podzol

PODZOL, also spelled PODSOL, also called PODZOL SOIL, or PODSOL SOIL, typically forms in very cold climates under coniferous forests, heaths, or tundra. The humus that is formed is very rich in slightly polymerized substances (e.g., fulvic acid), which descend through the soil, form complexes with the clay minerals and iron, and leach out all the weathering products--i.e., bases, iron, alumina (aluminum oxide), and silica (silicon dioxide).

Podzols are characterized by one or more of the following horizons (layers): a bleached horizon that resembles ash; a spodic horizon, one formed by the accumulation (illuviation) of clay or organic matter, or both, which is transported by water and which, because it is rich in amorphous clay (allophane), iron, and organic matter, has a high cation-exchange capacity (ability of a charged metal atom in the structure to exchange places with another in aqueous solution); a horizon in which the soil grains are coated with organic matter and bound together; and hard horizons (pans) cemented together by organic matter or iron and resistant to breakdown in water.