Soil Erosion | Geography Optional for UPSC (Notes) PDF Download

Erosion is a natural process that involves the detachment and removal of loosened rock materials and soils by external forces, without human interference. This is also known as geological erosion. The slow removal of soil is an inevitable and universal part of the natural geological process of denudation.

• However, accelerated erosion refers to the increased rate of erosion caused by human-induced changes in land use. This type of erosion is usually called man-induced erosion or soil erosion. Soil erosion refers to the loosening and displacement of topsoil particles from the land. It can occur as a slow, natural process (geological erosion) or as a fast process that is exacerbated by human activities such as deforestation, floods, and tornadoes.
• Soil erosion is a severe form of soil degradation in which the natural geomorphological process is accelerated, causing soil to be removed at a rate that is ten to several thousand times faster than under natural vegetation conditions. This rapid removal occurs much faster than the rate at which new soil forms.
• Accelerated soil erosion or man-induced soil erosion primarily occurs in humid climate regions where humans have extensively cleared forests, removed grasslands, and allowed overgrazing and trampling by livestock at an alarming rate.

Soil erosion involves two main processes:

1. Loosening and detachment of soil particles from the soil mass, and
2. Removal and transport of the detached soil particles downslope.

Human activities have significantly modified and changed land use patterns, leading to increased soil erosion. It is essential to understand and manage these changes to prevent further degradation of the land and maintain soil health.

L.D. Meyer and W.H. Wischmeier emphasized that the ease with which soil particles can be detached from the soil mass is a critical factor in soil erosion. This detachability is largely influenced by the grain size, or the size and cohesiveness of the particles. When soil particles have a grain size larger than 0.2 mm, a greater force from the velocity of moving water is required to detach them. As the grain size increases beyond 0.20 mm, the critical velocity needed for detachment also increases.

• Morisawa (1968) identified two primary independent factors that determine the rate and kind of soil erosion that occurs on hill slopes: climate and geology.
• Soil erosion and land degradation are significant issues that disrupt the global ecological balance. The rapid growth of the human population has put immense pressure on land and soil resources, leading to land degradation and increased soil erosion. Globally, over 4.85 billion acres (1.96 billion hectares) or 17% of the Earth's vegetated surface has been negatively affected by human activity to varying degrees.

Types of Soil Erosion

1. Water erosion
2. Wind erosion

1. Water erosion
Running water is one of the main agents, which carries away soil particles. Soil erosion by water occurs by means of raindrops, waves, or ice. Soil erosion by water is termed differently according to the intensity and nature of erosion.

• Raindrop erosion 
• Sheet erosion 
• Rill erosion
• Steam banks erosion
• Erosion due to landslides
• Coastal erosion.

(i) Raindrop erosion

• Raindrops behave like tiny bombs when falling on exposed soil, displace soil particles and destroy soil structure.
• Average size of a raindrop is approximately 5 mm in diameter falling through the air hits the soil at a velocity of 32 km/hr.
• Presence of vegetation on land prevents raindrops from falling directly on the soil thus erosion of soil in areas covered by vegetation is prevented.

Sheet erosion

• The detachment and transportation of soil particles by flowing rainwater is called sheet or wash off erosion.
• This is a very slow process and often remain unnoticed.

Rill erosion

• In rill erosion finger like rills appear on the cultivated land after it has undergone sheet erosion.
• These rills are usually smoothened out every year while forming.
• Each year the rills slowly increase in number become wider and deeper.
• When rills increase in size, they are called gullies. Ravines are deep gullies.

Streambank erosion

• The erosion of soil from the banks (shores) of the streams or rivers due to the flowing water is called bank erosion.

Landslide

• A sudden mass movement of soil is called a landslide. Landslides occur due to instability or loss of balance of land mass with respect to gravity.

Coastal erosion

• Coastal erosion of soil occurs along seashores. It is caused by the wave action of the sea and the inward movement of the sea into the land.

Consequences of water erosion

• Water erosion leads to the loss of the most fertile layer of soil, leaving behind the less fertile subsoil. This occurs as the fine particles in the topsoil, which contain the majority of nutrients and organic matter required by plants, are removed. As a result, the soil's capacity to store water is reduced.
• The removal of seeds and seedlings due to erosion causes the soil to become bare, making it more susceptible to further erosion by both wind and water. Additionally, the loss of seeds and seedlings lowers the soil's ability to retain water.
• Different types of water erosion, such as sheet, rill, gully, and stream bank erosion, contribute to the siltation of rivers, streams, and agricultural fields. This deposition of silt can damage crops and pastures, as well as lead to the sedimentation of water bodies like streams, dams, and reservoirs.
• The sedimentation of water bodies negatively impacts water quality and can harm aquatic habitats and organisms. Furthermore, coastal erosion can result in the surrounding land being covered by sand, causing further damage to the environment.

2. Wind erosion
Wind-induced soil erosion primarily occurs in regions where natural vegetation has been depleted. These circumstances are typically found in arid and dry zones near the sandy coastlines of oceans, lakes, and rivers.
There are three primary methods by which soil particles are dislodged and moved by wind:

• Siltation: This process involves the soil being lifted and carried by the wind in a series of brief, bouncing movements.
• Suspension: In this case, soil particles are suspended in the air and transported over long distances, often by strong winds.
• Surface creep: This phenomenon occurs when soil particles are pushed along the ground by forceful, high-velocity winds.

Consequences of wind erosion

• Wind erosion leads to the removal of finer soil components such as organic matter, clay, and silt in a colloidal form, leaving behind coarser and less fertile materials. This results in a decline in the soil's productive capacity, as the majority of plant nutrients are attached to the smaller colloidal soil particles that get eroded away. 
• Moreover, wind erosion can cause significant damage to roads and productive agricultural lands by depositing vast amounts of airborne soil particles onto these surfaces.

Soil Erosion caused by Human Activity
Certain human activities accelerate soil erosion.

• Deforestation
• Farming
• Mining
• Developmental work, human settlements, and transport

Deforestation is the process of cutting down and removing trees, clearing away forest debris, as well as the destruction caused by livestock grazing, trampling, and forest fires. This activity leads to soil erosion and land degradation, as it disrupts the vital balance between soil and plant nutrients.

Agriculture is another significant human activity that contributes to soil erosion. As crops are grown, harvested, and land is plowed repeatedly, the soil is exposed to wind and rain, preventing it from retaining moisture. This agricultural process results in severe soil erosion on farmland, known as wash off or sheet erosion. In arid and semi-arid regions, wind-driven sand movements have a similar impact as sheet erosion, where water is the primary factor. As a result, a gradual process of desertification occurs, leading to a continuous loss of land fertility.

The following agricultural practices can lead to accelerated soil erosion

• Tilling or ploughing: These practices disturb the natural soil surface and protective vegetation, increasing the chances of erosion.
• Continuous cropping: Repeatedly growing crops on the same land and expanding cultivation to marginal and sub-marginal lands can encourage soil erosion.
• Cultivation on mountain slopes: Farming on sloping lands without proper land treatment measures, such as bounding, terracing, and trenching, can lead to soil erosion and loss of nutrients.
• Monoculture: This refers to planting only one type of crop in a field. Monoculture can contribute to soil erosion in several ways:
  • Harvesting a monoculture crop all at once leaves the entire field bare and exposed to wind and water erosion.
  • Without vegetation to retain it, natural rainfall runs off the surface rather than being absorbed by the soil, carrying away topsoil and causing erosion and degradation.
  • If a disease or pest infestation occurs, the entire crop may be destroyed, leaving the soil vulnerable to wind and water erosion.
• Overgrazing: Allowing too many animals to graze on a grassland can lead to trampling and destruction of vegetation. Without adequate plant cover, the land becomes highly susceptible to both wind and water erosion.
• Economic activities: Extracting natural resources such as metals, minerals, and fossil fuels can disturb the land, leading to soil erosion and significant changes in the landscape.
• Developmental activities: Soil erosion can also occur due to development activities like housing, transportation, communication, and recreation. Construction of houses, roads, and rail tracks can cause accelerated soil erosion and disrupt the natural drainage system by disturbing the land.

Consequences of Soil Erosion

• Soil erosion has numerous consequences for the environment, agriculture, and human activities. The loss of topsoil, which contains the majority of nutrients and organic matter necessary for plant growth, is one of the main issues. Wind erosion specifically removes finer soil materials such as organic matter, clay, and silt, leaving behind coarser and less fertile soil.
• Another consequence of soil erosion is the removal of seeds and seedlings, which leads to bare soil. This makes the soil more susceptible to further erosion by both wind and water. Additionally, the loss of seeds and seedlings reduces the soil's capacity to retain water.
• Erosion in the form of sheet, rill, gully, and stream bank erosion contributes to the sedimentation of rivers, streams, and fields. This results in crop damage, pasture destruction, and sediment buildup in water bodies such as streams, dams, and reservoirs. This sedimentation can cause deterioration in water quality and harm aquatic habitats and organisms.
• Gully erosion can lead to significant soil loss, with some gullies reaching up to 30 meters in depth. This can severely limit land use and disrupt normal farming operations. Streambank erosion, on the other hand, not only results in land loss but can also change the course of rivers and streams. This type of erosion can also damage public roads and infrastructure.
• Wind erosion can have detrimental effects on roads and agricultural fields by depositing large amounts of airborne soil particles. This can lead to reduced fertility and productivity of the land.
• Landslides, or the mass movement of land, can also hinder agricultural production and limit land use. These events can result in the loss of life for both humans and animals.
• Finally, coastal erosion can lead to the encroachment of sand onto adjacent land areas, impacting the overall landscape and land use. Overall, soil erosion has wide-ranging consequences that can significantly affect the environment, agriculture, and human activities.

Prevention of Soil Erosion

• To prevent soil erosion, it is crucial to maintain a vegetation cover that prevents soil exposure to rain. Vegetation is essential because plant roots help hold soil particles together, and plants can also intercept rainfall, shielding the soil from the direct impact of raindrops.
• Controlling cattle grazing is another important measure to prevent soil erosion. Additionally, adopting crop rotation and leaving the land fallow (i.e., not planting anything in the soil for a certain period) can help preserve soil quality.
• Improving vegetation and soil management to increase soil organic matter is also beneficial for preventing erosion. To reduce stream bank erosion, it is necessary to store runoff water in catchment areas for as long as possible, which can be achieved by maintaining vegetation cover and constructing dams for water storage.
• To prevent or reduce coastal erosion, it is essential to re-establish protective vegetation along the beaches. The most effective method of controlling coastal dune erosion is to avoid disturbing the dunes and the coastal system. Furthermore, building construction and other developments should be situated behind the dune systems.
• For sandy soils, it is important to maintain a vegetation cover of at least 30%. Wind access to the soil should be controlled by leaving stubble or mulch on the soil (stubble refers to the remnants of a crop left after harvesting). Planting trees in the form of a shelter belt can also help break or control wind speed, further preventing soil erosion.

Land/Soil Degradation
Degraded land is classified on the basis of the productive capacity of the land. Slight degradation refers to the condition where crop yield potential is reduced by 10%. Moderate degradation refers to 10-50% reduction in yield potential and in severe degradation means that the land has yield potential is lost more than 50% of its potential yield capacity (productive capacity).

Some causes of land degradation are

• Use of agrochemical (chemical fertilizers and pesticides)
• Excessive irrigation
• Cultivation of high yielding plant varieties.

Agrochemical and their harmful effects on land

Agrochemicals are applied to the soil for two main reasons namely to:

• replenish or replace soil nutrients by using chemical fertilizers.
• Destroy plant pests by using toxic chemicals called pesticides.

(i) The adverse effect of use of chemical fertilizer:
Plants take up nutrients from the soil. Repeated crop cultivation depletes nutrients in the soil. Therefore, nutrients in soil have to be augmented periodically by applying chemical fertilizers. However, excess use of chemical fertilizers and pesticides leads to the following problems:

• Most of the chemical fertilizers used in modern agriculture contain macronutrients like nitrogen, phosphorus, and potassium (NPK). The excessive addition of NPK to the soil however causes the plants to absorb more micronutrients from the soil. As a result, the soil becomes deficient in micronutrients like zinc, iron, copper, etc, and the soil productivity decreases.
• Fertilizer which is not used by plants is washed down with rainwater and carried into water bodies, resulting in eutrophication or algal bloom leading to the death of aquatic life.
• About one-fourth of the applied fertilizer is not used by the crop plants and is leached down into the soil and underground water aquifer. Excess nitrates in water are harmful especially in bottle-fed infants who cause the disease, methemoglobinemia.

(ii) The adverse effects of the use of plant protection chemicals
Toxic chemicals used to kill pests of cultivated crops. These poisonous chemicals are collectively called biocides (agents that kill organisms) they are not selective i.e., they not only kill the target pests but may also kill other non/not target and other useful organisms. Moreover, Biocides tend to remain active long after destroying the target organisms i.e. pests, weeds, fungi or rodents. It is persistence that makes these chemicals harmful to us.

Problems due to excessive irrigation
Excessive irrigation of soil may leads to waterlogging and accumulation of salt in the soil. Both these degrade the soil.

• Waterlogging: Excessive irrigation of land without proper drainage raises the water table. This causes the soil to become drenched with water or waterlogged. This waterlogged soil cannot support good plant growth due to a lack of air particularly oxygen in the soil, which is essential for the respiration of plant roots. Waterlogged soils lack mechanical strength and cannot support the weight of plants that fell down and get logged thus become submerged in the mud.
• 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 leftover salt accumulated 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.

Impact of high yielding plant varieties on leads to soil degradation
High Yielding Varieties (HYV) have played a significant role in boosting food production, but they have also had considerable effects on the environment. HYVs are artificially developed varieties of agricultural crops, fodder plants, forest trees, livestock, and fish. These varieties necessitate sufficient irrigation and the extensive application of fertilizers and pesticides to achieve their full potential. However, the use of such agrochemicals has contributed to land degradation, which is an alarming environmental concern.

Measures for Preventing Soil Erosion and Land Degradation

• Planting trees: Planting trees helps in preventing wind erosion by breaking the force of the wind. Trees not only protect the soil from the sun, wind, and water, but also help in holding the soil particles together.
• Implementing cultivation and farming techniques: There are various cultivation and farming techniques that can help reduce soil erosion: Cultivating land perpendicular to the wind direction can help minimize wind erosion.
  • Ploughing style: Certain ploughing styles, such as contour ploughing or ploughing at right angles to the slope, can significantly reduce soil erosion. The ridges created during this process act as small barriers that help water seep into the soil rather than flow down the slopes, causing erosion. Contour ploughing can decrease soil erosion by up to 50%.
  • Strip farming: This technique involves planting the main crops in wide rows and filling in the gaps with another crop to ensure complete ground coverage. This helps in slowing down water flow and allowing it to soak into the soil, reducing erosion problems.
  • Terracing: This method involves creating terraces on steep slopes to prevent water flow and reduce soil erosion. However, terraces may require significant maintenance and repair due to their susceptibility to erosion.
  • Timing of tillage: The season in which a field is tilled can greatly affect the amount of erosion that occurs during the year. For example, if a field is ploughed in the fall, erosion can happen all winter long, whereas if the ground cover remains until spring, there is less time for erosion to occur.
  • No-till cultivation: This method involves using specialized machinery to loosen the soil, plant seeds, and manage weed control with minimal disturbance to the soil. However, this practice can lead to increased weed and insect populations, which can compete with or damage crops.
  • Polyvarietal cultivation: This technique involves planting several varieties of the same crop in a field. As the harvest time varies for different crop varieties, they can be selectively harvested at different times, ensuring that the entire field is not exposed at once, thus protecting the land from erosion.
  • Adding organic matter to the soil: Incorporating organic matter into the soil, such as crop residues or entire crops grown specifically for ploughing into the ground, can help reduce soil erosion. Soil microbes decompose the organic matter and produce polysaccharides, which are sticky substances that help bind soil particles together and make the soil more resistant to erosion.
    
    Terrance Farming

Agriculture technologies for preventing soil degradation

• Organic farming and green manures: Rather than using chemical fertilizers to increase the nitrogen content in the soil, a more natural approach can be adopted by utilizing nitrogen-fixing bacteria found in the root nodules of legumes. Additionally, employing organic fertilizers such as cow dung and agricultural waste can enhance the nutrient levels in the soil. This helps to decrease the extended use of chemical fertilizers and minimize their harmful effects.
• Biofertilizers: Microorganisms are crucial components of nutrient-rich soils. They contribute to the development of soil structure, increase the availability of essential nutrients, and enhance the soil's physical properties. A wide variety of microorganisms can be used as biofertilizers to improve the nutrient status of agricultural fields.
• Biological pest control: Natural predators and parasites of pests play a significant role in managing plant pests and pathogens. Farmers are increasingly using these biological control agents to control or eradicate plant pests. As these agents do not enter the food chain or poison animals, they are less likely to harm humans.

Conclusion

Frequently Asked Questions (FAQs) of Soil Erosion

What is the difference between geological erosion and accelerated soil erosion?

Geological erosion is a natural process that involves the detachment and removal of loosened rock materials and soils by external forces, without human interference. Accelerated soil erosion, on the other hand, refers to the increased rate of erosion caused by human-induced changes in land use, such as deforestation, agriculture, and construction activities.

What are the primary types of soil erosion?

There are two main types of soil erosion: water erosion and wind erosion. Water erosion can occur in various forms, such as raindrop erosion, sheet erosion, rill erosion, streambank erosion, and coastal erosion. Wind erosion primarily occurs in regions where natural vegetation has been depleted, leading to the displacement of soil particles by wind.

How do human activities contribute to soil erosion and land degradation?

Human activities such as deforestation, agriculture, mining, and developmental work can lead to increased soil erosion and land degradation. These activities can disrupt the natural balance between soil and plant nutrients, expose soil to wind and water, and result in the loss of fertile topsoil.

What are some consequences of soil erosion?

Soil erosion can lead to a decline in soil fertility and productivity, loss of seeds and seedlings, sedimentation of water bodies, damage to crops and pastures, and deterioration of water quality. It can also negatively impact aquatic habitats and organisms, disrupt the landscape, and limit land use.

What are some measures that can be taken to prevent soil erosion and land degradation?

Measures to prevent soil erosion and land degradation include planting trees, implementing cultivation and farming techniques such as contour ploughing, strip farming, and no-till cultivation, adding organic matter to the soil, and adopting agriculture technologies like organic farming, green manures, biofertilizers, and biological pest control.