The Soil Erosion

While the nature takes from 100 to 400 years to build one centimetre of top soil, man can and often does destroy it almost overnight by haphazard land use and improvident husbandry. Irrational methods of cultivation, deforestation, destruction of natural vegetation due to over­grazing by pasturing animals etc., accelerate denudation. Besides, failure of rains, floods, depopulation and loss of cattle caused by famine and pestilence, disturbance caused by war and interference with or change in the natural drainage system have had their deleterious effect on the soil at some time or the other. (a) Irrational Methods of Cultivation (i) Faulty method of cultivation Particularly on the steeper slopes when the virgin land is ploughed and naked soil is exposed to the rain, the loss of fertile soil is enormous. The potato cultiva­tion in the Himalayas and the Nilgiris, where the rows run straight up and down hill, causes an abnormal rapid loss of soil. (ii) Shifting cultivation It is a primitive form of soil utilization. In shifting cultivation, framers grow food only for themselves and their families. In this system of farming a patch of forest is selected. Its tree and bushes are than cut and burnt down on the ground in order to clear room for a field. The ground is then lightly ploughed and seed is sown broadcast and racked into the soil at the first fall of rain. The soil gives rise to a better yield as it is immensely fertile owing to the wood ashes and accumu­lated humus. After two or three years' crop, when the fertility of the soil is seriously reduced, the people again change their land of cultivation. Thus the essential feature of shifting cultiva­tion is the rotation of fields rather than crops. As a result more and more land are exposed to erosion. (iii) Nature of crop grown In India, as it has been noticed the dry crop producing regions (such as millet, maize, potato, tobacco, cotton and even wheat growing region)