What is illuviation and in which layer does this process primarily occur?
Illuviation is the movement of particles in the soil to another layer.
Illuviation occurs when water moves through the soil. It moves small particles of clay, iron, humus, calcium carbonate, and other minerals with it. These particles are deposited in the subsoil or in zones just beneath the surface.
These areas are known as illuvial zones. The material moved is called the illuvium.