In a broad sense, soil degradation can be defined as the decline in soil fertility, when the nutritional status declines and depth of the soil goes down due to erosion and misuse. Soil degradation is the main factor leading to the depleting soil resource base in India. The degree of soil degradation varies from place to place according to the topography, wind velocity and amount of the rainfall.
Causes of Soil Degradation
The destruction of the soil cover is described as soil erosion. The soil forming processes and the erosional processes of running water and wind go on simultaneously. But generally, there is a balance between these two processes. The rate of removal of fine particles from the surface is the same as the rate of addition of particles to the soil layer.
Sometimes, such a balance is disturbed by
natural or human factors, leading to a greater rate of removal of soil. Human activities too are responsible for soil erosion to a great extent. As the human population increases, the
demand on the land also increases. Forest and other natural vegetation is removed for human settlement, for cultivation, for grazing animals and for various other needs.
Main agents of soil erosion are (1) Water, (2) Wind, (3) Waves and (4) Glaciers
- Sheet erosion: It takes place on level lands after a heavy shower and the soil removal is not easily noticeable. But it is harmful since it removes the finer and more fertile top soil.
- Rill Erosion: Heavy water flow cause rill in Land.
- Gully erosion: It is common on steep slopes. Gullies deepen with rainfall, cut the agricultural lands into small fragments and make them unfit for cultivation. A region with a large number of deep gullies or ravines is called a badland topography. Ravines are widespread, in the Chambal basin. Besides this, they are also found in Tamil Nadu and West Bengal. The country is losing about 8,000 hectares of land to ravines every year.
Soil erosion is a serious problem for Indian agriculture and its negative effects are seen in other spheres also. Eroded materials are carried down to rivers and they lower down their carrying capacity, and cause frequent floods and damage to agricultural
Deforestation is one of the major causes of soil erosion. Plants keep soils bound in locks of roots, and thus, prevent erosion. They also add humus to the soil by shedding leaves and twigs. Forests have been denuded practically in most parts of India
but their effect on soil erosion are more in hilly parts of the country.
Waterlogging and Salinity
- A fairly large area of arable land in the irrigated zones of India is becoming saline because of overirrigation. The salt lodged in the lower profiles of the soil comes up to the surface and destroys its fertility.
- Chemical fertilisers in the absence of organic manures are also harmful to the soil. Unless the soil gets enough humus, chemicals harden it and reduce its fertility in the long run. This problem is common in all the command areas of the river valley projects, which were the first beneficiaries of the Green Revolution.
- The presence of calcium carbonate beneath (kankar) the soil will act as impermeable to water and water gets logged as happened in Indira Gandhi canal regions of Rajasthan. If the soil contains salt content, it will spread to the whole land
due to this.
It is a type of cultivation practiced mainly in North-Eastern states of India. It is a type of slash and burn method of cultivation. After reaping the crops, the land (usually the forest) is slashed and burned. The next cultivation will be in another plot and the burned land will let uncultivated for a period.In the early periods, the gap between two cultivations in a land was 10-20 years. Due to population increase and availability of land is reduced, the gap decreased to merely 2-3 years. This has caused major deforestation, environmental pollution, loss of habitat for wild animals etc. The burning of forest results in soil erosion and gradual degradation of soil.
Another way of human activities leading to soil degradation is by overgrazing. The movement of cattle over and over the pastures pulverizes the soil into finer particles due to the pressure applied by their hoofs. During the dry season, when there is not enough fodder available near the fields, cattle are left to graze over the surrounding grasslands. Overgrazing causes the grass to be torn out of the soil , along with the roots, which weakens the soil. The loose soil gets eroded easily when it rains.
Soil degradation due to overgrazing is common in hilly regions.
According to estimates, about half of the total land of India is under some degree of degradation. Every year, India loses millions of tonnes of soil and its nutrients to the agents of its degradation, which adversely affects our national productivity.
So, it is imperative to initiate immediate steps to reclaim and conserve soils.