Soil erosion, demunition of forest and desertification result from land-clearance and over-harvesting. State and explain the undesirable effects of certain agricultural practices on the ecosystem.

Soil erosion is one form of soil degradation by which the topsoil is removed naturally by the wearing actions of rain and wind. It is one of the major environmental problems faced by people today, which reduces agricultural and forestry production significantly and also degrades the quality of aquatic ecosystems.

Cause of soil erosion

Usually soil erosion happen after intensive ploughing and over-grazing, the former with the use of inappropriate machinery can damage soil structure. The soil will easily get loosening and large soil particles are broken down. Large amount of powdery materials is formed. When they mixed with rain water, they will form mud and seal the soil surface. Therefore rain water cannot pass through the soil easily. Ploughing also provides extra air and warmth. This speeds up the rate of bacterial deterioration. Humus, which helps to hold water, is lost at a fast rate, and these further speeds up soil erosion. The latter will increase the rate of consumption of grass that is usually faster than the rate of recovery. Finally, the grass will become too short or die off and the soil will expose to the air. After long time of denudation and weathering, the soil becomes dry, infertile loose, and soil erosion is speeded up.

Soil erosion will seriously affect the stability, structure and texture of soil. When the humus on the top is removed, many vital nutrients are lost. The fertility of soil will decrease, leading to a reduced crop production and introduction of inorganic fertilizer which will bring tons of other environmental problems. No more crops can be cultivated and the farmland maybe be abandoned and even become desert eventually.

Desertification is a process whereby productive farmlands in arid, semi-arid and dry sub-humid areas are degraded into deserts.

Cause of desertification

1. Uncontrolled use of fire for regenerating pasture, for hunting or for agricultural clearing;

2. Over-exploitation of woody resources, particularly for fuel wood and timber;

3. Over-grazing of selective vegetation, e.g. Shrubs, herbs and grasses;

4. Removal of hedges, which can act as wind breaks, on soil so that the soil is more susceptible to erosion by wind;

5. Over harvesting which results in abandoned fields;

6. Monoculture of cash crops, leading to a severe reduction in soil fertility.

Soil erosion is actually a process of desertification. It usually involves the removal of nutrient-rich topsoil, leaving coarse, sandy particles with poor water-retaining ability. As a result, for those lands where are not suitable for plants to grow will finally turn into a desert.

Desertification will decrease the area of farmlands, and significantly threatens the living standard and well-being of people inhabiting the areas concerned. This also leads to social problems such as environmental refugees whose lands are eroded for cultivation or rearing livestock. It also has serious impact on the natural environment. It breaks down the fragile balance that allows plant and animal life to develop in arid, semi-arid and dry sub-humid zones. This breakdown of the equilibrium represents the start of a process which destroys the natural and stable ecosystem.

Deforestation refers to the clearance of forests and the conversion of them for non-forest uses, including agriculture, animal grazing, timbering, and urbanization. Forests may also be destroyed by natural means such as forest fires. The forests can often recover gradually after forest fires. However, deforestation due to human activities tends to be permanent.

Cause of deforestation

1. Animal grazing
Deforestation provides space for livestock and for the growth of grass which is used to feed on the livestock such as sheep and cattle.

2. Agriculture
In many developing countries, farmers cut down trees for growing crops. They cultivate by the combination of shifting culture and slash-and-burn agriculture. The woods are then piled up and burnt, and crops are grown in such ash areas. After few year, the soil becomes in fertile and they will clear another new land.

Forests play a important part in the biosphere. They act as a climatic buffer by retaining moisture in the air, cooling down the air, and maintaining the balance of carbon dioxide level in the atmosphere. They lock up nutrients and maintain their availability to other organisms. They hold the soil and retain rain water. These help to prevent soil erosion, flooding, sedimentation and water pollution. Forests are also important as the habitats for a large variety of organisms.

The clearance of forests causes great impact on both the environment and humans. These include loss of nutrients availability, soil erosion, flooding, water pollution, hotter and drier weather conditions, global warming, as well as reduction in biodiversity.