Leptosols
Shallow soil over hard rock or gravelly material (from
Greek leptos, thin).
Leptosols are shallow soils over hard rock, very gravelly material or highly calcareous deposits.
Because of limited pedogenic development, Leptosols have a weak soil structure. Leptosols occur all
over Africa, especially in mountainous and desert regions where hard rock is exposed or comes close
to the surface and the physical disintegration of rocks due to freeze/thaw or heating/cooling cycles
are the main soil-forming processes. In WRB, bare rocks exposes at the surface (possibly displaying
only microscopic soil formation) are referred to as Nudilithic Leptosols.
Lixisols
Lixisols are slightly acid soils that show a distinct increase in clay content with depth. The clay is predominantly
kaolinite with limited capacity to hold nutrients. Occurring mainly in the dry savannah region with low biomass
production, Lixisols do not hold much organic matter and lack a well developed soil structure. High-intensity
rainfall will destroy any soil structure present making Lixisols prone to erosion. If the soil is not protected, a
crust may develop which prevents rain entering the soil. Overland flow will then erode the topsoil which is the
most fertile part. Wind erosion may be an issue as loose soil particles at the surface can easily be blown away.
Left: Rock outcrops are typical of Leptosol
landscapes. Trees must be shallow rooting
or develop where the soil is a little deeper
and where impeded drainage can lead to
higher water retention. (EM)
Left: A cultivated Lixisol from Tanzania.
Note the use of sorghum stalks as a mulch
to protect the soil from erosion. (OS)
Below: Leptosol from Ethiopia - a cover
of debris some 20 cm thick overlies a
dolerite. Soil development is slow. Only
limited extensive grazing is possible. (JD)
Below: A characteristically red Lixisol
from Tanzania. (EM)
The map shows where Leptosols are
dominant. They cover around 17% of
Africa.
The map shows where Lixisols are
dominant. They cover around 4% of Africa.
Soil Taxonomy classifies most of these
soils as Alfisols.
Soil Taxonomy classifies most of these
soils as Entisols.
Luvisols
Slightly acid soils with a clay-enriched subsoil and high
nutrient-holding capacity (from Latin luere, to wash).
Luvisols have a distinct increase in clay content with depth as a result of clay movement from the upper
part of the soil to the lower part. The clay is usually a mixture of kaolinite, illite and montmorillonite,
giving the soil a high nutrient-holding capacity. In general, Luvisols have a well-developed soil structure,
which contributes to a good water-holding capacity. Luvisols in Africa are mainly found in the
Mediterranean region and in the southern and eastern parts of Africa on relatively young surfaces.
Left: Drip-irrigated cultivation on Luvisols
in Morocco. Note the virtual absence of a
darker coloured surface layer, indicating
that this soil is poor in organic matter.
(OS)
Slightly acid soils with a clay-enriched subsoil and low
nutrient-holding capacity (from Latin lixivia, washed-out
substances)
Nitisols
Deep red soils with a well developed, nut-shaped
structure (from Latin nitidus, shiny)
Nitisols develop mainly from basic iron-rich rocks such as basalt. Their main characteristics are a dark
red colour and a well-developed structure that is nutty in appearance with shiny surfaces. The active
iron content (i.e. amorphous iron oxides and hydroxides) is high, which enforces strong bonding of
soil particles and the formation of the nut-shaped aggregates. The shiny surfaces are a mixture of clay
and iron coatings. Most Nitisols are dominated by kaolinite clay. While common in eastern Africa, they
also occur in many other parts of Africa.
Left: Nitisols are much sought after
because of their high productivity despite
a high phosphate-fixing capacity. Coffee
crop on Nitisols in the highlands of Kenya.
(ISRIC)
Below: Red Luvisol from Botswana - note
the deep rooting and the much better
developed soil structure compared to the
Lixisosl. (ISRIC)
Below: Nitisols are mainly developed
in highly weathered products of basic
igneous parent rock. This Nitisol from
Benin shows a well-developed structure.
Rooting is limited to the upper part of
the soil due to strong acidity and high
aluminium toxicity in the subsoil. (OS)
Soil Taxonomy classifies most of these
soils as Alfisols.
Soil Taxonomy classifies most of these
soils as Oxisols.
The map shows where Luvisols are
dominant. They cover around 4% of Africa.
The map shows where Nitisols are
dominant. They cover around 2% of Africa.
The soil of Africa | Soil Atlas of Africa
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