World Reference Base for Soil Resources
The World Reference Base for Soil Resources (WRB) is the international standard taxonomic soil classification system endorsed by the International Union of Soil Sciences (IUSS). It was developed by an international collaboration coordinated by the International Soil Reference and Information Centre (ISRIC) and sponsored by the IUSS and the FAO via its Land & Water Development division. It replaces the previous FAO soil classification.
The WRB borrows heavily from modern soil classification concepts, including USDA soil taxonomy, the legend for the FAO Soil Map of the World 1988, the Référentiel Pédologique and Russian concepts. The classification is based mainly on soil morphology as an expression pedogenesis. A major difference with USDA soil taxonomy is that soil climate is not part of the system, except insofar as climate influences soil profile characteristics. As far as possible, diagnostic criteria match those of existing systems, so that correlation with national and previous international systems is as straightforward as possible.
The WRB is meant for correlation of national and local systems. The level of detail corresponds to USDA soil taxonomy subgroups, without the soil climate information. It is not detailed enough for mapping at scales larger than about 1:200k, although proposal have been made to couple WRB with substrate information to map at 1:50k in regional studies.
Identification key to the 32 reference soil groups:
|1.||Soils with thick organic layers:||Histosols (HS)|
|2.||Soils with strong human influence|
|Soils with long and intensive agricultural use:||Anthrosols (AT)|
|Soils containing many artefacts:||Technosols (TC)|
|3.||Soils with limited rooting due to shallow permafrost or stoniness|
|Ice-affected soils:||Cryosols (CR)|
|Shallow or extremely gravelly soils:||Leptosols (LP)|
|4.||Soils influenced by water|
|Alternating wet-dry conditions, rich in swelling clays:||Vertisols (VR)|
|Floodplains, tidal marshes:||Fluvisols (FL)|
|Alkaline soils:||Solonetz (SN)|
|Salt enrichment upon evaporation:||Solonchaks (SC)|
|Groundwater affected soils:||Gleysols (GL)|
|5.||Soils set by Fe/Al chemistry|
|Allophanes or Al-humus complexes:||Andosols (AN)|
|Cheluviation and chilluviation:||Podzols (PZ)|
|Accumulation of Fe under hydromorphic conditions:||Plinthosols (PT)|
|Low-activity clay, P fixation, strongly structured:||Nitisols (NT)|
|Dominance of kaolinite and sesquioxides:||Ferralsols (FR)|
|6.||Soils with stagnating water|
|Abrupt textural discontinuity:||Planosols (PL)|
|Structural or moderate textural discontinuity:||Stagnosols (ST)|
|7.||Accumulation of organic matter, high base status|
|Typically mollic:||Chernozems (CH)|
|Transition to drier climate:||Kastanozems (KS)|
|Transition to more humid climate:||Phaeozems (PH)|
|8.||Accumulation of less soluble salts or non-saline substances|
|Calcium carbonate:||Calcisols (CL)|
|9.||Soils with a clay-enriched subsoil|
|Albeluvic tonguing:||Albeluvisols (AB)|
|Low base status, high-activity clay:||Alisols (AL)|
|Low base status, low-activity clay:||Acrisols (AC)|
|High base status, high-activity clay:||Luvisols (LV)|
|High base status, low-activity clay:||Lixisols (LX)|
|10.||Relatively young soils or soils with little or no profile development|
|With an acidic dark topsoil:||Umbrisols (UM)|
|Sandy soils:||Arenosols (AR)|
|Moderately developed soils:||Cambisols (CM)|
|Soils with no significant profile development:||Regosols (RG)|
WRB soil groups 
|Code||Soil type||Brief description|
|AC||Acrisol||Red, brown or yellow coloured soil, develops in areas of intense weathering, has a clay rich B horizon|
|AN||Andosol||Soil developed from volcanic material, are young immature soils, characteristics depend on type of volcanic material|
|AR||Arenosol||Sandy soil with no more profile development than an A horizon|
|CL||Calcisol||Soil with a substantial secondary accumulation of lime|
|CM||Cambisol||Transformation of soil matter (Fe particularly) in situ without moving in profile. Mostly brownish color.|
|CH||Chernozem||Fertile black-coloured soil containing a high percentage of humus, phosphoric acids, phosphorus and ammonia|
|CR||Cryosol||Soil in permafrost areas, exhibits cryoturbation and is usually rich in organic matter|
|DU||Durisol||Soil of some arid and semi-arid environments, contains cemented secondary silica|
|FR||Ferralsol||Red to yellow soil rich in iron and aluminium, common in temperate to tropical humid areas|
|FL||Fluvisol||Soil developed above flood plain sediments, A horizon is commonly directly above C horizon|
|HS||Histosol||Soil consisting primarily of organic materials, common in wetlands|
|LP||Leptosol||Shallow soil over bedrock, calcareous material or a deeper soil that is gravelly or stony, common in mountains|
|PZ||Podzol||Soil that presents significant podzolization, common in coniferous forests|
|UM||Umbrisol||Soil with a dark topsoil and in which organic matter has accumulated significantly within the mineral surface soil|
|VR||Vertisol||Shows significant and recurrent swelling with water, high content of expansive clay|
- IUSS Working Group WRB. 2006. World reference base for soil resources 2006. 2nd edition. World Soil Resources Reports No. 103. FAO, Rome. ISBN 92-5-105511-4, http://www.fao.org/ag/agl/agll/wrb/doc/wrb2006final.pdf
- Bridges, E. M. (1997). World soils (3rd ed.). Cambridge: Cambridge University Press.
- Bridges, E. M., Batjes, N. H., & Nachtergaele, F. O. (Eds.). (1998). World Reference Base for soil resources: atlas. Leuven: ACCO.
- Deckers, J. A., Nachtergaele, F. O., & Spaargaren, O. C. (Eds.). (1998). World Reference Base for soil resources: introduction. Leuven: ACCO.
- Driessen, P., Deckers, J., Spaargaren, O., & Nachtergaele, F. (Eds.). (2001). Lecture notes on the major soils of the world. Rome: FAO.
- FAO. (1998). World Reference Base for Soil Resources. Rome: Food and Agriculture Organization of the United Nations.
- Jahn, R., Joisten, H., & Kabala, C. (2004). The “Reference Soil Series” Concept of the First European Joint Soil Map at a Scale of 1:50 000, Sheet Zittau – a Framework to Upgrade the Information Content of Lower Level WRB Units. Paper presented at the EUROSOIL 2004, Freiburg im Breisgau (D).
- World Reference Base for Soil Resources (WRB) 2006 The latest WRB classification manual
- ISRIC Lecture notes on the Major Soils of the World. 2001.(with maps showing their distribution, soil profiles)
- WRB home page at the FAO
- WRB links at the Compendium of On-line Soil Survey Information
|Wikimedia Commons has media related to: World Reference Base for Soil Resources|