Soil Profile Descriptions

   Hello everyone, through this post I'm trying to give an inside story about Soil Profile. Hope you guys will enjoy it.

Soil Profile: 

   It may be defined as the section through a soil extented from the soil surface to the parent rock material.

   Soil profile is divided into 5 horizons,

• O
• A
• B
• C 
• E and these 5 common horizons are called as Master Horizons.

O Horizon: 

   The 'O' group refers to the organic horizon made of decayed plants & animals. This horizon is found mostly in the forest areas. It is divided into 2 specific horizons:

• OL1- 1st layer of organic horizon where the original form of plants & animals can be easily reconized by the naked eye.
• OL2- a specific layer of organic horizon where the original form of plants & animals cannot be recognized.

A Horizon:

   Present at or near the surface & characterized as zones of 'washing out' or maximum leaching. It can be divided into 3 specific horizon:

• A1- uppermost mineral soil horizon rich in organic matter & darker in colour as compared to the lower horizons.
• A2- horizon of washing out or eluviation of clay, sesquioxides(Fe, Al) & corresponding accumulation of resistant minerals(quartz). Lighter in colour compared to A1.
• A3- transition horizon between A & B horizons with properties more alike A1 or A2 that of B.

B Horizon:

   Horizons of 'washing in' or accumulation of eluviated minerals from above horizons & even from the below horizons as CaCO3, CaSO4 & other salts due to evaporation(arid conditions). 3 types of specific horizons:

• B1- transition horizon between A & B but properties more alike B than that of A.
• B2- zone of maximum accumulation of clay & hydrous oxides; organic content more compared to A2 horizon.
• B3- transition horizon between B & C but properties more alike B than that of C.

C Horizon:

   Unconsolidated material underlying the solum(A + B). It may or may not be the same as parent material of solum; outside the zone of major biological activities; affected very little by the solum forming process.

Solum: 

   Surface and sub-soil layers that have undergone some soil forming processes (A+B horizons). The base of the solum is relatively unweathered parent material. It doesn't have any maximum or minimum thickness.

Regolith:

   The layer of rock & mineral fragments that rest on the bed rock & is produced by weathering of rocks (A+B+C horizon); includes all the weathered material within the profile. It has 2 components :

• Most weathered solum,
• Least weathered saprolite- lies above bed rock but beneath the regolith.

Reference:

       Introductory Soil Science( fourth edition), D. K. Das, Kalyani Publishers, 2015.