Soil profile and horizons

What is soil profile?

Generally soil  is found in layers, these layers are arranged in a definite pattern during soil formation, this sequence of the soil layers is called soil profile.
These particular layers of soil profile are called horizons. The main layers are top  soil, sub soil and parental rock.

Horizons

Horizons are those layers in which the soil is arranged  and form soil profile during its formation. There are basically five such horizons named as  O horizon, A horizon, B horizon, C horizon and R horizon.  These horizons are seperately described here :- 

•  Horizon O-  This is an organic horizon , so named O horizon . It is mainly composed of partially decomposed organic matter.

This horizon is again composed of two regions O1 region and O2 region.

O1 region- This region is uppermost layer and mainle consists freshly fallen dead leaves and animals. Prior to they undergoes decomposition.

O2  region- This is the second region under the O1 region and consists of newly dcomposed dead remains of plants and animals. In O2 region decomposition has just begun.

• Horizon A -  This is the ZONE OF ELUVIATION. It is also known as top soil, this is the mineral horizon rich in silica and contains rich amount of organic matter. A horizon is generally having dark colour this dark colour is due to the presence of humus which  mixes with weathered minerals, Which also helps to identify this horizon characterstically.

• Hoirzon B-   B horizon is commonly known as  Sub soil. Sequencely this horizon is present below the O and A horizon and chiefly consists large amount of  clay , silicate and aluminium. I is also known as the ZONE OF ILLUVIATION because the minerals accumulates in this region. The roots of big trees ends up in this region. It is lighter in colour i.e., reddish brown , as compare to the above layer. This layer is located below the A horizon and above the C layer thus intermediate between these two layers, i.e., Horizon A and horizon C.

• Horizon C - It does not contains any organic material and is an inorganic layer. I helps in locking all the properties of the above layer that we studied above.. It contains weathered rock and sediments that is formed during the soil formation. The C horizon is located below the C horizon. The depth of this layer is very deep this can be noticed by the fact that only one layer is present below this layer that is Horizon R. Roots of trees are reached till this layer.

• Horizon R - It is the  lowermost layer that is found below the C horizon and consists mainly unweathered parent material. It is a bed rock, as only parental materials are present in this layer no soil is present here in this layer. Many few roots are present in this layer as it is not very easily possible to reach in this region. This is the last layer out of the all five layers, roots of many plants cannot reach to this layer, there is hardly any plants or trees whose roots reach to this layer, because this is the last layer of soil and it is difficult to dug up to this layer.

So these were the major description of horizons which makes up the soil profile and all this process of arrangement of soil horizons is known as soil formation, during which the soil horizons or layers are arranged in the correct sequence to make up the soil profile.