11. Podzol Soils

Podzol Soils are formed in association with podocarp and beech forests in areas with good drainage and rainfall ≥~1200 mm yr⁻¹, which provides an environment of acid leaching. Podzol Soils cover 13% of New Zealand and are most widespread on the South Island West Coast, the high country of the North Island, and in Northland. Distinctive Perch-gley Podzol Soils occur under high rainfall on the South Island West Coast. The Podzol’s most distinctive feature is a pale grey, or white, E horizon beneath the topsoil. The E horizon is pale because iron, aluminium, and silicon-bearing materials, and organic compounds, have been moved downwards and redeposited beneath the E horizon as dark-coloured podzolic-B horizons. The podzolic-B horizons usually comprise an organic-rich (Bh) horizon over a reddish iron-mineral-rich (Bs) horizon. Podzol Soils are defined by the podzolic-B horizon or a humus- or ortstein-pan. Podzols are extremely acidic with pH often as low as 4. The acidity, and E-Bh-Bs horizonation, are caused by acidified rainwater seeping downwards, mobilising and leaching or translocating organic materials, iron, aluminium, and silicon compounds, and other nutrients down the profile. Enlerached materials subsequently accumulate in lower horizons where increased pH, and microbial activity, support adsorption, and precipitation.