Land degradation and preventive measures

What is Land Degradation?

Land Degradation can be termed as the degradation of the quality of land resulting in the reduction of fertility and crop production capacity of the land. Degraded land is classified on the basis of its productive capacity and is divided into slight, moderate and severe degradation.

When a land slightly degrades, its crop yielding potential is reduced by 10 per cent. When the yielding capacity decreases by 10-50 per cent, the land is supposed to be moderately degraded and with severe degradation, the yielding potential of the land reduces by more than 50 per cent. There are numerous causes of land degradation. The following are some major factors

Use of agrochemicals

Agrochemicals are used on the soil to replenish or replace soil nutrients by using chemical fertilisers and to destroy plant pests by using pesticides. Chemical fertilisers have adverse effects on the soil. Since plants gather their nutrients from soil, repeated crop cultivation depletes the soil of the essential nutrients. Therefore, nutrients in the soil have to be augmented periodically with chemical fertilizers. However, excess use of chemical fertilizers and pesticides leads to the following problems:

Widespread imbalance in the soil nutrients: Most of the chemical fertilizers used in modern agriculture contain macronutrients like nitrogen, phosphorus and potassium (NPK). Excessive addition of NPK to the soil, however, causes plants to absorb more micronutrients from the soil. As a result, the soil becomes deficient in micronutrients like zinc, iron, copper etc, and its productivity decreases.

Eutrophication of water bodies: The fertilizer not used by plants is washed down with rainwater and carried into water bodies, resulting in eutrophication or algal bloom leading to death of aquatic life.

Health problems: About one fourth of the applied fertilizer is not used by the crop and instead is leached down into the soil and underground water aquifer. The chemical that usually leaches down is nitrate whose increased concentration in drinking water may cause serious health problems. Excess nitrates in water are harmful, especially to bottle-fed infants who contract the disease methaemoglobinaemia.

Plant protection chemicals like- pesticides, herbicides, insecticides fungicides, rodenticides are toxic in nature and are generally used to kill insects, weeds, fungi and rodents in order to protect crop plants from their attack. These poisonous chemicals are collectively called biocides (agents that kill organism). They are not selective i.e. they not only kill target pests but also other useful organisms. Moreover, Biocides tend to remain active long after destroying the target organisms i.e. pests, weeds, fungi or rodents. Its persistent nature is what makes these chemicals harmful.

Continued application of biocides causes various problems:

1. Contamination of food materials and drinking water

2. Disruption of balance of the natural ecosystem

3. Gradual increase in the immunity of pests: Biocides after a period of time become ineffective on the pest, leading to excessive multiplication of the pests. 4. Most of these chemicals are persistent and are non-biodegradable. They persist in the plant or animal body once they enter the food chain. Their concentration in the organisms multiplies progressively through the food chain due to biological magnification.

Excessive irrigation:

Excessive irrigation of soil may leads to water logging and accumulation of salt in the soil. Both these degrade the soil.

Water logging: Excessive irrigation of land without proper drainage raises the water table. This causes the soil to become drenched with water and become water logged. The soil thus cannot support good plant growth due to lack of air particularly oxygen in the soil, which is essential for respiration of plant roots.

Salt affectation: In areas of high temperature, excessive irrigation of land usually causes the accumulation of salt in the soil. This is because water evaporates fast leaving behind traces of salt in the soil. As cycles of irrigation are repeated, the left over salt accumulates and forms a thick layer of grey or white effervescence on the surface. The productivity of salt affected soil is low . Plants in saline soil are unable to absorb nutrients and so face water stress (lack of water) even when moisture is abundant in the soil.

High yielding plant varieties:

High yielding plant varieties have helped increase food production but at the same time have also greatly impacted the environment. The HYVs require adequate irrigation and extensive use of fertilizers, pesticides to be successful.

Land degradation can be prevented by following practices

Organic farming or green manures

Organic farming is an agricultural technique where the land is supplemented with organic fertilisers instead of chemical ones. Legume root nodules are the best source for nitrogen and natural fertilisers such as cow dung, agricultural wastes also improve nutrients value of the soils.

Bio fertilisers

Micro-organisms are important constituents of fertile soils. They participate in the development of soil structure, add to the available nutritional elements and improve the physical conditions of soil. A large variety of micro-organisms are used as bio-fertilisers for improving the nutritional status of crop fields.

Biological pest control

The natural predators and parasites of pests play a significant role in controlling plant pests and pathogens. There are more than 15,000 naturally occurring microorganisms which can be potentially used as biological pesticide.

Measures for preventing land degradation

Trees hold the soil together so it cannot be scattered by wind or washed away by the water. Hence, the soil nutrients are locked in the land. Cultivation of land at the right angles to the direction of wind helps reduce soil erosion by wind. Tilling the field at right angles to the slope is called counter ploughing and helps prevent or reduce soil erosion. The ridges created act as tiny dams that hold water and help seepage into the soil instead of letting it run down the slopes causing soil pollution. Contour ploughing can reduce soil erosion by upto 50 per cent.

Strip farming is another method to prevent soil erosion. It involves planting the main crops in widely spaced rows and filling in the spaces with another crop to ensure complete ground cover. The ground is completely covered so it restricts water flow which thus soaks down into the soil, consequently reducing erosion problems. Terracing is mostly practiced on the slopes. In this method, terraces are created on the steep slopes. This is another way of preparing fields for plantion and prevention of soil erosion. There are disadvantages of terracing however, in that the terraces themselves can be easily eroded and they generally require a lot of maintenance and repair.

The time or season at which a field is tilled can also have a major effect on the amount of erosion that takes place during the year. If a field is ploughed in the fall, erosion can take place all winter long, however if the ground cover remains until spring, there is not as much of a time for erosion to take place. While No-till cultivation is also used as a preventive method for soil erosion. Specialised machinery are available that can loosen the soil, plant seeds and take care of weed control all at once with minimum disturbance to the soil.

Polyvarietal cultivation also helps in controlling soil erosion. In this method the field is planted with several varieties of the same crop. As the harvest time vary for different varieties of the crops they are selectively harvested at different time. As the entire field is not harvested at one time and so it is not bare or exposed all at once and the land remains protected from erosion.