5. Soil Erosion: Definition, Types, Conservation Methods | UPSC

What is Soil Erosion? What are its types, factors affecting it, and conservation methods? (Agriculture Optional UPSC)
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Topic: Soil Erosion flow chart
Topic: Soil Erosion

According to the National Bureau of Soil Survey & Land-use Planning(NBSS&UP) estimations, 119.2 million hectare area in India is prone to soil erosion. The annual rate of soil erosion in India is more than 16 tonnes per hectare, which is many times more than the acceptable limit which is 4-5 tonnes per hectare.

This causes fertility losses, loss of nutrients, and turning of cultivable land into wastelands. Thus, understanding soil erosion becomes very important from the agricultural point of view.

What is Soil Erosion

Definition: It is a natural geological process of wearing away of the earth’s top layer due to various natural agents as well as anthropogenic causes.

Accelerated Soil Erosion: When the rate of soil erosion exceeds the natural rate. It happens due to various anthropogenic reasons and is the major focus area when we generally talk about Soil Erosion.

Types of Soil Erosion

Although Soil Erosion can be classified on many basis, but, the one which is important for agriculture point of view is as follow:

Splash Erosion: When the raindrops strike the earth’s surface, it results in detachment and transportation of soil particles. The velocity of raindrops is generally 33 km/hr and can throw away the soil particles up to a few feet.

Splash Erosion; Picture courtesy: The Soil Erosion Site
Splash Erosion; Picture courtesy: The Soil Erosion Site

Sheet Erosion: When the upper layer of soil is uniformly removed by various natural and other agents of erosion. 

Sheet Erosion; Picture Courtesy : NRDC
Sheet Erosion; Picture Courtesy : NRDC

Rill Erosion: When the soil is eroded in small finger-like channels parallel to the slope, it is called rill erosion.

Rill Erosion; P.C. Wikipedia
Rill Erosion; P.C. Wikipedia

Gully Erosion: When the depth of rill erosion exceeds 0.3 meters, it is called gully erosion.

Gully Erosion; P.C. agri.we.gov.au
Gully Erosion; P.C. agri.we.gov.au

Ravines: When the gully erosion over time develops into large valleys and troughs with depths going as deep as 100 feet, it is called ravine erosion. In India, Chambal ravines are a good example of such a type of soil erosion.

Chambal Ravine; P.C. Indiatimes.com
Chambal Ravine; P.C. Indiatimes.com

There are some other types as well:

  • Slip Erosion: Slippage of landmass over a slope.
  • Stream Bank Erosion: Erosion by the rivers or streams along its banks.
  • Sea Shore: By the waves and tides of the sea.

Factors Affecting

  1. Rainfall:

Influence: 

  • Detach the soil particles.
  • Beating down of the surface.
  • Splashing of detached particles.

Factors:

  • Amount of rainfall.
  • Duration of rainfall.
  • The intensity of rainfall.
  • Frequency of rainfall.
  1. The slope of the land:

Factors to be considered here are:

  • The steepness of the land surface.
  • Length of the slope.
  • The shape of landmass.
  1. Vegetation Cover:
  • Protect the surface from the beating effect.
  • Provide mechanical obstruction to water.
  • Increase Infiltration.
  • Roots open the soils.
  1. Tillage Operations:

Proper Tillage > Improved Infiltration > Little Runoff

  1. Nature of Soil:
  • Texture: Sand/Silt/Clay
  • Structure: Particles, whether coarse or fine.
  • Organic Matter
  • Presence of hardpan under top layers.
  1. Presence of High Water Table

Splash Erosion Types (in Brief):

  1. Puddle Erosion: The beating and churning action of raindrops make the soil an impervious layer of surface mud.
  2. Fertility Erosion: Raindrops make the soil surface loose, causing erosion of fine particles, leaving behind the coarse material

Control: 

  • Prevent & reduce the force of raindrops by:
    • Growin crops & grasses.
    • Adding organic matter to the soil.
    • Stubble mulching.
  • Zero or Minimum Tillage.
  • Bunding or terracing against the slope.
  • Providing outlet channels covered with vegetation.

Principles for Erosion Control

  1. Reduce Surface runoff.
  2. Mechanical obstructions in the way.
  3. Reduce dispersion of soil particles.

Conservation Methods

  • Biological
    • Agronomical:
      • Cover Crops: Grass, Sunhemp, Berseem.
      • Strip Cropping: Monocot: taproot + Dicot: Fibrous roots.
      • Contour Strip Cropping
      • Crop Rotation
      • Mulching of the top layer
      • Organic Matter addition into the soil increases its water holding capacity as well as infiltration capacity.
    • Agrostological:
      • Growing Grass, groundnut, etc to protect the top layer.
      • Examples:
        • Dub (Cynodon dactylon)
        • Kudzu Vine
        • Kans (Sachharum spontaneum) on stream banks.
        • Dinanath (Pennisetum pedicullatum) on bunds or water outlets.
  • Mechanical
    • Contour tillage: Follow the natural slope.
    • Contour Bunding
    • Terracing: Alter the natural slope.
    • Outlet Channels covered with vegetation/grass
    • Basin Listing: Making basins against the slope to collect the running water.
    • Pan breaking: so that more water can infiltrate.
    • Water Harvesting: in-situ
    • Conservation tillage practices.

Soil erosion is detrimental to crop production and in long run makes the soil unfit for crops. Thus, for the food security of the nation, it becomes really important that this problem is solved on a priority basis.

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Reference

Aarti Kelkar Khambete/indiawaterportal.org

Nemraj Sunda/A Competitive Book Of Agriculture

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