World’s Soil Resources

PLANOSOLS (Albaqualfs, Albaquults and Argialbolls)
Planosols are seasonally water-saturated or flooded, poor acid soils with bleached, generally silty surface
horizons with an abrupt transition to a dense subsoil with significantly more clay (Figure A 14). There may be
pore infillings of bleached material in the subsoil. Clay destruction and aluminium interlayering driven by
periodic iron hydroxide reduction and reoxidation (ferrolysis) has been recognised as a process sometimes
involved in the formation of the silty surface horizons (Brinkman, 1979; Van Ranst et al., 2011).
Planosols occur in generally level areas in climates with contrasting wet and dry seasons, mainly in the
subtropics but in temperate areas and the tropics as well. Their total extent is estimated at 1.3 million km 2 .
They are extensive in Latin America (southern Brazil, Paraguay, and Argentina) and Australia, and they also
occur in Africa (Sahelian zone, East and southern Africa), the eastern United States, Siberia, China, and
Southeast Asia (Bangladesh, Thailand).
Natural vegetation on Planosols is sparse grass with or without shrubs or small trees; extreme Planosols
may be barren. They are generally used for grazing or for grain or root crops in temperate areas. In the
subtropics and tropics, rainfed paddy (wetland) rice is grown on bunded fields; with irrigation, they can be
double cropped with a second paddy rice or dryland crop. Yields are very low without fertilizers and remain
sub-optimal even with fertilizers because of the poor physical and chemical soil conditions.
Status of the World’s Soil Resources | Main Report Annex | Soil groups, characteristics,
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distribution and ecosystem services