Checking Soil Erosion

Checking Soil Erosion

Khilendra Basnyat

In modern 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.

Soil erosion 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.

Soil erosion has caused unfair impact in Canada and has reached serious dimensions in Venezuela, Brazil, Uruguay and Argentina.

In Africa, marginal land has been destroyed by over cultivation and overgrazing of grasslands.

In Australia, the government has come to take a serious thought of the problem and is prompt to restrict its ravages.

In some 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.

The rampant 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.

The 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.

Soil erosion 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.

Another form 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 strip.

Although the 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.

Mulching, 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.

In semi-humid 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 detrimental

The texture 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