Erosion is a comprehensive natural process involving the detachment and removal of loosened rock materials and soils through exogenetic processes without human interference, also known as geological erosion.
The slow removal of soil is a natural geological part of the denudation process and is both inevitable and universal.
Accelerated erosion refers to an increased rate of erosion due to various land-use changes impacted by human activities, thus "soil erosion" commonly implies accelerated or man-induced erosion.
Causes of World Land Degradation
Soil erosion involves the loosening and displacement of topsoil particles from the land. It may be:
A slow process (geological erosion)
A fast process, accelerated by deforestation, floods, tornadoes, or other human activities
Soil erosion is an extreme form of soil degradation, accelerating the geomorphological process so that soil is removed at a rate many times faster than under natural vegetation conditions, and quicker than new soil formation.
Accelerated soil erosion primarily affects humid climates, where extensive forest clearance, grassland removal, overgrazing, and livestock trampling are practiced.
Soil erosion involves two main processes:
Loosening and detachment of soil particles from the soil mass
Removal and downslope transport of the detached particles, largely influenced by human-modified land-use patterns
L. D. Meyer and W. H. Wischmeier stated that the detachability of soil particles is a crucial factor in erosion. This detachability is dependent on grain size and the cohesiveness of particles.
Particles with a grain size above 0.2 mm require greater force, provided by the velocity of moving water, to detach. The critical velocity needed to detach particles increases with grain size above 0.20 mm.
Morisawa (1968) identified two major independent factors controlling the rate and type of soil erosion on hill slopes: climate and geology.
Soil erosion and land degradation together form one of the major challenges to ecological balance globally. Rapid human population growth has significantly strained land and soil resources, resulting in increased land degradation and soil erosion.
Worldwide, more than 4.85 billion acres (1.96 billion hectares) or 17% of the Earth's vegetated land has been degraded to varying extents due to human activity.
Types of Soil Erosion
Soil erosion is classified based on the physical agent responsible for erosion:
Water erosion
Wind erosion
Water Erosion
Water erosion occurs as soil particles are carried away by:
Raindrops
Running water
Waves or ice
Types of water erosion include:
Raindrop erosion: Raindrops act like tiny bombs, displacing soil particles and damaging soil structure.
Average raindrop: 5 mm in diameter, hitting soil at 32 km/hr.
Vegetation helps prevent soil erosion by absorbing raindrop impact.
Sheet erosion: Slow, unnoticed erosion where soil particles are detached and transported by flowing rainwater.
Rill erosion: Small rills form on cultivated land, growing wider and deeper over time, eventually becoming gullies or ravines.
Streambank erosion: Soil erosion from the banks of rivers or streams due to flowing water.
Landslide erosion: A sudden movement of soil due to instability or loss of balance with respect to gravity.
Coastal erosion: Erosion along seashores due to wave action and the inward movement of the sea.
Consequences of Water Erosion
Loss of the most fertile soil layer, leaving less fertile subsoil.
Removal of fine particles containing nutrients and organic matter.
Seeds and seedlings are often washed away, leaving bare soil prone to further erosion.
Leads to siltation in rivers, streams, and fields, harming aquatic habitats.
Coastal erosion can cover adjoining land with sand, making it less productive.
Wind Erosion
More common in areas where vegetation has been destroyed, especially in arid or dry regions.
Siltation: Soil particles are blown by wind in short bounces.
Suspension: Particles are transported long distances in suspension.
Surface Creep: Particles are moved along the ground by high-velocity winds.
Consequences of Wind Erosion
Removes finer, fertile soil particles, including organic matter, clay, and silt.
Loss of soil productivity as nutrients are carried away in smaller particles.
Wind-deposited soil particles can damage roads and fertile fields.
Soil Erosion Caused by Human Activity
Human activities that accelerate soil erosion include:
Deforestation: Involves cutting trees, removal of forest litter, and livestock browsing. Leads to soil erosion, land degradation, and nutrient loss.
Farming: Agriculture activities, like plowing, harvesting, and overuse of land, disturb soil and expose it to erosion.
Tilling or plowing increases soil exposure to erosion.
Continuous cropping and monoculture can degrade soil structure, increasing erosion risk.
Mountain slope farming without measures like terracing accelerates erosion.
Overgrazing: Too many animals on a grassland area can destroy vegetation, leaving soil bare and prone to erosion.
Economic Activities: Extracting natural resources, such as metals or fossil fuels, disturbs land and causes erosion.
Developmental Activities: Construction for housing, transport, and recreation disturbs the land, leading to soil erosion and disrupting natural drainage.
Consequences of Soil Erosion
Loss of Nutrients and Organic Matter
The fine particles of topsoil, which contain essential nutrients and organic matter for plants, are lost due to soil erosion.
Wind erosion removes finer soil material, including organic matter, clay, and silt in a suspended (colloidal) form, leaving behind coarser, less fertile soil.
Removal of Seeds and Seedlings
Erosion may remove seeds or seedlings, resulting in bare soil.
Bare soil is more vulnerable to erosion by both wind and water, reducing the soil's ability to retain water.
Siltation and Sedimentation
Sheet, rill, gully, and streambank erosion cause siltation of rivers, streams, and fields.
Silt deposition damages crops and pastures, leading to sedimentation in water bodies such as streams, dams, and reservoirs.
Sedimentation degrades water quality, damaging aquatic habitats and organisms.
Formation of Gullies
Gully erosion leads to significant soil loss, sometimes creating gullies up to 30 meters deep.
These large gullies disrupt normal farming operations and reduce usable land area.
Streambank Erosion and Land Loss
Streambank erosion causes loss of land and can alter the course of rivers or streams.
This erosion damages public roads and deposits soil particles onto fertile agricultural fields.
Landslides and Mass Movements
The mass movement of land, such as landslides, inhibits farm production and land use.
Landslides pose a threat to animals and humans, sometimes leading to mortality.
Coastal Erosion
Coastal erosion leads to the encroachment of sand over adjacent land.
Prevention of Soil Erosion
Retaining Vegetation Cover
Maintaining vegetation cover ensures that soil is not exposed to rain.
Roots of plants hold soil particles together, intercept rainfall, and protect soil from the direct impact of raindrops.
Controlling Cattle Grazing
Cattle grazing should be controlled to prevent damage to vegetation and soil.
Adopting Crop Rotation and Fallowing
Practicing crop rotation and leaving the land fallow (not planting anything for some time) enhances soil health.
Improving Vegetation and Soil Management
Enhance vegetation and soil management to increase soil organic matter.
Preventing Stream Bank Erosion
Runoff water should be stored in the catchment area by maintaining vegetation cover or constructing dams for water storage.
Controlling Coastal Erosion
Re-establish protective vegetation along beaches to reduce or prevent coastal erosion.
Minimize disturbance to coastal dunes and avoid construction near dune systems.
Maintaining Sandy Soil Vegetation
Keep vegetation cover over sandy soils above 30%.
Reduce wind exposure to the soil by leaving stubble or mulch on the surface. (Stubble refers to crop remains after harvesting.)
Planting Shelter Belts
Plant trees in the form of a shelter belt to reduce wind speed and prevent soil erosion.
Slight degradation refers to the condition where crop yield potential is reduced by 10%.
Land Degradation Affected Indian States
Moderate degradation refers to a 10-50% reduction in yield potential.
Severe degradation means that the land has lost more than 50% of its productive capacity or yield potential.
Causes of Land Degradation
Use of agrochemicals (chemical fertilizers and pesticides)
Excessive irrigation
Cultivation of high yielding plant varieties
Causes of World Land Degradation
Agrochemicals and Their Harmful Effects on Land
Agrochemicals are used for two main purposes:
Replenishing or replacing soil nutrients using chemical fertilizers.
Destroying plant pests with toxic chemicals called pesticides.
Adverse effects of chemical fertilizers:
Excessive use of chemical fertilizers containing macronutrients like nitrogen, phosphorus, and potassium (NPK) causes a deficiency in micronutrients like zinc, iron, copper, etc., leading to decreased soil productivity.
Unused fertilizers are washed away with rainwater, causing eutrophication or algal blooms that harm aquatic life.
Excess nitrates from fertilizers leach into water bodies, potentially causing methemoglobinemia, especially in bottle-fed infants.
Adverse effects of plant protection chemicals:
Biocides are toxic chemicals used to kill pests, but they also harm non-target organisms and remain active long after their intended purpose, making them harmful.
Problems Due to Excessive Irrigation
Waterlogging: Excessive irrigation without proper drainage raises the water table, making the soil waterlogged. This leads to poor plant growth due to a lack of oxygen in the soil, weakening plant roots.
Salt Affected Soil: In hot climates, excessive irrigation causes salt accumulation in the soil, reducing productivity. Plants in saline soil face water stress even when moisture is available.
Impact of High Yielding Plant Varieties (HYV) on Soil Degradation
High Yielding Varieties (HYV) have increased food production but require extensive use of irrigation, fertilizers, and pesticides, contributing to soil degradation.
Measures for Preventing Soil Erosion and Land Degradation
Measures for Preventing Soil Erosion and Land Degradation
Tree Planting:
To prevent wind erosion, trees should be planted to break the force of the wind. The trees not only protect the soil from the sun, wind, and water, but they also help hold soil particles in place.
Cultivation and Farming Techniques:
Cultivation of land at right angles to wind direction: This helps reduce soil erosion by wind.
Ploughing Style: Tilling the field at right angles to the slope (counter ploughing) helps reduce soil erosion. The ridges created act like tiny dams that help water seep into the soil instead of running down freely, preventing soil pollution. Contour ploughing can reduce soil erosion by up to 50%.
Terrace Farming and Contour Ploughing
Strip Farming: This method involves planting main crops in widely spaced rows and filling the spaces with another crop to ensure complete ground cover. This reduces water flow and helps water soak into the soil, thus reducing erosion.
Terracing: This method is used to reduce soil erosion on mountain slopes by leveling areas to prevent water flow. However, terraces can erode and require maintenance.
Timing of Tillage: The season in which fields are tilled can affect erosion. Tilling in the fall exposes the soil to erosion all winter. If the field is tilled in spring, erosion is minimized as the ground cover remains longer.
No-Till Cultivation: Specialized machinery can loosen the soil, plant seeds, and control weeds with minimal disturbance to the soil, helping to prevent erosion. However, this can increase weed and insect populations due to reduced removal.
Polyvarietal Cultivation: Planting several varieties of the same crop ensures that the field is not exposed all at once, thus protecting it from erosion.
Addition of Organic Matter: Ploughing in crop residues or crops grown for this purpose helps to decompose into sticky polysaccharides that bind soil particles together, reducing erosion.
Agricultural Technologies for Preventing Soil Degradation:
Organic Farming or Green Manures:
Instead of chemical fertilizers, nitrogen-fixing bacteria in legume root nodules can improve soil nitrogen levels. Organic fertilizers like cow dung and agricultural waste can also improve soil nutrients, reducing the need for chemical fertilizers and minimizing their toxic effects.
Biofertilizers:
Microorganisms play an important role in soil fertility by improving soil structure, adding nutrients, and improving physical conditions. Various microorganisms are used as biofertilizers to enhance soil fertility.
Biological Pest Control:
Natural predators and parasites of pests help control plant pests and pathogens without entering the food chain or poisoning animals. They are safe for humans and are increasingly used in modern farming.
Problems of Deforestation and Conservation measures
Problems of Deforestation and Conservation Measures
Forests are ecological as well as socio-economic resources. Forests have to be managed judiciously not only because they are the source of various products and industrial raw materials but also for environmental protection and various services they provide. Approximately 1/3rd of the earth’s total land area is covered by forests. The forests provide habitat for wildlife, resources such as timber, firewood, drugs, etc., and an aesthetic environment. Indirectly, the forests benefit people by protecting watersheds from soil erosion, keeping rivers and reservoirs free of silt, and facilitate the recharging of groundwater.
Deforestation
Deforestation is a very broad term, which consists of cutting of trees including repeated lopping, felling, and removal of forest litter, browsing, grazing, and trampling of seedlings. It can also be defined as the removal or damage of vegetation in a forest to the extent that it no longer supports its natural flora and fauna.
Causes of Deforestation
The most common reason for deforestation is the cutting of wood for fuel, lumber, and paper. Another important cause relates to the clearing of forest land for agriculture, including conversion to cropland and pasture. The main causes of deforestation are:
Agriculture: The expanding agriculture is one of the most important causes of deforestation. As demands for agricultural products rise, more and more land is brought under cultivation, and for that more forests are cleared. The forest soils after clearing are unable to support farming for long periods due to exhaustion of nutrients. Once the soils become unfit for cultivation, the area suffers from soil erosion and degradation.
Shifting Cultivation: Shifting cultivation or Jhoom farming is a 12,000-year-old practice and a step towards the transition from food collection to food production. It is also known as the slash-and-burn method of farming. Annually about 5 lakh hectares of forest are cleared for this type of farming. Even today, shifting cultivation is practiced in the states of Assam, Manipur, Meghalaya, Mizoram, Nagaland, Tripura, and the Andaman and the Nicobar Islands.
Demand for Firewood: Firewood has been used as a source of energy for cooking, heating, etc. Almost 44% of the total global wood produced fulfills the fuel requirements of the world. India consumes nearly 135-170 Mt (Million tons) of firewood annually and 10-15 ha of forest cover is being stripped off to meet the minimum fuel needs of urban and rural poor.
Wood for Industry and Commercial Use: Wood, the versatile forest produce, is used for several industrial purposes, such as making crates, packing cases, furniture, matchboxes, wooden boxes, paper and pulp, plywood, etc. Unrestricted exploitation of timber, as well as other wood products for commercial purposes, is the main cause of forest degradation. For example, the apple industry in the Himalayan region has led to the destruction of fir and other tree species.
Urbanization and Developmental Projects: Often urbanization and developmental activities lead to deforestation. The process of deforestation begins with the building of infrastructure in the form of roads, railway lines, the building of dams, townships, electric supply, etc. Thermal power plants, mining for coal, metal ores, and minerals are also important causes of deforestation.
Overgrazing of forests by animals mainly in the tropical and subtropical areas has resulted in large-scale degradation of natural vegetation.
Causes of Tropical Degradation
Other Causes: Recent developments everywhere in the world have caused large-scale environmental degradation, especially in tropical forest areas. Forest fires, whether natural or man-made, are effective destroyers of forest covers.
Consequences of Deforestation
Soil Erosion and Flash Floods: A shrinking forest cover coupled with overexploitation of groundwater has accelerated erosion along the slopes of the lower Himalayas and Aravali hills, making them prone to landslides. Lack of forest cover has resulted in water flowing off the ground, washing away the topsoil which is finally deposited as silt in the river beds.
Climatic Change: Forests enhance local precipitation, improve the water holding capacity of the soil, regulate the water cycle, and maintain soil fertility by returning the nutrients to the soil through leaf fall and decomposition of litter. Forests have a profound effect on the climate. They absorb carbon dioxide from the atmosphere and help in balancing carbon dioxide and oxygen in the atmosphere.
Loss of Wildlife: The destruction and alteration of habitats due to deforestation causes an ecological imbalance in the region concerned. The shrinkage of green cover has adverse effects on the stability of the ecosystem.
Conservation Measures
The protection and conservation of forest resources are not only desirable but are also necessary for the economic development of a nation and the maintenance of environmental and ecological balance. Integrated Conservation Research (ICR) has launched massive programs of forest conservation in collaboration with UNESCO’s MAN AND BIOSPHERE (MAB) program.
The National Forest Policy of India has laid down certain basic principles for proper management and conservation of the forest resources of the country such as:
Classification of forests according to functional aspects into protected forests, reserved forests, village forests, etc.
Expansion in the forest cover by planting trees in order to ameliorate the physical and climatic conditions for the welfare of the people.
Provision for ensuring progressive increasing supplies of fodder for animals and timber for agricultural implements and firewood to local inhabitants nearer to the forests.
Opposition to the reckless extension of agricultural land at the cost of forest land.
Extension of the forested area by the massive plan of tree plantation on a large-scale at war-footing so as to bring 33 percent of the country’s geographical area under forest.
An important measure of effective conservation of natural forest is to adapt the scientific and judicious method of cutting trees by following a selective approach.
The Integrated Conservation Research has suggested elaborate programs for the betterment of forests, including agroforestry, ethnobotany, and natural history-oriented tourism.
Remedial Measures
Intensive development schemes for afforestation should be adopted. High yielding varieties should be planted in suitable areas.
Proper arrangements to save forests from fires and plant diseases.
A thorough inventory of forest resources is necessary to make an accurate assessment of our forest resources and make plans for their proper use.
Shifting cultivation should be discouraged and tribals depending on this type of cultivation should be provided with alternative sources of livelihood.
People associated with forest protection should be properly trained.
Government Initiatives
Survey and inventorisation of floral and faunal resources are carried out by Botanical Survey of India (BSI) and Zoological Survey of India (ZSI).
Biological Diversity Act 2002 has been enacted and Biological Diversity Rules 2004 have been notified, which aim at the conservation of biological resources of the country.
Industries to obtain “Consent for Establishment” as well as “Consent to Operate” under the provisions of the Water Act, 1974 and Air Act, 1981.
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