The thin layer of grainy substance covering the surface of the earth is called soil. It is a dynamic
medium in which many chemical, physical and biological activities go constantly.
* Soil is made up of organic matter, minerals and weathered rocks found on the earth.
* Soil is a medium for growth and its characteristics keeps on fluctuating according to the seasons.
Factors of Soil formation
Parent Rock: It determines colour, texture, chemical properties, mineral, content and permeability.
Topography: The influence of topography is felt through the amount of sunlight, slopes, altitude determine the accumulation of soil.
Climate: Temperature, Rainfall, rate of weathering and humus have their influence upon soil formation.
Biological Activity: Flora, Fauna and micro organisams affect the rate of humus formation.
Time: The length of time the soil forming processes operate, determines the maturation of soils & profile development.
Types of soils found in India
In India, soils could be
* Alluvial soils
* Black soils
* Red and yellow soils
* Laterite soils
* Desertic and
* Mountain soils
* These soils cover about 40% of the total surface area of the country and are widespread in Northern plains & river valleys.
* These soils vary in nature from sandy loam to clay and are generally rich in potash.
* "Khadar" is the new alluvium which is deposited by floods annually.
* "Bhangar" represents the system of older alluvium deposited away from flood plains.
* The colour of these soils vary from light grey to ash grey.
* These soils are intensively cultivated.
* It covers most of the Deccan Plateau.
* These soils are also known as "Regular Soil" or "Black cotton Soil".
* These are generally clayey, deep and impermeable.
* Due to the character of slow absorption and loss of moisture, these soils retain the moisture for a very long time which helps the crops to sustain even during dry.
* These are rich in Lime, Iron, Magnesia, Alumina and Potash.
* The colour of the soil varies from deep black to grey.
Red and Yellow Soils:
* Red Soil found in the eastern and southern part of the Deccan Plateau and crystalline in form.
* Yellow soil looks yellow when it occurs in a hydrated form.
* Yellow and red soils are found in Odisha, Chattisgarh and in the southern parts of middle Ganga plain.
* These are poor in fertility.
* It is derived from the Latin word "Later" which means brick.
* Laterite soils are found in the areas with high temperature and high rainfall.
* These soils are poor in organic matter, nitrogen, phosphate, calcium and hence these soils are unfit for cultivation.
* Laterite soils are widely cut as bricks for use in house construction.
* These soils are found in Karnataka, Kerala, Odisha, Assam, Tamilnadu and Madhya Pradesh.
* Red laterite soils in Tamilnadu, Andhra Pradesh and Kerala are more suitable for tree crops like "Cashewnut".
* These soils are sandy in structure and saline in nature.
* These range from red to brown in colour.
* Due to dry climate, high temperature, accelerated evaporation they lack moisture and humus.
* These are developed in western Rajasthan.
* These soils vary in structure and texture depending on the mountain environment where they are formed.
* These are loamy and silty on valley sides and coarse grained in the upper slopes.
* The destruction of the soil cover is described as "Soil erosion."
* The rate of removal of fine particles from the surface is same as the rate addition of particles to the soil layer.
* Wind and water are powerful agents of soil erosion because of their ability to remove soil and transport it.
* Human activities like deforestation and population increase are also responsible for soil erosion.
* Our country is losing about 8,000 hectares of land every years due to Soil erosion.
* Soil erosion and depletion are the major threats to soil as a resource.
* Factors which lead to soil degradation are deforestation, overgrazing, overuse of chemical fertilisers or pesticides, rain wash, land slides and floods.
Soil Conservation measures
* The bare ground between plants is covered with a layer of organic material like straw.
* It helps to retain soil moisture.
(ii) Contour Barriers:
* Stones, grass, soil are used to build barriers along contours.
* Trenches are made infront of barriers to collect water.
(iii) Rock dam:
* Rocks are piled up to slow down the flow of water. Thus prevents gullies and further soil loss.
(iv) Terrace Farming:
* Broad flat steps or terraces are used to grow crops.
* These reduce the surface run-off and the soil erosion.
(v) Inter Cropping:
* Different crops are grown in alternate rows and are sown at different times to protect the soil from rain wash.
Ploughing parallel to the contours of a hill slope to form a natural barrier for water to flow down the slope.
In the coastal and dry regions, rows of trees are planted to check the wind movement to protect soil cover.