World Reference Base for Soil Resources
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).
[2] The Legend for this map, published in 1974 under the leadership of Rudi Dudal, became the FAO soil classification.
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.
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).
The classification in WRB is based mainly on soil morphology (field and laboratory data) as an expression of pedogenesis.
The WRB is edited by a working group[4] 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).
[1] In a defined sequence, the key asks for the presence or absence of certain diagnostics in a certain depth range.
In addition, the key asks for single characteristics, e. g., a certain clay content or a certain base saturation.
Qualifiers may be combined with specifiers (e. g. Epi-, Proto-) to form subqualifiers (e. g. Epiarenic, Protocalcic).
The depth-related specifiers referring to layers are of special importance, although their use is optional: The number of qualifiers used in a map legend depends on the scale.
Depending on the purpose of the map or according to national traditions, at any scale level, elective qualifiers may be added.
For this purpose, WRB uses the following nomenclature: Soils representing smaller areas are ignored in the denomination of the map unit.
For codominant and associated soils, it is allowed to use less principal qualifiers than would correspondent to the used map scale level.
From the list of the supplementary qualifiers, Siltic (silty from 0 to 60 cm), Loamic (loamy from 60 cm downwards), Aric (ploughed), Cutanic (clay coatings), Differentic (the clay migration led to a significant difference in clay content), Endic (the argic horizon starts below 50 cm) and Ochric (relatively small concentrations of organic carbon) apply.
Bringing the supplementary qualifiers into the correct order (first the textural qualifiers from the top to the bottom of the soil profile, then all others in alphabetical order), the soil is an Albic Stagnic Luvisol (Siltic, Loamic, Aric, Cutanic, Differentic, Endic, Ochric).
Now, the soil name is: Amphialbic Endostagnic Luvisol (Anosiltic, Endoloamic, Aric, Cutanic, Differentic Endic, Ochric).
Let's say that our example soil Amphialbic Endostagnic Luvisol (Anosiltic, Endoloamic, Aric, Cutanic, Endic, Ochric) covers 60% of the area of a map unit.
