the continent and their economic use.
Peculiarities
For soils in the tropical zone, the laterite formation process is typical.The soils of humid equatorial forests are red-yellow (the red color is given to the soil by iron oxide), highly permeable to moisture and air, thick, but contain little humus, although the top layer of organic matter decomposes quickly. Groundwater comes close to the surface. In the west of the Congo Basin, due to the slow flow of rivers, lateritic soils become gley, and tropical swamp soils occupy a large area.
To the north and south of the central part of the continent, red-yellow soils turn into red soils, which develop under humid savannas and evergreen forests. Red-brown soils occupy large areas in the south and southeast of Africa.
The map shows that tropical deserts are occupied by primitive, gravelly or pebble soils, semi-deserts are gray soils, and in oases there are alkali-saline and saline soils. Closer to the Mediterranean coast, brown soils form in the humid regions of the Atlas and Cape Mountains, and gray-brown soils with a high content of gypsum and carbonates form in dry regions (the coasts of Egypt and Libya).
What soils are typical for Africa?
African soils diverge symmetrically in both directions from the equator.
Reds
These are the predominant soils of savannas and are formed as a result of processes of constant change from wet to dry climates. In regions where there are more wet days than dry days, cracks form on the surface. There is little humus in red soils; they are acidic due to leaching processes. In those regions where there are more dry days, the soil darkens and becomes more humus.
The red color of African soil is the result of a high content of iron oxides; the percentage of humus reaches 1.5 to 2%, and fulvic acids predominate in its composition.In the northern part, closer to the desert, the soil gradually turns reddish-black.
During the drought period, the soil takes on a lumpy appearance, during the rainy season it is washed away, and erosive processes actively operate in it. Under the upper horizon there is a dense layer that does not allow moisture to pass through well; minerals washed out from above remain in it.
Red-brown
Soils of this type are formed under typical dry savannas and tropical woodlands in the eastern part of the continent. Here the dry season lasts 6-7 months, 80-1200 mm of precipitation falls per year, such conditions (stable high temperature and alternating dry and wet seasons) form soil consisting of layers of different properties, composition and morphology.
The upper horizon is light in granulometric composition, sandy or sandy loam, it is moisture-absorbing and allows water and air to pass through well. Beneath it there is a dense, very weakly structured clay layer. It is impregnated with iron oxides. Beneath it there is a horizon with a large content of nodules of lime and iron oxides. A large percentage of iron in all layers of the soil gives it a specific color.
Primitive, crushed stone or pebble
These are the soils of tropical deserts; they are located mainly in the northern half of the continent; in the southern part of the desert they stretch in a narrow strip near the western edge of the continent. They are completely infertile, structureless and often saline over large areas. Lime and gypsum crusts ranging in thickness from a few centimeters to 1-2 m are common.
Solonchak and alkali-solonchak
The upper layers of this type of soil contain a lot of easily soluble salts, which makes them almost unsuitable for vegetation growth.The morphological structure of saline soils in Africa is expressed in the fact that in the upper horizon there is a concentration of salts in the form of a crust or a loose layer of whitish-gray or white color. In the soil profile, salts are in the form of fine-crystalline accumulations in the form of shiny veins or inclusions.
The accumulation of salts occurs due to the evaporation of moisture coming from nearby and mineralized groundwater. The solonchak layer contains almost no humus; beneath it there is soil-forming rock, also saline. Salt marshes can have different thicknesses, but they always contain easily soluble salts with a percentage of 5-15%. Their maximum number is located near the surface, usually in the crust, but the deeper they go, the more their number decreases.
Serozems
They are formed in a dry subtropical climate on loams. These are loose, light-colored soils with a high content of carbonates on the surface. Gray soils contain more than 4% humus; this layer does not exceed 50 cm. Soils of this type require the application of mineral fertilizers to increase their productivity.
Brown, gray-brown, enriched with carbonates and gypsum
Brown African soils form under hard-leaved forests and shrubs in the northwest and southwest of the continent. Usually they are loamy or heavy loamy; if the soil is formed on dense sedimentary rocks, the profile thickness reaches 1 m; on loose rocks the thickness is greater. Humus in brown soils in the top layer is up to 5%; it is also found at a depth of 1 m, where its content is 1%. Soil differentiation by iron or aluminum is weakly expressed.The acidity reaction in the humus layer is neutral, but as you move down, the acidity increases.
The gray-brown soil develops in the dry subtropics, under arid shrub and herbaceous vegetation. The gray-brown soils of Africa are formed under conditions of non-percolative water regime and low groundwater levels.
The morphological structure of the soil is as follows: at the top there is a humus layer 20-25 cm thick, heavy loamy. It gradually transforms into a second horizon 0.5-1 m thick, dense, small-blocky structure, with a high content of carbonates, which are presented in the form of veins. In the next layer, the carbonates are even larger and are visible in the form of spots and nodules. The parent rock also contains carbonates and is usually saline.
Application of soils
African savannas are favorable for agriculture; significant areas have been cleared and plowed. The crops grown here are cotton, corn, peanuts, tobacco, rice, and sorghum. They are also used as pastures.
Citrus fruits, grapes, fruit crops, and coffee are grown on brown and gray-brown soils. To increase productivity, agricultural techniques are used: irrigation, application of fertilizers, organic and mineral, and measures are taken against erosion. In the oases, date palms, figs, fruit and olive trees, citrus fruits and some types of vegetables are cultivated.
The humus content of most African soils is low, which is why they are not very fertile in their natural state, but can be used for growing crops subject to constant irrigation, the use of fertilizers and other measures to improve fertility.
