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1.7 Soil Degradation 25

as a result of soil erosion and desertification. Yield reduction in Africa due to past
soil erosion may range from 2 to 40 %, with a mean loss of 8.2 % for the continent
(Lal 1995 ). There are also serious productivity losses (20 %) due to erosion in Asia,
including India, China, Iran, Israel, Jordan, Lebanon, Nepal, and Pakistan (Dregne
1992 ). Soil compaction has caused yield reductions of 25–50 % in some regions of
Europe (Eriksson et al. 1974 ) and North America and between 40 and 90 % in West
African countries (Charreau 1972 ; Kayombo and Lal 1994 ). In Ohio, reductions in
crop yields are 25 % in maize, 20 % in soybeans, and 30 % in oats over a 7-year
period (Lal 1996 ).

1.7.1 Causes of Soil Degradation

Soil degradation may result from natural causes and human-induced causes.
Topographic and climatic factors such as steep slopes, frequent fl oods and tornadoes,
storms and high-velocity wind, high-intensity rains, leaching in humid regions, and
drought in dry regions are among the natural causes. Deforestation and overexploi-
tation of vegetation, shifting cultivation, soil desurfacing, overgrazing, indiscrimi-
nate use of agrochemicals and lack of soil conservation practices, and overextraction
of ground water are some anthropogenic causes of soil degradation.
The principal cause of land degradation is the non-appropriate land use.
Economic and social problems, population pressure, poverty, land tenure system,
farming systems, lack of technical advice, use of improper implements, etc. are the

reasons of this mismanagement. GLASOD identifi ed five main causes of human-
induced soil degradation worldwide: deforestation, overgrazing, mismanagement of
agricultural land, overexploitation, and bio-industrial activities. The causes of soil
degradation are elaborated in the following sections.

1.7.1.1 Deforestation

Deforestation refers to the conversion of a forest into a non-forest use such as farm-
land, ranches, pasture, industrial complexes, and urban areas (Fig. 1.3 ). The world’s
total forest area is just over four billion hectares. Seven countries (Russia, Brazil,
Canada, the USA, China, Indonesia, and the Democratic Republic of Congo)
account for more than 60 % of the total forest area. Ten countries or areas have no
forest at all, and an additional 54 countries have forest on less than 10 % of their
total land area (FAO 2010 ). About one-half of the forests that covered the earth have
been cleared (Kapos 2000 ). Each year, another 16 million hectares disappears. The
World Resources Institute ( 1997 ) estimates that only about 22 % of the world’s
original forest cover remains intact – most of this is in three large areas: the Canadian
and Alaskan boreal forest, the boreal forest of Russia, and the tropical forest of the
northwestern Amazon Basin and the Guyana Shield (Guyana, Suriname, Venezuela,
Columbia, etc.). For millennia, humankind has influenced the forests, and the