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Soil Profile

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Soil Profile - Lesson Summary

Soil is the upper layer of earth in which plants grow and is usually composed of a mixture of organic remains, clay, and rock particles.
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Soil is the upper layer of earth in which plants grow and is usually composed a mixture of rock particles and humus.
Soil is a natural resource that is essential for life. Soil is used as a source for food, clothing, shelter, minerals, coal, bricks, mortar, pottery and porcelain. Soil provides water and minerals to plants for their growth. Thus all living organisms depend on soil.

Soil Formation - Weathering:
Soil is formed when rocks are broken down by the action of wind, water and climate. This process is called weathering. The characteristic features of a soil depend upon the rocks from which it has been formed and the kind of plants that grow in it.

Weathering Types:  Weathering is of two types
     •  Physical Weathering
     •  Chemical Weathering

Physical Weathering:  Physical weathering is also termed as mechanical weathering, in which the composition of the original rock is unaffected. In this process the rocks and landforms are broken down into smaller pieces by physical forces like wind, frost, ice and temperature changes.

Chemical Weathering:  In this process the mineral composition of the rock get changed due to the action of chemical agents like water, oxygen, carbon dioxide, etc. This is caused when chemical agents like water reacts with minerals in rocks to form new minerals and soluble salts.
 
Soil Profile:  If you examine the sides of a ditch that has recently been dug up or the sides of a road on a hill, you will find that the soil forms layers of particles of different sizes. You will notice that each layer is different from the other in texture, colour and chemical composition. Even the thickness of each layer is not the same. 
A vertical section that shows different layers of soil is called a soil profile. Each layer is called a horizon.
Horizons are classified into 4-types. They are,
     •  Top soil or Horizon-A
     •  Middle layer or Horizon-B
     •  Horizon-C
     •  Bed rock

Horizon-A: The topmost layer is dark in color, and contains the remains of dead plants and animals. This rotting matter is called humus.
This layer of soil is called topsoil or A-horizon.
It is made up of humus and minerals, and makes the soil fertile.
It is soft and porous, and can retain more water than the other layers.
Many tiny organisms, such as beetles, worms and rodents, live in the topsoil. The roots of small plants do not go down very deep and can be found in the topsoil. 

Horizon-B: The layer below the topsoil is called B-horizon or the middle layer.
The middle layer is less porous than the topsoil, and is, therefore, harder.
It contains more minerals as compared to the topsoil, but less quantity of humus.
 
Horizon-C: It is not as compact as the two layers above it. This layer is called C-horizon.
It has cracks running through it.
It is mostly made up of rocks.
 
Bedrock: The bottom-most layer in the soil profile is called bedrock.
This is far more solid in composition than the other layers and is very hard. This layer consists of the parent rock.


 
Soil erosion:  Soil erosion is removal of land surface by agents like floods, wind and ice. Plant roots firmly bind to the soil. When trees are removed soil become loose and it easily carried away by wind or flowing water. Soil erosion is severe in areas of little or no surface vegetation, such as deserts and barren lands. Therefore, cutting of trees and deforestation should be prevented and efforts should be made to increase greenery.

Due to soil erosion the fertile soil is washed away. This causes a decrease in the net fertile land available for cultivation.

The major causes of soil erosion:
     •  Deforestation
     •  Overgrazing
     •  Floods and heavy rain fall
     •  Improper farming

Prevention of soil erosion:
     •  Afforestation – Planting large number of trees.
     •  Constructing dams - Floods can be controlled by constructing dams.
     •  Construction of embankment or mud walls around hill slopes to prevent flow of water.
     •  Adopting terrace farming in hilly areas - In this method the ground is cut into large steps called terraces. On each level suitable crops are grown. This reduces the speed with which water flows down, water stops at each level. In this way higher terrace will get enough water and soil erosion is reduced. 

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