Soil is a layer produced by the gradual weathering of the rock and covers the upper most surface. Development of soil depends on the several factors like Climate, Time, Topography, Parent rock, Biological activity etc.
Soil Profile :
The soil profile is the sequence of soil material found in the vertical section. The development of soil profile starts with the fracturing of bed rock due to physical weathering. Water, oxygen CO2 etc. penetrates into rock fractures and cause chemical weathering. This weathered material increases in volume called soil if not removed by the process of erosion. This process continues until the whole rock is exhausted.
Soil profile is consists primarily of three horizons as follows :-
Top soil : It is top most layer and has the highest organic matter proportion. It is the region of highest biological activities. In this horizon minerals are generally dissolved in the fresh water and removed as solution phase. Some part of fine particles can also be removed.
Sub soil : The B -horizon or Sub soil is the layer where mineral and clay particles accumulates. It is comparatively lighter in color and holds water in it. This is less organic in nature.
C-horizon : It lies where the partially altered bedrock occurs. In this layer pieces of original rock present and can be identified
- O (Organic / humus) : Mostly organic matter such as decomposing leaves. It’s thickness can vary and not necessarily found in all soil profile.
- A (Top soil) : Mostly mineral from parent rock with organic matter. Best for the floral growth.
- E (Eluviated) : Leached clay mineral and organic matter leaving a concentration of sand and silt particles of quartz or other resistant materials. May not be present in older soils and forest soils.
- B (Sub soil) : Rich in mineral that is leached from A to E horizons and accumulate here.
- C (Parent material) : The broken parent rock material from which soil develops.
- R (Bedrock) : A fresh mass of rock like granite, basalt, sandstone, limestone etc. It is not part of soil.
- Few important terminologies
- Catena : It is a sequence of soils from hilltop to valley floor.
- Grus : Grus is an ill-defined product of deep weathering of coarse grained rocks whose relationship to other weathering changes remains unclear.
- Solum : It is consists of Top soil and Sub soil layers that have undergone same weathering conditions. Base of Solum is C-horizon.
- Saprolite : Any layer devoid of any organic matter and made up of broken bed rock is called Saprolite or C-horizon.
Climatic soil Classification :- Click here
Indian soil Classification :- Click here
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