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About 2 billion ha of the world’s agricultural land have been
degraded because of deforestation and inappropriate agricul-
tural practices (Pinstrup-Andersen and Pandya-Lorch, 1998).
In spite of global improvements on some parts of the land,
unsustainable land use practices result in net losses of crop-
land productivity – an average of 0.2%/year. The combined
effects of competition for land from growing populations,
reduced opportunity for migration and rotation along with
higher livestock densities, result in frequent overgrazing and,
hence, loss of long-term productivity. Satellite measurements
show that between 1981 and 2003, there was an absolute
decline in the productive land area (as Net Primary Produc-
tivity) across 12% of the global land area. The areas affected
are home to about 1–1.5 billion people, some 15–20% of the
global population (Bai
et al
., 2007).
LOSS OF CROPLAND AREA FROM LAND DEGRADATION
A number of authors including den Biggelaar
et al
. (2004) estimate
that globally, 20,000–50,000 km
2
of land are lost annually through
land degradation, chiefly soil erosion, with losses 2–6 times higher
in Africa, Latin America and Asia than in North America and Eu-
rope. The major degrading areas are in Africa south of the Equator,
Southeast Asia, Southern China, North-Central Australia and the
pampas of South America. Some 950,000 km
2
of land in Sub-Sa-
haran Africa is threatened with irreversible degradation if nutrient
depletion continues (Henao and Baanante, 2006). In most parts
of Asia, forest is shrinking, agriculture is gradually expanding to
marginal lands and land degradation is accelerating through nutri-
ent leaching and soil erosion. In fact, about 20% of the agricultural
land in Asia has been degraded over the last several decades (Foley
et al
., 2005). The pace of degradation is much higher in environ-
mentally fragile areas, such as on the mountains.