Podzols

• Definition

• Further description

• General environment

• Global extent and location

• Land use

• Main production constraints

• Summary

Definition

Podzols are soils characterized by the presence of a spodic horizon containing an accumulation of organic matter, iron and aluminium within 200 cm of the soil surface.  The process of translocation and accumulation is usually shown by the occurrence of an albic horizon underlain by the spodic horizon.

Further description

A cover layer of acid organic litter (under the original vegetation) is followed by a marked bleached (albic) horizon due to the leaching out of iron, aluminium and humus. Strong leaching, with highly acidic conditions, provide conditions where a mor humus develops and clay minerals are broken down.  In association with the organic breakdown products, iron and aluminium are transported from the eluvial horizons to the spodic horizon.

General environment

Podzols develop on sandy substrates and are soils of the northern cool temperate areas with coniferous forests. Podzols may also occur in many parts of the tropics where they develop in deposits of almost pure quartz sand (see sandy soils).

Global extent and location

Podzols cover an estimated 487 million hectares  worldwide (see table), mainly in the temperate and boreal regions of the northern hemisphere (see figure).  Tropical Podzols total not more than 32 million hectares, important occurrences are along the Rio Negro and in the Guyanas of South America, in the Malesian region (Kalimantan, Sumatra, Irian) and in northern Australia.  There, they mainly occur in residual sandstone weathering in perhumid regions and in old, alluvial quartz sands.

Land use

Low nutrient status, sandy texture and low pH value make Podzols infertile soils.  Therefore the agricultural use of Podzols is limited.  They are normally reserved for coniferous forestry, low intensity grazing or are left fallow.  However, if fertilizers, liming and irrigation are practised reasonable yields of arable crops may be achieved.

Main production constraints

Podzols are very sandy, acid and nutrient deficient.  Aluminium toxicity, restriction of nitrification and phosphorus deficiency are major problems encountered when growing crops on Podzols.  Furthermore, the leaching out of iron and subsequent accumulation in lower horizons may lead to a thin iron pan which is impervious.  They may then have hydromorphic properties.  Podzols are inherently infertile for arable crops.  Before crops can be grown, these soils must be limed, fertilized and cultivated;  if formed the iron pan must be broken to improve their drainage.  Then Podzols can be productive, provided that constant additions of lime and fertilizers are applied.

Summary

Podzols are the principal soils of the northern coniferous forest.  They have an extremely low potential for agriculture since they need heavy applications of lime and fertilizers but they have proved to be productive in some parts of Europe and North America if the respective inputs are applied.  They are often used for coniferous forest or low volume grazing.