21 February 2014

Soil Profile

Soil is used in:
    • Agriculture
    • Gardens
    • Pottery
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.

Soil forms different layers of particles of different sizes. Each layer is different from the other in texture, colour and chemical composition. Even the thickness of each layer is not the same.
Soil Profile
A vertical section that shows different layers of soil is called a soil profile. Each layer is called a horizon.
Soil Profile, NCERT Notes, CBSE Notes, Class 7, Use of Soil
  • Top soil or Horizon-A
  • Middle layer or Horizon-B
  • Horizon-C
  • Bed rock
  • The topmost layer is dark in colour, 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.
When plastic bags are disposed off, they usually get embedded in the topsoil. Since plastic does not get decomposed naturally, the polythene bags pollute the soil and kill the organisms that live in it. Stop using polythene bags.
  • 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.
  • 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.
    • 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.
    • It is difficult to dig up this layer even with a spade.
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