The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the fourth edition 2022. It is edited by a working group of the International Union of Soil Sciences (IUSS).
thumb|WRB, 4th edition (2022)
Background
History
Since the 19th century, several countries developed national soil classification systems. During the 20th century, the need for an international soil classification system became more and more obvious.
From 1971 to 1981, the Food and Agriculture Organization (FAO) and UNESCO published the Soil Map of the World, 10 volumes, scale 1 : 5 M). The Legend for this map, published in 1974 under the leadership of Rudi Dudal, became the FAO soil classification. Many ideas from national soil classification systems were brought together in this worldwide-applicable system, among them the idea of diagnostic horizons as established in the '7th approximation to the USDA soil taxonomy' from 1960. The next step was the Revised Legend of the Soil Map of the World, published in 1988.
In 1982, the International Soil Science Society (ISSS; now: International Union of Soil Sciences, IUSS) established a working group named International Reference Base for Soil Classification (IRB). Chair of this working group was . Its mandate was to develop an international soil classification system that should better consider soil-forming processes than the FAO soil classification. Drafts were presented in 1982 and 1990.
In 1992, the IRB working group decided to develop a new system named World Reference Base for Soil Resources (WRB) that should further develop the Revised Legend of the FAO soil classification and include some ideas of the more systematic IRB approach. Otto Spaargaren (International Soil Reference and Information Centre) and Freddy Nachtergaele (FAO) were nominated to prepare a draft. This draft was presented at the 15th World Congress of Soil Science in Acapulco in 1994. At the same congress, the WRB was established as an ISSS working group replacing the IRB. At the 16th World Congress of Soil Science in Montpellier in 1998, the first edition of the WRB was published. At the same congress, the ISSS endorsed the WRB as its correlation system for soil classification. (In 2014, the USDA soil taxonomy also received the status of a correlation system.) At the 18th World Congress of Soil Science in Philadelphia in 2006, the second edition of the WRB was presented, and at the 20th World Congress of Soil Science in Jeju in 2014, the third edition. An update of the third edition was issued in 2015. Whereas the second edition was only suitable for naming soils, the third and the following edition can additionally be used for creating map legends. At the 22nd World Congress of Soil Science in Glasgow in 2022, the fourth edition was published. The 4th edition is an open access document under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
The WRB has two hierarchical levels (see below) and has in that sense a similar approach as the French référencial pédologique (1992, 1995, 2008). Contrary to that, the USDA soil taxonomy is strongly hierarchical and has six levels. The classification in WRB is based mainly on soil morphology (field and laboratory data) as an expression of pedogenesis. Another difference with USDA soil taxonomy is that soil climate is regarded only as a soil-forming factor and not as a soil characteristic. The WRB is not meant to replace national soil classification systems, which, for their area, may be more detailed than the WRB.
WRB Working Group
The WRB is edited by a working group of the International Union of Soil Sciences (IUSS). The current chair of the working group is Cezary Kabala (Wroclaw University of Environmental and Life Sciences, Poland, since 2022). The current vice-chair is Stephan Mantel (International Soil Reference and Information Centre (ISRIC), The Netherlands, since 2018).
Chairs of the WRB working group and responsible first authors of the WRB editions are: Seppe Deckers (Belgium, 1st edition 1998), Erika Michéli (Hungary, 2nd edition 2006) and Peter Schad (Germany, 3rd edition 2014 and 4th edition 2022). that is currently hosted by the ISRIC. It provides the following:
- the currently valid fourth edition of the WRB (2022) for download,
- the third edition (Update 2015) with the English original and the translations into Czech, French, Georgian, Polish, Russian, Slovene, and Spanish,
- an explanation of the system,
- soil profile photos of all RSGs, which may be downloaded and used if the author is accredited (additional photos can be found on the World of Soils page of the IUSS),
- the history of the WRB,
- the WRB leadership,
- information about past and upcoming workshops,
- teaching material (including videos),
- invitations for publications,
- links to other institutions important for the WRB.
The WRB 2022
Architecture
The classification is based on diagnostic horizons, diagnostic properties and diagnostic materials, altogether called diagnostics: