Apart from pollution, land and soil face many other problems. These are deforestation, erosion, flooding, water logging, salination, desertification and urbanization. If degradation of soil and land continues at current rates, about one third of the farmland may be destroyed by the end of the century.
1. Soil erosion : Removal of top fertile layer of the soil by water, wind, oceanic waves and glaciers is called soil erosion. Erosion of soil by water generally occur near hills, where high speed rivulets and flooding removes top soil. India experience floods almost every year due to destruction of forests in catchment areas of rivers. Strong winds also erode the soil and bring sand from deserts to adjacent fertile land, converting the latter into desert. Thar Desert in Rajasthan once a fertile land has been formed by shifting of sand from Gujarat Coast.
Erosion occurs in both wet and arid regions, irrespective of whether it is traditional or modernized agriculture. Various human activities such as felling of trees, over-grazing, over cropping and improper tilling accelerate soil erosion. The roots of grasses keep the soil intact. Disruption of the grass cover by plough loosens the soil and makes it vulnerable to erosion. Tilling or grazing on slopes or semi-arid soils increases the rate of soil erosion.
Soil erosion is world-wide phenomenon but it is especially high in Nepal, India, China, Australia, Spain, USSR, USA and Central Africa. Over 40,000 hectares of land are affected by wind and water erosion in India every year.- The damage of top soil in India is 18.5 percent, which is the maximum of the global loss. It is due to over-grazing of live-stocks whose population is largest in India.
2. Shifting cultivation: It is a peculiar practice of slash and burn agriculture prevalent in many tribal communities inhabiting in tropical and sub-tropical regions of Asia, Africa and Oceania (Islands of Pacific Ocean and nearby sea), It consists of cutting down trees and setting them on fire and raising crops on the resulting ash. This practice is called Jhuming in north-eastern India and is spread in 3 x 10 Km2 of tropical or Jhum forests. It is not harmful, if the Jhuming cycles are longer. However, when Jhuming is done in 5 to 10 years of cycle, destroy forests and destabilises the soil
3.Desertification: Transformation of fertile and into a desert by natural or man’s activities is called desertification. It can result from various causes such as erosion of top soil, shifting of sand dunes by wind and overcrazing in lands sparsely covered by grass. Many deserts of the world have developed by the aforesaid human activities.
4. Developmental activities : Various developmental activities such as rapid urbanization, construction of dams, roads, railways, airports, Industries and mining have caused excessive loss of large areas of fertile and productive croplands, woodlands and grasslands.
Control of Land Degradation
The following measures can be adopted to check the land degradation:
(1) Land degradation by soil erosion, floods and water logging can be checked by restoring forests and grass covers.
(2) Degradation of soil by shifting cultivation can be prevented by crop rotation, mixed cropping and plantation cropping. These practices would Improve soil fertility.
(3) Salinity of soil can be checked by improving drainage, salinated lands can be reclaimed by leaching them with more water, if the ground water table is not high.
(4) Advancement of deserts can be checked by mulching (use of artificial protective covering) or by growing appropriate plant species and by raising trees as wind breaks.