illuviated

Illuviated is an adjective used in soil science to describe a horizon that has received and accumulated materials through the process of illuviation. Illuviation is the downward movement of dissolved or suspended substances by percolating water, resulting in an illuvial horizon enriched relative to the material that lies above it. Common illuvated constituents include clay minerals, iron and aluminum oxides, and sometimes organic matter or carbonates.

The term comes from Latin roots meaning to wash in or to wash into, and it is distinguished from eluviation, the process of materials being removed from a horizon by water. In soils where illuviation is active, the lower horizon often displays higher clay content and distinct mineralogical or color changes compared with the upper horizon.

In practice, illuviated horizons are frequently referred to as Bt horizons or argillic horizons in many soil classifications. The accumulation of clay and other constituents can alter soil texture, color, structure, and permeability, and it is a key indicator of soil-forming processes and drainage conditions. Illuviation, together with eluviation, shapes the vertical differentiation of soils and helps classify soils such as Alfisols and Ultisols, among others.

See also: eluviation, argillic horizon, pedogenesis, soil horizon, Alfisols, Ultisols.