iluwacji

Iluwacja, or illuviation, is a soil science term describing the downward movement of materials from upper soil horizons and their deposition in a lower horizon. It operates as a counterpart to eluviation, the withdrawal of materials from higher horizons by percolating water. Illuviation leads to the formation of an illuvial horizon in which the deposited substances accumulate.

Materials commonly transported downward include clay minerals, organic matter, and iron and aluminum oxides. In many soils this accumulation creates a distinct B horizon, often labeled Bt to indicate clay illuviation. Other illuvial horizons can be identified as Bh for humus illuviation or Bhs for combined humus and oxide illuviation, depending on the soil classification system used. The precise mineral and organic components deposited vary with climate, drainage, and parent material.

Illuviation depends on sufficient leaching by moving water, which is more pronounced in humid or well-drained conditions. Climate, soil texture, structure, and drainage control the rate and extent of illuviation. It is typically most evident in temperate and tropical soils where rainfall is ample.

In soil classification and genesis studies, illuviation helps explain horizon development and color, texture, and structure changes in soils. Recognizing illuviation aids in distinguishing soil orders and suborders and informs interpretations of soil fertility and land-use suitability, as well as the long-term evolution of soil profiles.