In pedology, leaching is the loss of mineral and organic solutes due to very heavy rainfall, high temperature and percolation. It is a mechanism of soil formation distinct from the soil forming process of eluviation, which is the loss of mineral and organic colloids. Leached and elluviated materials tend to be lost from topsoil and deposited in subsoil. A soil horizon accumulating leached and eluviated materials is referred to as a zone of illuviation.
Laterite soil, which develops in regions with high temperature and heavy rainfall, is an example of this process in action.