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Assessment Of Soil Degradation
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Rapid Population growth affects the natural resource base through
increased demand for food, water, arable land and other essential
materials, such as firewood among others, thereby facilitating
encroachment into forests and woodlands as well as increasing demand
for fossil fuels and other resources. The poor or low soil quality
base arises due to two major factors. With few exceptions, growth in
human population have led to a reduction in the per capita land
availability and a breakdown of the erstwhile traditional natural
fallow system that used to be the means of replenishing soil fertility.
The methods used to restore the fertility of soils and to2sustain
agricultural productivity under traditional shifting agriculture have
become ineffective, and in some cases, have disappeared altogether. As
high potential land becomes less available and the rural human
population increases, farming is extending into more fragile lands,
undermining the natural resource base as well as undermining the
continued ability to produce food for the teeming populations.
Degradation of the natural resource base in tum impinges on the
livelihoods of all, but particularly rural communities. More small
farmers are forced to work harder, often on shrinking farms on marginal
land, to maintain household incomes.
Soil degradation, and in
particular the decline of soil chemical fertility, is a major
concern in relation to food production and the sustainable management of
land resources. It also affects land use/land cover but the spatial and
temporal effects of soil fertility change and its interaction with
land use/land cover change remains to be investigated.
Land use
involves the manner in which the biophysical attributes ofthe land are
manipulated and the intent underlying such manipulation for which the
land is used, whereas land cover implies to the biophysical state of the
earth's surface and immediate subsurface including biota, soil,
topography, surface and groundwater, human structures etc (Meyer et
al., 1994; Lambin et al., 2003). Land use change implies the conversion
of land use due to human intervention for various purposes such as
agriculture, settlement, transportation, e t c (Williams, 1994; Meyer,
1994; Turner et al., 1995). While land cover change on the other hand,
refers to modification of the existing land cover or complete conversion
of biophysical cover of the land to a new land cover type (Solomon,
2005).
Though people have been using and modifying land to obtain
food and other essentials for thousands of years, current rates, extents
and intensities of Land use/land cover change are far greater than ever
in history, resulting in unprecedented changes in ecosystems and
environmental processes at local, regional and global scales (Lambin et
al., 2003).
The area under crop cultivation in the world has
increased globally from an estimated 3 00-400 million ha in 1 700 to 1
500-1800 million ha in 1 990, a 4.5- to fivefold increase in three
centuries and a 50% net increase just in the twentieth century. The
area under pasture increased from around 500 million ha in 1700 to
around 3 1 00 million ha in 1990 (Ramankutty et al., 2002b). These
increases imply to changes, clearances or conversions of forests cover
and the transformation of natural grasslands, steppes, and savannas.
Forest area decreased from 5000-6200 million ha in 1 700 to 4300-5300
million ha in 1 990. Steppes, savannas, and grasslands also experienced a
rapid decline, from around 3200 million ha in 1700 to 1 800-2700
million ha in 1990 (Ramankutty et al., 2002b)
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