Soil Erosion
It has already been stated that the formation of soil, as it exists today, has taken centuries (see sec. 8.2). The top soil is the most important as all agricultural activities depend on it.
The upper most layer of the soil is a vital component since all the nutrients required by plant are present in this layer. At times, if it so happens that the top soil is dissipated or taken to other places by water or wind, then this situation is referred to as ‘soil erosion’. The soil which has been eroded becomes unfit or unsuitable for vegetation or agricultural production. It has been found that on global scale, the fertile land is lost by erosion at the rate of about ten million hectares per year.9.4.1 Causes of Soil Erosion
Soil erosion is a natural process and is caused by the flow of water over the fields and by wind. Following factors influence the rate of soil erosion.
(1) Deforestation and loss of vegetation cover increase the rate of erosion.
(2) Cultivation on slopes of mountains increase the rate of erosion.
(3) Soils with fine texture and low organic content are more susceptible to erosion.
9.4.2 Effects of Soil Erosion
Soil erosion depletes the inorganic nutrients like nitrogen, phosphorus, potassium and calcium present in soil. It also uproots the organisms living in the soil - this results in the loss of organic nutrients. The soil erosion also leads to Ihereductioninsoilproductivity.
9.4.3 Control of Soil Erosion
Formation of soil is an extremely slow process and it takes 200 - IOOO years to form one inch of topsoil. In view of this, it is very necessary to conserve the soil and prevent its erosion. Following are some important methods of ControlUng soil erosion.
(i) Rotation of crops: This procedure ensures that some part of the land is continually covered by vegetation.
(ii) Tfflage at right angle to the slope of land: This is known as contour farming. This procedure creates a series of ridges that slow down the flow of water and thus prevent the soil erosion. This method is useful on gentle slopes.
(iii) Strip Farming: This is used on steep slopes. The procedure involves alternating strips of closely sown crops. Alternative bands of wheat and soya beans are commonly sown. The closeness of the strips retards the flow of water and so prevents soil erosion.
(iv) Using wind brakes: It is the practice of planting trees or other plants that protect the bare soil from the full force of winds. Wind brakes decrease the speed of wind and hence reduce the quantity of soil that the wind can carry away. Thus, soil erosion by wind is reduced.
9.5