Major Soil Types of Africa – Soils in Africa and the World (Senior 3 Geography) | Ganzaa

Soils in Africa and the World

Lessons

Senior 3 · Geography

Soils in Africa and the World

4 lessons

Lesson 3 of 4

Major Soil Types of Africa

25 min

Let's begin

Between the Blue Nile and the White Nile in Sudan lies the Gezira, one of the largest irrigation schemes in Africa. Water flows to the farms by gravity along canals, and the soil holds it well because it is very rich in clay. A few hundred kilometres away, in the Sahara, the same water would sink into sand. Africa's soils differ as much as its climates, and the map below shows how closely the two patterns match.

Figure 5. The main soil zones of Africa, simplified. Drawn by Ganzaa.

Definition

Zonal soils: soils whose character is set mainly by the climate and vegetation of a large zone, e.g. latosols and desert soils.

Intrazonal soils: soils in which a local factor, such as waterlogging, salt or an unusual rock, outweighs the climate, e.g. black cotton soils and volcanic soils.

Azonal soils: young soils without proper horizons, e.g. alluvial soils on recent river deposits and thin, stony mountain soils.

The main soil types of Africa

Soil type (international name)	Where	Characteristics	Use and problems
Latosols, or tropical red earths (ferralsols)	Congo Basin; Guinea coast (Liberia, Sierra Leone); eastern Madagascar; parts of Angola and Zambia	Very deep, red or yellow, rich in iron and aluminium oxides; acid and strongly leached	Support rainforest and tree crops such as oil palm and cocoa; lose fertility fast when cleared; may harden into laterite
Savanna soils, red and brown (lixisols and related soils)	The savanna belts north and south of the forest, and much of East Africa	Red to brown, moderately deep, leached in the wet season; iron-rich crusts in places	Cereals (maize, sorghum, millet), groundnuts, cotton and grazing; easily eroded when bare
Black cotton soils (vertisols)	Central Sudan, Ethiopia, the Lake Chad area, parts of Kenya and South Africa	Dark, heavy clay that swells when wet and cracks deeply when dry	Fertile; cotton and sorghum, irrigated in the Gezira; sticky and hard to plough, waterlogs in the rains
Volcanic soils (andosols)	Ethiopian Highlands; slopes of Kilimanjaro, Mount Kenya, Mount Elgon, Mount Cameroon and the Virunga volcanoes	Dark, light and porous, formed from volcanic ash; hold water well	Among Africa's most fertile soils: coffee, tea, bananas, potatoes; attract dense farming populations; erode on steep slopes
Desert soils (arenosols, leptosols and others)	Sahara, Horn of Africa, Namib and Kalahari	Sandy or stony, very little humus, often salty or with hard lime crusts	Grazing by nomadic herders; crops only where irrigated, as at oases
Alluvial soils (fluvisols)	Nile valley and delta; inland delta of the Niger; river floodplains	Fine silt and clay laid down by rivers; young, layered, fertile	Intensive irrigated farming; can flood or become salty if drainage is poor
Mediterranean soils	Coasts of Morocco, Algeria and Tunisia; south-western Cape	Red-brown, moderately fertile, often on limestone	Wheat, olives, citrus fruit and grapes

A vertisol profile: dark, heavy clay split by vertical cracks. In East Africa these are called black cotton soils. Photo: USDA, public domain, via Wikimedia Commons.

Linking soils to climate and relief

Going north or south from the Equator, the soils follow the climate belts: latosols under rainforest, savanna soils where there is a dry season, then desert soils where rain is rare, and Mediterranean soils at the far north and south.
Volcanic soils break this pattern: they follow the volcanoes of the rift and the highlands, not the climate.
Black cotton soils form on flat, badly drained plains with a long dry season, and alluvial soils along rivers that flood.
On the slopes of every hill, the catena adds local variety, as you saw in lesson 1.

Worked example

Worked example 1: reading Figure 5. Name the main soil type and suggest one use at each place: (a) the Congo Basin, (b) the Nile valley in Egypt, (c) the central Kalahari, (d) the slopes of Mount Kenya.

Place	Soil	Use
(a) Congo Basin	Latosol	Rainforest; tree crops such as oil palm
(b) Nile valley	Alluvial soil	Irrigated cotton, wheat and vegetables
(c) Central Kalahari	Desert (sandy) soil	Grazing
(d) Mount Kenya	Volcanic soil	Coffee and tea

Worked example

Worked example 2: explaining a soil. Explain why black cotton soils are fertile but difficult to farm.

Fertile: they are rich in clay minerals that hold plant nutrients and water, and they are not strongly leached, because the climate has a long dry season.
Difficult: the same clay swells and becomes sticky in the rains, so ploughs and feet sink and the ground waterlogs; in the dry season it shrinks, cracks deeply and sets hard.
So they give good yields where farmers can control water, as with irrigation in the Gezira, and are hard work elsewhere.

Warning

Red is not always rich. Many pupils think a deep red soil must be fertile. The red colour comes from iron oxides left behind after strong leaching, so latosols are often poor in nutrients. The dark colour of volcanic and black cotton soils is a better (though not perfect) sign of fertility.

Tip

Follow the rain. To remember Africa's zonal soils, travel from the Equator to the Sahara: wet all year (latosols) → wet and dry seasons (savanna soils) → almost no rain (desert soils) → winter rain on the coast (Mediterranean soils). Then add the "exceptions": volcanoes, rivers and badly drained clay plains.

Practice

Name the soil type found in the Congo Basin and give two of its characteristics.
Where in Africa are black cotton soils found? Name two areas.
Why are volcanic soils important for farming in East Africa?
Give one difference between zonal and azonal soils, with an African example of each.
Describe how soil changes from the Equator northwards to the Sahara.
Why are alluvial soils along the Nile so important to Egypt?
Explain why latosols lose their fertility quickly after the forest is cleared.
A government wants to grow more food. It can develop irrigation on a black cotton plain or clear rainforest on latosols. Which would you advise, and why?

Show answersHide answers

Latosol (ferralsol): deep; red or yellow; rich in iron and aluminium oxides; acid; strongly leached and low in plant nutrients (any two).
Any two: central Sudan (the Gezira), Ethiopia, the Lake Chad area, parts of Kenya, parts of South Africa.
They are dark, porous and very fertile and hold water well, so they support crops such as coffee, tea, bananas and potatoes, and many people farm them.
Zonal soils are shaped mainly by climate and vegetation and cover large zones (e.g. latosols of the Congo Basin); azonal soils are young and lack proper horizons (e.g. alluvial soils of the Nile valley).
Latosols under the equatorial forest; then red and brown savanna soils where there is a dry season; then thin, sandy or stony desert soils in the Sahara.
Almost all of Egypt is desert; the alluvial soils of the valley and delta are fertile and can be irrigated with Nile water, so they grow most of the country's crops.
Most nutrients are in the living forest and its thin humus layer. Clearing ends the supply of leaves; heavy rain leaches the bare soil; what is left is poor and may harden into laterite.
Usually the black cotton plain: the soil is naturally fertile and holds water, so irrigation can give good yields for many years, as in the Gezira, though drainage must be managed. Clearing rainforest gives good yields for only a few years before leaching ruins the soil, and destroys the forest. (Accept a well-argued alternative.)

Sources and credits

Ferralsol, Vertisol, Andosol and Gezira Scheme: Wikipedia contributors, Wikipedia, CC BY-SA 4.0, adapted by Ganzaa.
Figure 5 is simplified from the Global Soil Regions map, USDA Natural Resources Conservation Service, public domain; outlines from Natural Earth, public domain.
Photo: Vertisol, USDA, Wikimedia Commons, public domain.

Figure 5, the worked examples and the practice exercises are written by Ganzaa.

This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.

1The main soil types of Africa

2Linking soils to climate and relief

The main soil types of Africa

Linking soils to climate and relief