Soil is the topmost layer of the earth's surface.It consists of rocks and mineral particles mixed with the organic matter. Soil formation begins with the breakdown of rocks and other materials into smaller pieces on the surface of the earth. Soil supports the growth of plants. It is home to many organisms and essential for agriculture.

Polythene bags and plastics pollute the soil and kill the microorganisms that live in the soil. Industries empty their sludge and pollutants into the air, soil and water.

Soil is composed of different layers. Humus is the top most layer of soil as it is lighter in weight.In order of the increasing size the subsequent layers are clay, sand and gravel.

Soil profile is a vertical section through different layers of the soil. These layers are identified on the basis of texture, colour, chemical composition, depth and particle size. These layers are known as horizons. Horizon A is known as topsoil. It is fertile and dark in colour due to humus. It is soft, porous and retains more water. It provides shelter for living organisms like beetles, etc. and support to plants. Horizon B contains lesser amount of humus and more minerals. It is harder and compact. Horizon C consists of small lumps of rocks with cracks and crevices. It is harder than B-horizon. Bedrock consists of rocks. It is hard and difficult to dig.

On the basis of proportion of particles of various sizes, soil is classified into sandy soil, clayey soil and loamy soil.

In sandy soil, proportion of big particles is more. It is well-aerated due to small spaces between its particles. In clayey soil, proportion of fine particles is more. It shows more water holding capacity. It is used to make pots, statues and toys.

In loamy soil, amount of fine and big particles is same. This type of soil is best for plants.

Other types of soil are residual soil, transported soil and mountainous soil.

Soil which remains at the place of its formation is called residual soil. Soil settled at places other than its place of formation, as a result of its transportation by gravity, flowing water, winds and glaciers is called transported soil. Soil usually found in depressions, valley basins or on gently inclined slopes is called mountainous soil.

Percolation rate refers to the amount of water that can pass through the pores of the soil in unit time(1 min).

Soil moisture is the amount of water present in the soil.Water absorption refers to the maximum amount of water that can be absorbed by a given amount of soil.

Soil erosion is the removal of topsoil by water, wind or ice. It is caused due to deforestation. It can be prevented by planting more plants. Plant roots firmly hold the soil andprevent soil erosion. Afforestation in the affected areas can play an important role in soil conservation.

Crops grown in an area depend on the type of soil and climatic conditions.

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