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. |