What is Soil and Soil Profile.

Soil:- a portion of the regolith which supports the growth of plants is called soil. Thus soil is a combination of minerals, organic matter water, and air.

Regolith:- any solid unconsolidated material lying on top of bedrock is called regolith. It includes soil, alluvium and rock fragments weathered from the bedrock. The thickness of this mantle varies from nil over rock exposure to very deep in areas protected from erosion.

Soil profile:-if we examine the walls of a trench, they are found to contain a series of horizontal layers. These layers are called horizons. All horizons together form the soil profile. The three basic horizons from top to bottom are “O”, “A”, “B”, “C” ,”D”.


  • A – Horizon:- it is the upper most layer of the soil profile. It is also called surface soil. This layer contains organic matter and micro- organisms. In these layers the greatest biological activity takes place.
  • B – Horizon:-this horizon is called sub soil. This intermediate zone is also called the zone of accumulation as much of the material which is leached out from A- horizon is deposited here.
  • C – Horizon:-the lower horizon is called c – horizon. It mainly consists of the partly altered parent rock material.soil, the soil
  • Types of soil:-depending upon their mode of formation the soil deposits have been broadly grouped into two class
    • Residual soil:- in plain areas the products of rock weathering continue to accumulate in place over the parent rock masses and give rise to a “ residual soil deposit”. As the action of weathering decreases with depth. The common examples of residual soil are laterite, terra-rosa and peat bogs.
    • Transported soil:- the weathered and broken rocks materials are eroded and transpoted from one place to another by natural agencies such as wind , water, ice, gravity. The deposits of soil formed in this manner are called “transported soil deposits”.


    Transporting agency      –       nature of soil

    • Rivers         – alluvial deposits
    • Lakes          – lacustrine deposits
    • Sea             – marine deposits
    • Wind          – eolian deposits
    • Glaciar        – glacial deposits
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