THE 4 HORIZONS OF SOIL PROFILE

THE 4 HORIZONS OF SOIL PROFILE




Soil profile refers to the vertical arrangement of the various soil layers from the top layer down to the parent rock or bottom layer.

It is a vertical section through the soil horizons extending into the parent material or the bedrock.

It describes the sections downwards through the soil which comprises differing characteristics in terms of texture, color, mineral composition, the ratio of the combination of organic and inorganic matter, hardness, and rate of weathering.




The different layers are referred to as horizons.

A soil horizon is a well-defined layer within the soil profile parallel to the local round surface. There are four main horizons namely:

A horizon, B horizon, C horizon, and D horizon. Each horizon has different physical and chemical properties, which result from various soil-forming processes such as weathering, the introduction of humus, and the movement of minerals.

O-HORIZON

This is the topmost/ surface layer of the soil comprising organic matter.




The constituents of this layer include un-decomposed litter, decomposing organic matter, and humus.  

A-HORIZON

This is also known as the topsoil and it is rich in organic matter which organic matter accounts for dark colour.

Leaching and Eluviation may at times impoverish the topsoil.  




B-HORIZON

This is known as subsoil. Nutrients removed from the A horizon through leaching and Eluviation accumulate or are deposited in this horizon.

The process of plant nutrients precipitating or accumulating in this horizon is known as illuviation.

This horizon may also be characterized by hardpans due to the accumulation of large quantities of clay and other nutrients.  

C-HORIZON




This consists of partially weathered rock, this is because weathering and other soil-forming processes may not effectively operate at this depth.

D-HORIZON

This consists of solid parent rock or unweathered rock or fresh parent material. It is also known as the bedrock.

It has no soil particles but has potential for future soil formation




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