Soil profile

Soil profile

Soil profile is the vertical cross section of layers (horizons) from top to bottom. The soil profile shows layers in different stages of development.

Each layer differs from the others in colour, structure, thickness, composition etc.

The typical soil profile is easily distinguishable into four (4) layers or horizons. i.e. A,  B, C, D.

Diagram showing the soil profile

Horizon A

  • It is also called zone of eluviation where soluble nutrients are washed and deposited to the lower layers.
  • It contains adequate plant nutrients.
  • It contains high amounts of humus (organic matter)
  • It is loose and facilitates easy penetration of plant roots.
  • It is well aerated
  • It is dark in colour due to the high amount of humus.
  • It has more active living organisms.

Horizon B

  • It is called the illuviation zone since it is where nutrients from top soil accumulate or get deposited.
  • It contains less living organisms.
  • It has more compacted soils.
  • It is light brown or reddish yellow in colour.
  • A hard pan may be formed which is an impermeable layer below the top soil that resists water movement.
  • It resists root penetration.

Horizon C

  • It consists of parent materials that have just started undergoing weathering.
  • It is a very compacted layer.
  • It  does not contain humus
  • It does not contain living organisms
  • It is poorly aerated
  • Plant roots cannot penetrate easily through it.

Horizon D

  • It is called horizon of un
  • weathered rocks
  • Under ground water may accumulate on top of the bedrock to form ponds.
  • Trees with excessively deep roots can obtain water from this horizon.

The soil profile may be described as:

  • Mature: when it has clear horizons.
  • Trancated: when the horizons are not clear due to erosion.

Influence of soil profile on crop production

Soil profile influences nutrient availability.

Soil profile influences soil aeration.

It influences the water holding capacity of the soil.

It influences the drainage of the soil.

It influences availability of soil living organisms which break down organic matter.