Podsolization

Podsolization, or podzolization, is a pedogenic process in which highly leached, acidic soils remove soluble bases and silicate minerals from the upper horizons and accumulate iron and aluminum oxides and humus in a lower horizon. This translocation creates a characteristic sequence of eluviated and illuviated horizons. The upper eluviated layer, an E horizon, is pale in color due to depletion of iron and organic matter, while the lower illuvial horizon, often called a spodic horizon, concentrates organic matter with iron and aluminum oxides, and is commonly labeled Bh, Bhs, or Bs depending on composition.

Chemical mechanism involves organic acids from litter and humification processes mobilizing aluminum and iron, as well as silica. Rainfall and acid precipitation promote leaching, and base cations such as calcium, magnesium, potassium, and sodium are removed, sustaining acidic conditions that promote further translocation of materials.

Podsolization occurs most readily in cool, humid climates with well-drained sandy or acidic parent materials, especially under coniferous or mixed forests. Soils showing this process are typically podzols or spodosols in temperate to boreal regions and are less common in arid or highly weathered tropical soils. The process is a major diagnostic feature in soil classification and helps explain distinctive soil color and fertility patterns, as well as associated vegetation and habitat characteristics.