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times, soil erosion occurs everywhere. In many countries, soil erosion is not
confined to a single field or single farm but affects a large area. It is grave
where the rate of removal exceeds that of replacement, and this happens on some
scale where the land is cultivated. In its extreme manifestations, soil erosion
shows itself in deep gullies, cut by torrents through the soil to the bedrock
and in huge areas stripped by the wind of their top soil and left as infertile.
has been most spectacular in the North American continent. In this continent,
large areas in the mountains have been laid waste by gullies. This had been
largely the outcome of deforestation.
Large areas in
Kansas, Nebraska and also in other states have lost their topsoil through wind
erosion because of tilling land that is marginal.
has caused unfair impact in Canada and has reached serious dimensions in
Venezuela, Brazil, Uruguay and Argentina.
marginal land has been destroyed by over cultivation and overgrazing of
the government has come to take a serious thought of the problem and is prompt to
restrict its ravages.
countries, endeavors have been made to make good some of the damage that has
been done, while in others it is too late, as in central Turkey, where many
hillsides have been eroded down to the bare rock.
destruction of forests has caused large- scale soil erosion in many countries.
The phenomenal growth of population is the main factor to exert pressure on the
existing forests of the world. Apart from these, because of the increasing
price of fossil fuels and increasing demand for additional farmlands for
cultivation, there has been rapid denudation of forests in many countries.
In Nepal, as
the population growth is on the high side, the depletion of forest has given
rise to soil erosion and other harmful consequences. As the forest area of the
country has dwindled compared to past decades, about two hundred and forty
million cubic centimeters of fertile soil are flushed down every year. Counting both the big and the small ones, there
are altogether six thousand rivers in the country which have their origins in
the lap of the Himalayas. They are
eternal sources of water and flow with great speed, especially during the rainy
season, eating away the soil of their banks.
A survey has
made it clear that about thirteen percent of the total land of our country has
been affected by soil erosion. Although some efforts have been made to check
soil erosion much remains to be done.
amount of soil erosion can be reduced by adopting various methods. One of the
simple traditional procedures is to keep the surface constantly covered by
vegetation. In fact, higher plants influence the soil in many ways. By
extending their roots into the soil, they act as binders and so prevent erosion
from taking place, with grasses being particularly effective in this role.
Shifting cultivation is also a
traditional method of reducing soil erosion in the tropics by rotating the
location of the fields.
can be reduced to some extent by constructing terraces which restrict the speed
of moisture movement and increase greatly the infiltration on the flat surface.
This system not only reduces soil erosion but also stores moisture in the soil.
of erosion control is strip cropping which consists of narrow strips of two or
more crops grown alternately along the contour. Usually, each alternate strip
is biennial or perennial so that only alternate strips at only one time. Thus,
any erosion that starts on the bare strip is checked by the crop on the next
prime objective of multiple cropping is to increase the produce from the land,
this practice also protects the soil from erosion. The method involves either
sequential cropping or growing two or more crops on the same piece of land at
the same time. Many schemes involve a mixture of the two.
which is nothing but the covering of the soil with crop residues such as straw,
maize stalks, palm fronds or standing stubble, protects the soil from raindrop
impact and reduces the velocity of runoff and wind. From the conservation
viewpoint, mulch simulates the effects of a plant cover. It is most useful as
an alternative to cover crops in dry areas where insufficient rain prevents the
establishment of a ground cover before the onset of heavy rain or strong winds
or where a cover crop competes for moisture with the main crop.
tropical areas, the side effects of mulch in the form of lower soil
temperatures and increased soil moisture are beneficial and may increase the
yields of coffee, banana and cocoa. Elsewhere the effects of mulching can be
and composition of a soil can be changed in order to render it fit for certain
crops. Good agriculture replaces what it takes from the soil. The most obvious
and natural means is by restoring to the land in the shape of excreta, just
that the soil has given to men and animals. However, the deficiency has to the
made good by artificial fertilizers. Making deep gullies, draining and liming
may also help the soil retain