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Answer» Soil is commonly stratified into horizons at different depth. These layers differ in their physical, chemical and biological properties. This succession of super-imposed horizons is called soil profile. | Horizon | Description | | O-Horizon (Organic horizon) Humus | It consists of fresh or partially decomposed organic matter. O1 – Freshly fallen leaves, twigs, flowers and fruits. O2 – Dead plants, animals and their excreta decomposed by microorganisms. Usually absent in agricultural and deserts. | | A-Horizon (Leached horizon) Topsoil – Often rich in humus and minerals. | It consists of top soil with humus, living creatures and in-organic minerals. A1 – Dark and rich in organic matter because of mixture of organic and mineral matters. A2 – Light coloured layer with large sized mineral particles. | | B-Horizon (Accumulation horizon) (Subsoil – Poor in humus, rich in minerals) | It consists of iron, aluminium and silica rich clay organic compounds. | | C – Horizon (Partially weathered horizon) Weathered rock Fragments – Little or no plant or animal life. | It consists of parent materials of soil, composed of little amount of organic matters without life forms. | | R – Horizon (Parent material) Bedrock | It is a parent bed rock upon which underground water is found. |
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