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Soil - Lesson Summary

Soil is the thin layer of matter that covers the earth’s surface, made up of organic matter, minerals and weathered rocks.

Weathered rocks are a result of the breakdown and decay of rocks by changes in temperature, frost and actions of living organisms. This process is very slow, and is called weathering.  During weathering, rock debris gets mixed with organic matter and minerals, increasing the fertility of the soil.

There are a number of factors that affect the physical and chemical properties of soil in a landform.
The primary factors are parent rock and climate in the area. The parent rock from which the soil is formed, influences its: Colour, Texture, Chemical properties, Mineral content and Permeability.

Climatic conditions, like temperature and rainfall, determine the rate of weathering and the formation of humus. The other factors that affect soil formation are: Relief, Flora, fauna and micro-organisms and Time.

Steep slopes are more prone to soil erosion, so the layer of soil on them may not be very thick. Low-lying, flat areas retain the layers of sediments for longer periods, and thus, have a thick layer of soil.  Living or organic matter, like plants, animals and micro-organisms, influence the rate of humus formation.

Humus is the degraded organic material in soil and helps increase its fertility. The process of decomposition is helped by micro-organisms that break down the organic matter when they feed on it.

The thickness of the soil profile is affected by the time taken for the soil to form. Older soil has a thicker soil profile, as over time, several layers of soil have been deposited and formed. The types of soil found in India include: Alluvial, Black, Red, Laterite, Desertand and Montane soil.

Soil erosion occurs when soil and rock particles are carried away by wind, water or ice, and deposited in another location. Soil depletion takes place when the nutrients in soil are removed and are not replaced. It affects the quality and fertility of the soil.

Soil degradation is caused by: Deforestation, Overgrazing, Excessive use of chemical fertilisers and pesticides, Rain wash, Landslides and Floods.

Some methods to conserve soil quality are: Mulching, Contour barriers, Rock dams, Terrace farming, Intercropping, Contour ploughing and Shelter belts.

Mulching helps to trap moisture in the soil and moderate soil temperature and involves covering the bare ground between plants with a layer of organic material like straw.

Contour barriers refer to barriers of stone, grass and soil built along the contour lines of a slope. Trenches are built in front of the barriers to collect water and prevent it from flowing down the contours and washing away the soil.

Rock dams are dams created from piles of rocks that are stacked up to slow down the flow of water and prevent the formation of gullies. This curtails soil erosion.

To provide flat surfaces for farming on steep slopes, terraces are created. This is called terrace farming. Using terraces also prevents soil erosion and surface run-off.

Intercropping is a widely used practice in China to reduce soil erosion due to rain wash. In this method, different crops are grown in alternate rows and are sown at different times.

Contour ploughing is the method of soil conservation in which the land is ploughed parallel to the contours of a slope. This creates a barrier that prevents water from flowing down the slope.

In coastal and dry areas, rows of trees are planted to control the movement of wind, thus protecting the soil from being blown away. These rows of trees act as shelter belts.


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