The processes of eluviation and illuviation are the main forces in soil horizonation and give rise to the many layers of soil you see in a soil profile. The two processes combine to create a natural filtration system that changes soil at every level.
Eluviation
Eluviation is defined as the moving of dissolved or suspended substances away from the higher layers of the soil by rainwater that moves downward.
It occurs in the A horizon and E horizon of the soil.
- What is being washed away: Clay-sized particles, organic matter, iron, aluminum, etc.
- The result: There is coarse and light-colored soil left in the upper part of the soil.
Illuviation
Illuviation is defined as accumulation of the washed material in the lower part of the soil. Water deposits substances as it slows at a certain layer.
- Where this happens: Mostly in the B horizon.
- What is being accumulated: The clay and humus transported downward.
- The result: This layer becomes dense and heavy in clay.
The role of climate
These processes depend highly on water. Water is a vital factor.
- Humid climate: Huge rainfall leads to very heavy processes of eluviation and illuviation.
- Dry climate: There is very little rainfall, and therefore, there is no significant soil horizon formation.
Readings:
Processes of Soil Formation
Factors Affecting Process of Soil Formation
What is Soil?: Definition, Composition, Types and Functions
