Soil profile

Soil profile refers to the vertical arrangement /section through the soil from the surface up to the parent rock. It is composed of soil layers referred to as horizons which are differentiated in terms of color and texture.

Soil profiles differ from place to place however an ideal soil profile is composed of horizons A.B, C and D as shown below.

Horizon A.

• It’s the topmost layer sometimes referred to as the top soil
• The top designated as A₀₀ consists of un-decomposed litter of dead leaves and
• It’s followed by A₀ which is decomposing organic matter and A₁ which has high humus content and which gives this horizon its dark
• It’s followed by A₂ which is poor in nutrients because of the effect of leaching (removal to solution of nutrients) and eluviation (movement of material /clay particles in suspension) and which make it light coloured /bleached. It’s followed by a transition

Horizon B.

• It’s the soil layer below horizon A and it’s the zone where nutrients and materials removed from horizon A accumulate in a process known as illuviation (in washing of materials).
• It’s therefore often richer in nutrients than the zone above it, and may be darker in in colour
• It’s sometimes characterized by a hard pan caused by the accumulation of large quantities of clay and other nutrients.

Horizon C

Consists of recently/partially weathered parent material (regolith) resting on the bed rock.

Horizon D

It’s the last layer of the profile and consists of solid parent rock or bedrock.