World’s Soil Resources

Figure 9.12 Actual water erosion prediction map of South Africa. Source: Le Roux et al., 2012.
The erosion process starts when the vegetation cover is disturbed or removed, allowing the rainfall to
impact directly on bare soil. If measures to restrict surface run-off are not put in place, the effect is generally
two-fold: firstly, the water flowing on the soil surface removes a significant amount of topsoil (‘sediment’),
especially on steeper slopes; and secondly, the duplex nature of the soils (sandy topsoil abruptly overlying a
structured clay subsoil) results in the formation of a surface seal. As a result, very little water is actually able to
infiltrate the soil. Research in South Africa (Levy, 1988; Rapp, 1998; Bloem, 1992) indicated that exchangeable
sodium percentage (ESP) values play an important role in erosion risk, with problematic values being over 12,
although values as low as 5 or 6 (Bloem and Laker, 1994; Laker and D’Huyvetter, 1988) can also cause erosion
under poor land use conditions.
Combating soil erosion by water remains a huge challenge in many affected areas of the country due to
a combination of lack of resources, poor knowledge or awareness and poor infrastructure, mainly roads.
The challenges of treating erosion and the more difficult task of rehabilitating large areas of land, combined
with the off-site effects such as silting up of dams, together pose one of the most serious soil management
challenges in South Africa today.
Soil nutrient depletion, acidity and organic matter
Although soil erosion by water was confirmed as the main soil degradation type in the country, there are
areas in South Africa affected by wind erosion, nutrient depletion, loss of organic matter, soil acidity, salinity
and sodicity as well as pollution from mining and industrial sources. Desktop assessments of soil nutrient
depletion, acidity and organic matter in South Africa were conducted during 2007-2008 (Beukes, Stronkhorst
and Jezile, 2008a,b; Du Preez et al., 2010; Du Preez et al., 2011a,b; Rantoa, Du Preez and Van Huyssteen, 2009).
Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes
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in Africa South of the Sahara