Open Text Material
SUBJECT –SCIENCE
CLASS- VII
THEME-I: - Soil-Erosion and Conservation
What is soil erosion?
Wind, rain, floods, rivers, glaciers and earthquakes all erode (wear away) the land. Soil erosion occurs when
soil moves (for example sliding down a slope) to a different place. This may be only a short distance, or
carried many kilometres away by rivers.
Soil-Layers
The two top layers are:
 Topsoil, which holds food and water needed by plants
 Subsoil, under the topsoil, which anchors plant roots, and holds water. Both can be affected by
erosion.
Some types of erosion
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Slip or landslide – after a rainstorm or earthquake, soil may slide down a slope.
Rills – heavy rain running down slopes can gauge small channels (rills) into the soil.
Scree – loose mountain rocks, which are unstable and slide downhill.
Streambank – flooded rivers and streams wear away the banks.
Impact of human beings
Human beings have sped up soil erosion. New Zealand’s native forests once protected the soil, and tree roots
kept subsoil stable. But settlers burnt the trees and planted pasture for sheep and cattle. Rain and floods
began washing away the topsoil. On some hill country, soil slid down the slopes.
Where bare soil was exposed to wind, frost and rain, the topsoil was easily eroded.
Damage to New Zealand’s hill country and other farmland costs up to $150 million annually.
Impact of animals
The settlers brought rabbits, deer, possums, sheep and cattle. The animals ate and trampled plants and trees,
exposing the soil to rain and wind.
Where does the soil go?
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Down to flatter land, where it may block roads and damage houses.
Into streams and rivers, harming water and wildlife.
Out to sea.
Soil conservation
Soil conservation is a set of management strategies for prevention of soil being eroded from the Earth’s
surface or becoming chemically altered by overuse, acidification, salinization or other chemical soil
contamination. It is a component of environmental soil science.
Erosion barriers on disturbed slope, Marin County, California
Prevention of Soil Erosion
Contour plowing, Pennsylvania 1938. The rows formed slow water run-off during rainstorms to prevent soil erosion
and allows the water time to settle into the soil.
Since the 1940s, many methods have been used to save the soil and prevent erosion, including:
 planting trees
 using new farming methods
 stopping rivers flooding
 building small dams in gullies to slow down water run-off
 digging channels across farm slopes to divert water
 protecting areas likely to be eroded.
Crop rotation is simply the conventional alternation of crops on a given field, so that nutrient depletion is
avoided from repetitive chemical uptake/deposition of single crop growth.
Practices
There are many practices that farmers have invoked for centuries. These fall into two main categories:
contour farming and terracing. There are many erosion control examples such as conservation tillage, crop
rotation, and growing cover crops.
Terracing is the practice of creating benches or nearly level layers on a hillside setting. Terraced farming is
more common on small farms and in underdeveloped countries, since mechanized equipment is difficult to
deploy in this setting.
Human overpopulation is leading to destruction of tropical forests due to widening practices of slash-andburn and other methods of subsistence farming necessitated by famines in lesser developed countries. A
sequel to the deforestation is typically large scale erosion, loss of soil nutrients and sometimes total
desertification.
Wind-Breaks
Windbreaks are created by planting sufficiently dense rows of trees at the windward exposure of an
agricultural field subject to wind erosion.Evergreen species are preferred to achieve year-round protection.
SAMPLE QUESTIONS FOR PRACTICE
1) a) What are the different types of soil erosion?
b) What are the different methods to prevent soil erosion?
2) In context to the given theme explain the types of farming method/practices–
a) Hillside areas of our country?
b) Areas subject to wind erosion?
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