Soil erosion is a major problem in agriculture. Tonnes of soil is lost from the field every year, this not only reduces production but also the eroded soil acts as pollutants to rivers, lakes and other water systems.
Soil is the top layer of the earth’s surface that is capable of sustaining life. Therefore it is very important to farmers who depend on it to provide abundant, healthy crops each year.
One major problem in agriculture is soil erosion, which is the deterioration or the detachment of soil particles from one place to another by the action of a different medium in a given site. Wind, water, ice, animals and the use of tools by man are usually the main causes of it.
Erosion is a natural process that usually does not cause any major problems. It becomes problematic when anthropogenic activities are much faster than under normal conditions.
Worldwide farmers are losing an estimated 24 billion tonnes of topsoil every year. Topsoil contains most of the soil nutrients, organic matter and pesticides which are necessary for crop cultivation. Soil erosion causes these substances to move also. Therefore fertilizers and organic matter must be added in an attempt to restore the soil to its original composition.
Location of Soil Erosion
The severity may vary from place to place. Wind and water are the main sources. The plant cover and size of soil particles are two main factors that are associated with soil erosion. Wind erosion is a more common problem in dry, windy regions with smooth flat terrain. Water erosion is a problem in wet regions with slopy hilly terrain.
Soil erosion is caused by natural processes as well as human activities. The natural processes can be divided into:
Geological soil erosion is a natural process that tends to bring the earth’s surface to a uniform level. This erosion occurs continuously and at a slow rate. it is mainly caused by rainfall, runoff, slopes, wind velocity and gravitational force. This erosion is also called natural erosion. In this erosion, soil development is more than soil erosion.
Under cultivation, the land experiences a lot of pressure from outside and consequently the balance between vegetation cover and the climate is disturbed. Thus, removal of surface water by natural agencies takes place at a faster rate than it could be built up by soil-forming process.
Erosion occurring during these periods can be referred to as accelerated erosion. its rate and magnitude are higher than those in normal geological erosion.
There are mainly two types of soil erosion:
1. Water erosion Removal of topsoil by water is called water erosion. it takes place in the following ways:
- Splash Erosion: It is caused by the beating action of raindrops. This is the first stage of water erosion. In this erosion soil particles detach and disperse due to the force of raindrops.
- Sheet Erosion: The removal of the entire topsoil as a result of heavy rains is called sheet erosion. It is also known as farmers’ death due to the productive layer of the soil. This erosion is mostly occurring in low organic matter content soil and poor vegetative area.
- Rill Erosion: Runoff water moves across the soil-forming small streams. The top is removed only in these rills formed by water streams. These rills can be removed by ploughing.
- Gully Erosion: The advanced stage of Rill erosion is Gully erosion. Deep depressions called the gullies are formed by swiftly moving waters causing soil erosion on them. These gullies cannot be removed by normal tillage operations.
2. Wind Erosion The cause of erosion is wind. it is more in areas where there is less or no vegetation covering the land. The fast-moving wind moves the fine particles to other places. The wind laden with fine sand deposits the latter and forms sand dunes. Shifting sand dunes are common in dry areas.
Major Causes of Soil Erosion
Excessive rainfall: Due to excessive rainfall and poor water holding capacity of the soil, water moves on the surface is called water runoff and it removes top fertile soil.
Human activities: Human activities accelerate the disappearance of the protective cover of natural vegetation and cause soil erosion. It is called artificial erosion.
Over-grazing: Over-grazing leads to the absence of ground vegetation, causes depletion of soil organisms.
Deforestation: It causes soil erosion by rapid rainfall and the flow of wind.
Mining activities: Mining activities such as open cast mining and underground mining leads to soil erosion. Open cast mining helps in the complete removal of soil and leads to the destruction of total land area and loss of productive area. Underground mining leads to the whole area of depression and it becomes a waste of land. it also causes runoff acids which are crude soil. The toxic chemicals from solid wastes are absorbed by soil and may kill plants and animals.
Shifting cultivation: As forests are slashed and burned, it reduces humus content and decreases water-holding capacity of the soil. So cultivators move to another patch of the forest for fresh cultivation. The resulting exposure of the soil to rain and wind causes drastic soil erosion.
Effects of Soil Erosion on Agriculture
- Loss of fertile topsoil
- Loss of rainwater
- Loss of plant nutrients from the soil
- Accumulation of sand and other unproductive coarse materials on productive soil
- Silting of reservoirs, lakes and irrigation channels
- Fragmentation of land mainly by gully erosion
- Increase flooding condition
- Adverse effects on human health crop and yield
- Destroy soil structure and other physical problems
- Loss of biodiversity
Management of Soil Erosion
- Growing cover crops like cowpea which protect direct effects of raindrops
- Addition of organic matter to the soil that binds soil particles and reduces soil erosion
- Afforestation decreases runoff and prevents soil loss
- Levelling of land should be maintained
- Growing of crops across the slopes
- Growing of windbreak and shelterbelts
- Use of agroforestry system
- Avoid fallowing
- Make a gully structure to check water steam like a dam, water spill structure
- Adopt contour cultivation in hilly or sloppy area.