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What is Soil Erosion? Causes and Effects of Soil Erosion – How to prevent Soil Erosion?

What is Soil Erosion? Causes and Effects of Soil Erosion – How to prevent Soil Erosion?

Relevance:

  • GS 3 II Geography II Indian Physical Geography II Soil

Why in the news?

Soil erosion is one of the most common issue, but hardly is covered by main stream media neither ministry and authority takes any concern issue

What is soil erosion?

  • Soil erosion is the displacement of the upper layer of soil; it is a form of soil degradation.
  • This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolean) erosion, zoogenic erosion and anthropogenic erosion
  • Human activities have increased by 10–50 times the rate at which erosion is occurring globally. Excessive (or accelerated) erosion causes both “on-site” and “off-site” problems.
  • On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers.

Types of soil erosion:

  • Splash erosion: In splash erosion, the impact of a falling raindrop creates a small crater in the soil, ejecting soil particles. The distance these soil particles travel can be as much as 0.6 m (two feet) vertically and 1.5 m (five feet) horizontally on level ground.
  • Sheet erosion: If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs. If the runoff has sufficient flow energy, it will transport loosened soil particles (sediment) down the slope. Sheet erosion is the transport of loosened soil particles by overland flow
  • Rill erosion: refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimeters (about an inch) or less and along-channel slopes may be quite steep
  • Gully erosion: It occurs when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth
  • Bank erosion: It is the wearing away of the banks of a stream or river. This is distinguished from changes on the bed of the watercourse, which is referred to as scour.
    • Erosion and changes in the form of river banks may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times
  • Thermal erosion: It is the result of melting and weakening permafrost due to moving water. It can occur both along rivers and at the coast. Rapid river channel migration observed in the Lena River of Siberia is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials
  • Wind erosion: It is a major geomorphological force, especially in arid and semi-arid regions. It is also a major source of land degradation, evaporation, desertification, harmful airborne dust, and crop damage— especially after being increased far above natural rates by human activities such as deforestation, urbanization, and agriculture

Factors affecting soil erosion:

  • Climate: The speed and duration of the wind have a direct relationship to the extent of soil erosion. Soil moisture levels are very low at the surface of excessively drained soils or during periods of drought, thus releasing the particles for transport by win
  • Soil structure and composition: Soil surfaces that are not rough offer little resistance to the wind. However, ridges left from tillage can dry out more quickly in a wind event, resulting in more loose, dry soil available to blow. Over time, soil surfaces become filled in, and the roughness is broken down by abrasion. This results in a smoother surface susceptible to the wind
  • Vegetative cover: The lack of permanent vegetative cover in certain locations results in extensive wind erosion. Loose, dry, bare soil is the most susceptible; however, crops that produce low levels of residue (e.g., soybeans and many vegetable crops) may not provide enough resistance. In severe cases, even crops that produce a lot of residue may not protect the soil.
  • Soil Erodability: Based on the characteristics of each unique soil, it is more or less susceptible to erosion. Recurring erosion is more typical for soil in areas that have experienced erosion in the past.

Activities that increase soil erosion:

  • Unsustainable agricultural practices increase rates of erosion by one to two orders of magnitude over the natural rate and far exceed replacement by soil production.
  • The tillage of agricultural lands, which breaks up soil into finer particles, is one of the primary factors. The problem has been exacerbated in modern times, due to mechanized agricultural equipment that allows for deep plowing, which severely increases the amount of soil that is available for transport by water erosion.
  • In an undisturbed forest, the mineral soil is protected by a layer of leaf litter and an humus that cover the forest floor. These two layers form a protective mat over the soil that absorbs the impact of rain drops.
  • They are porous and highly permeable to rainfall, and allow rainwater to slow percolate into the soil below, instead of flowing over the surface as runoff.
  • The roots of the trees and plants hold together soil particles, preventing them from being washed away
  • Urbanization has major effects on erosion processes—first by denuding the land of vegetative cover, altering drainage patterns, and compacting the soil during construction; and next by covering the land in an impermeable layer of asphalt or concrete that increases the amount of surface runoff and increases surface wind speeds. Much of the sediment carried in runoff from urban areas (especially roads) is highly contaminated with fuel, oil, and other chemicals.
  • The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events.
  • The rise in sea levels that has occurred as a result of climate change has also greatly increased coastal erosion rates

Global Problem:

  • Erosion is a major problem affecting soils all over the world.
  • The rapid growth of the world’s population has resulted in increased cultivation of land. This puts more pressure on land and leads to soil losing its structure and cohesion, which means that it can be eroded more easily.
  • Heavy farming machinery can also ‘compact’ soil, which causes water to run straight off the surface after rain, taking soil particles with it, instead of infiltrating into the soil.
  • The total land area subjected to human-induced soil degradation is estimated at about 2 billion ha. Of this, the land area affected by soil degradation due to erosion is estimated at 1100 Mha by water erosion and 550 Mha by wind erosion.

Methods of controlling Soil Erosion:

  1. Biological methods: It includes the use of plant of vegetation cover.
  • Agronomic practices: It includes natural protection by growing vegetation in a manner that reduces soil loss. These are:
    • Contour farming: In which preparation of fields with alternate furrows and ridges to reduce water flow. Ridges at the same level are known as contour. On slopes, however, this type of farming is coupled with terracing.
    • Mulching: It is effective against wind as well as waster erosion. Some such plants as maize stalks, cotton stalks etc.., are used as a ‘mulch’ (a protective layer formed by the stubble). Mulches reduce soil moisture evaporation and increase amount of soil moisture by addition of organic matter to soil.
    • Crop rotation: It decreases soil loss and preserves the productivity of land.
    • Strip cropping: It involves the planting of crop in rows or strips to check flow of water
  • Agrostological methods: Grasses such as Cynodon dactylon are utilized as erosion-resisting stabilizer plants. They are grown in strips between the crops. Such methods include:
    • Hay farming: This aims to grow grasses in rotation with the fields crops, which helps in building up the structure of soil, preventing soil erosion and improving its fertility
    • Retiring lands to grass: It involves to grow grasses on such lands where major proportion of the top soil has been eroded.
    • Generally grasses are allowed to grazing under suitable climate conditions.
  1. Mechanical methods: These methods are used as supplements to biological methods. These are:
  • Basin listing: e. to construct small basin along the slope to intercept and divert the runoff water.
  • Contour terracing: To construct a channel along the slope to intercept and divert the runoff water. This may be:
    • Channel terrace: To dig channels at suitable intervals and the excavated soil deposited as a wide, low, ridge along, the lower edge of the channel.
    • Broad based ridge terrace: e. to construct ridge along both the sides of the channel
    • Bench terrace: To construct a number of platforms along contours or suitable graded lines across the slop
  • Stream bank protection: To grow vegetation alongside the river bank, to construct drains, concrete or stone Pitching etc. for checking & cutting and carving ‘of riverbanks.
  • Afforestation: Trees as windbreaks are planted at 90° to the prevailing wind in deserts which check the velocity of wind. They check the spread of sand dunes or desert conditions or blowing away of the fertile top soil. Windbreaks may be planted in several rows

Soil conservation methods:

  • Afforestation
  • Contour ploughing (cultivation against the direction of the wind).
  • Strip cultivation (cultivation in strips).
  • Flood control by government initiatives.
  • Reclamation of bad lands.
  • Wind breaks in land; like trees at borders.
  • Organic farming.
  • Control/restrict shifting cultivation.
  • Construction of proper drainage.
  • Leveling of gullies, ravines etc
  • Control of chemical fertilizers and pesticides in the market.
  • Proper awareness about the need of conservation.
  • Example of country who have successfully eradicated soil erosion:
    • Gunnarsholt, Iceland :Some areas have been successfully reclaimed, however, the land reclamation approaches used were small-scale and expensive. Today, land reclamation in this area focuses on establishing woody vegetation islands at selected locations in cooperation with local farmers as well as assisting them in reclaiming degraded areas around their homesteads through a program called “Farmers heal the land”.

Initiative taken by govt. for soil erosion:

  • In order to prevent soil erosion and land degradation, Ministry of Agriculture is implementing various watershed programmes, namely; National Watershed Development Project for Rainfed Areas (NWDPRA), Soil Conservation in the Catchments of River Valley Project and Flood Prone River (RVP&FPR) and Reclamation and Development of Alkali & Acid Soils (RADAS) across the country.
  • Ministry of Rural Development is also implementing Integrated Watershed Management Programme (IWMP) for the purpose.
  • About 57.61 million ha area has been developed under various watershed development programmes of Ministry of Agriculture and Ministry of Rural Development.
  • Besides, 1.5 million ha sodic land has been reclaimed using gypsum technology and 0.5 million ha saline land have been reclaimed using sub-surface drainage technology across the country.

Conclusion:

Soil erosion remains a key challenge for agriculture in several countries. Proper management of this valuable resource is vital to sustain long-term agricultural productivity. Soil conservation practices are tools the farmer can use to prevent soil degradation and build organic matter. These practices include: crop rotation, reduced tillage, mulching, and cover cropping and cross-slope farming.

Mains oriented question:

Explain the key causes and consequences of Indian soil erosion, as well as methods for preventing or erosing the soil? (200 words)