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Soil and Soil Formation

Soil is the surface layer of the earth’s crust that develops because of weathering and erosion.

Soil is made up of :

  • Organic matter.
  • Minerals.
  • Weathered rocks.
  • The type of soil in a region depends upon a variety of factors like relief, climate and parent rock material. The colour and structure of soil is dependent on these factors. The right mix of minerals and organic matter make the soil fertile.

    Let us look at the soil profile

    Soil Profile

    Soil Profile refers to the layers of soil. The major soil profiles are ……

  • Horizon O
  • Horizon A
  • Horizon B
  • Horizon C
  • Horizon O refers to the upper layer of soil, nearest the surface. It is commonly known as topsoil. In the woods or other areas that have not been ploughed or tilled, this layer includes organic litter, such as fallen leaves and twigs. The litter helps prevent erosion, holds moisture, and decays to form a very rich soil known as humus. Horizon o provides plants with nutrients they need.

    Horizon A is the layer below Horizon O. Litter is not present in horizon A and therefore there is much less humus. It consists of subsoil with sand, silt and clay.

    Horizon B is below Horizon A. Horizon B consists mostly of weatherized big rocks. This solid rock gives rise to the horizons above it.

    Horizon C is found below Horizon B and consists of parent rock.

    Soil profiles look different in different areas of the world. They are affected by climate and other things.

    Factors of Soil Formation



    The formation of soil happens over a very long period of time. It can take 1000 years or more.

    Factors that aid soil formation:


    Climate - Temperature, Rainfall influence rate of weathering and humus.

    Parent Rock - Determines colour, texture, chemical properties, mineral, content & permeability.

    Topography - Altitude and slope, determine accumulation of soil.

    Organic Material - Flora, Fauna and Micro-organism affect the rate of humus formation.

    Time Span - Determines thickness of soil profile.

    Soil is formed from the weathering of rocks and minerals. The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter. Over time this creates a thin layer of soil. Plants help the development of the soil. The plants attract animals, and when the animals die, their bodies decay. Decaying matter makes the soil thick and rich. This continues until the soil is fully formed. The soil then supports many different plants.

    The type of soil formed differs from place to place.


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