Kenya land use and rain-use efficiency
Sub-Saharan Africa is particularly impacted by land degradation. In South Africa, production decreased overall; 29% of the coun-
In Kenya, over the period 1981–2003, despite improvements in try suffered land degradation, including 41% of all cropland
woodland and grassland, productivity declined across 40% of (Bai and Dent, 2007a); about 17 million people, or 38% of the
cropland – a critical situation in the context of a doubling of the South African population, depend on these degrading areas.
human population over the same period (Bai and Dent, 2006). (Source: Bai and Dent, 2007).
Trend in biomass in –2003
(left) and in rain-use efficiency
(RUE) in –2002 (right). De-
creases in RUE could be due to
various factors, including degra-
dation and run-off, soil evapora-
tion, increasing depleted soils,
overgrazing by livestock or other
forms of range degradation.
Left map
Red urban
Yellow cropland
Green grassland
Purple woodland
Blue water
Right map
Red major decline
Yellow moderate decline
Courtesy of ISRIC, Bai ZG and Dent DL (2006)
Green improvement
fertility were estimated at 22 kg nitrogen (N), 3 kg phosphorus tries productivity has declined in over 40% of the cropland area
(P), and 15 kg potassium (K) per ha. In Zimbabwe, soil erosion in two decades while population has doubled. Overgrazing of
alone results in an annual loss of N and P totalling US$1.5 billion. vegetation by livestock and subsequent land degradation is a
In South Asia, the annual economic loss is estimated at US$600 widespread problem in these regions.
million for nutrient loss by erosion, and US$1,200 million from
soil fertility depletion (Stocking, 1986; UNEP, 1994). The productivity of some lands has declined by 50% due to soil
erosion and desertification (Figure 16). Yield reduction in Afri-
Erosion is very significant in land degradation. On a global ca due to past soil erosion may range from 2–40%, with a mean
scale, the annual loss of 75 billion tonnes of soil costs the world loss of 8.2% for the continent. Africa is perhaps the continent
about US$400 billion/year (at US$3/tonne of soil for nutrients most severely impacted by land degradation (den Biggelaar et
and US$2/tonne of soil for water), or approximately US$70/ al., 2004; Henao and Baanante, 2006), with the global aver-
person/year (Lal, 1998). It is estimated that the total annual age being lower, possibly in the range of 1–8%. With increasing
cost of erosion from agriculture in the US is about US$44 bil- pressures of climate change, water scarcity, population growth
lion/year or about US$247/ha of cropland and pasture (Lal, and increasing livestock densities, these ranges will be prob-
1998). In Sub-Saharan Africa it is much larger; in some coun- ably conservative by 2050.
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