SOIL PROFILE — AGRICULTURE OPTIONAL
This blog is for Agriculture Optional, M.Sc Entrance, AFO, IFFCO, JRF, NABARD, RRB-SO, and STATE Exam.
The vertical section of the soil showing the various layers from the surface to the unaffected parent material is known as a soil profile.
The various layers are known as horizons. A soil profile contains horizons O, A, B, C and R horizons and all the possible sub-horizons.
O horizon
It is called an organic horizon. It is formed in the upper part of the mineral soil, dominated by fresh or partly decomposed organic materials.
— If the mineral fraction has > 50% clay, then OM is > 30 %
— If the mineral fraction has < 50% clay, then OM is > 20 %
The organic horizons are commonly seen in forest areas and generally absent in grassland, cultivated soils.
Such O horizon is visible in virgin soil and absent in Arable soils.
A horizon
The horizon of organic matter accumulates adjacent to the surface and has lost clay, iron and aluminium. It is a zone of washing out/maximum leaching.
B horizon
The horizon of maximum Illuviation. Horizon in which the dominant features are an accumulation of clay, iron, aluminium or humus alone or in combination.
C horizon
It is the horizon below the solum (A + B), relatively less affected by soil-forming processes. It is outside the zone of major biological activity. It may contain an accumulation of carbonates or sulphates, calcium and magnesium.
R
Underlying consolidated bedrock and may or may not be like the parent rock from which the solum is formed.
