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  • Soil is a naturally occurring substance that is valuable in sustaining life on earth.
  • Humus – It is a component of soil that is formed from the dead and decayed organic matter.
  • Weathering – It is the process of formation of soil by breaking down of rocks. It occurs by the action of wind, water, and climate.
  • Soil profile – It is a vertical section through various layers of soil. These various layers are known as horizons.
  • There are four types of horizons.
    • A-horizon or topsoil– It is the top most soil, which is dark in colour and rich in humus. It is soft, porous, and has the ability to retain water.
    • B-horizon – It is the middle next layer of the soil profile. It has lesser humus and more minerals. The layer is harder and more compact.
    • C-horizon – It is the third layer made up of small lumps of rocks with cracks and crevices.
    • Bedrock – It is the lowermost hard layer and difficult to dig with a spade.

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