What is the process called where fine soil particles are washed down into subsoil?

The correct term for the process where fine soil particles are washed down into subsoil is called illuviation. This process occurs when soluble or suspended materials are leached from the upper layers of soil, particularly the topsoil, and deposited into the subsoil layer. Illuviation is a critical part of soil formation and is often associated with the movement of nutrients, minerals, and organic matter within different soil horizons.

Illuviation is distinct from other processes; for example, erosion refers to the general removal of soil and rock from one location and its movement to another, which may not necessarily imply the deposition of fine particles into subsoil. Alluviation specifically describes the deposition of sediment from water across floodplains or river beds, and salivation is not a recognized process in soil science. Understanding these definitions helps clarify the unique role that illuviation plays in nutrient cycling and soil development, reinforcing its importance in ecological and agricultural context.