Soil erosion is defined as the removal of the top layer of the soil through various agents like water and wind.
Types of Soil Erosion
There are two main types of soil erosion. These are:
- Soil Erosion Caused by Water: This is the type of erosion in which the top soil is washed and carried away by running water. The types or kinds of soil erosion caused by water include:
- Rill erosion: This is caused by the accumulation and running away of water which carves narrow channels on the soil through which water flows.
- Sheet erosion: This is the removal of a uniform depth of soil over an extensive area by rainfall. It occurs where the land has gentle slope with bare vegetation.
- Gully erosion: This is the localized removal of soil over steep slopes by heavy rainfall, resulting in the cutting of deep groves called gullies. When gullies become deeper and wider, it forms badland.
Areas of Gully Erosion in Nigeria
- South East of Nigeria – Amucha Ihioma (Imo).
- Ohafia and Aba (Abia).
- Agulu (in Anambra).
- Auchi, Benin (Edo-State).
- South West – Ekiti and Ondo.
- North central – Jos (Plateau).
- Soil Erosion Caused by Wind: Wind erosion is the gradual removal of the loose top by wind deflation. It is common in deserts and semi-arid regions.
Areas of Wind Erosion in Nigeria
- North West of Nigeria – Sokoto, Kebbi.
- North East of Nigeria – Bornu, Yobe.
Causes of Soil Erosion
- Deforestation: This is the removal of vegetation thereby allowing erosion to take place.
- Bush burning: This also exposes the soil to erosion.
- Overgrazing: This is the excessive removal of grasses by animals that feed on them thereby, exposing the soil to erosion.
- Cultivation along slope: This speeds up the rate of erosion when ridges are constructed along the slope instead of across the slope.
- Excessive rainfall/wind: This increases the rate of soil erosion.
- Shifting cultivation: This also exposes the soil to erosion.
- Population pressure on land: Continuous cultivation of the land due to high population eventually exposes the soil to erosion.
- Excavation: This is the digging out of soil for building construction or for mining which later can cause soil erosion.
Effects of Soil Erosion
- Soil erosion causes the removal of top fertile soil meant for crop cultivation.
- It leads to the loss of farmlands.
- It can result in loss of lives and properties.
- It leads to the damage of roads and railway lines.
- It leads to the development of badlands.
- Creation of environmental imbalance.
- It can pollute drinking water from rivers and lakes due to deposition of debris.
- Decline in agricultural production.
Control of Soil Erosion
- Afforestation: This is the planting of trees to control erosion.
- Re-afforestation: This is the replanting of trees in areas which do not contain plants before in order to check erosion.
- Controlled grazing: Few animals should be allowed to graze on an area to avoid soil erosion.
- Contour ploughing: This is the making of ridges across the slope to control erosion.
- Cover cropping: This is the planting of legumes to cover the soil so as to prevent erosion.
- Terracing: This is the method of cutting steps on hill sides to reduce the speed of running water down the hill.
- Improved farming methods: The practice of mixed farming, strip cropping and crop rotation helps to control erosion.
- Legislation: These are laws made to combat erosion through soil conservation boards.
- Enlightenment programmes: People should be educated on the effects of soil erosion and on soil conservation measures.
- Shelter belts: This is the planting of trees in form of belts where wind erosion is dominant so as to serve as wind break and reduce wind erosion.
Desert encroachment is the extension or spread of the desert to areas which were originally not deserts before.
- It is common in areas very close to desert e.g. Sahel Regions in Northern Nigeria like Maiduguri, Damaturu, Sokoto, Birnin-Kebbi, etc.
- North- East of Nigeria.
- North-West of Nigeria.
Causes of Desert Encroachment
- Overgrazing: The excessive removal of the grasses by animals leave the soil bare to desert encroachment.
- Changes in climate: Desert encroachment may also occur when there are changes in the climate of a place from partial wet climate to dry one.
- Bush burning: This exposes the soil thereby encouraging desert encroachment.
- High speed of winds: High speed of winds across the desert carries sand and deposits them on the land e.g. harmattan wind.
- Shift in climate belt: The shifting of climatic belt from one place to another may encourage desert encroachment.
- Deforestation: The cutting down of trees can also encourage desert encroachment.
- Prolonged drought: Desert encroachment can also be caused as a result of prolonged drought or weather in an area where there is a long period of time without rainfall.
- Over cultivation: Over cultivation in the desert fringes e.g. (shifting cultivation) can also be responsible for desert encroachment.
Effects of Desert Encroachment
- Desert encroachment can lead to displacement of people and settlements.
- It leads to crop failure or poor yield of crops.
- It could affect serious farming activities.
- It could cause the loss of pasture or livestock.
- It could result in hot and dusty environment.
- It leads to shortage of water for animal and human consumption.
- It can expose the soil to wind erosion.
- It leads to loss of vegetation.
- It leads to climatic changes.
- It leads to loss of agricultural lands.
- It can bring about famine and hunger.
- It can lead to loss of animals and human beings by death.
- It can also lower the water table in the area.
Control of Desert Encroachment
- Afforestation i.e. the planting of trees to reduce the hardship.
- Irrigation scheme could be introduced to encourage the growth of vegetation.
- Conservation of trees, surface and underground water.
- Creation of shelter belts.
- Rotational grazing can reduce desert encroachment.
- The rate of tree felling or deforestation should be strictly controlled.
- The planting of legumes to cover the soil can also reduce desert encroachment.
- Laws should be made against bush burning so as to prevent desert encroachment.
- The use of wood as fuel should be discouraged as the practice encourages deforestation.
- The people in the affected areas should be educated on the danger of desert encroachment and how it can be prevented or controlled.