The fourth edition 2022 is the currently valid WRB.
The correct citation is:
IUSS Working Group WRB. 2022. World Reference Base for Soil Resources. International soil classification system for naming soils and creating legends for soil maps. 4th edition. International Union of Soil Sciences (IUSS), Vienna, Austria.
The lead author of the fourth edition is Peter Schad (Technical University of Munich, Germany). The fundamental decisions have been made by the members of the WRB Board: Lúcia Anjos (Brazil), Jaume Boixadera Llobet (Spain), Seppe Deckers (Belgium), Stefaan Dondeyne (Belgium), Einar Eberhardt (Germany), Maria Gerasimova (Russia), Ben Harms (Australia), Cezary Kabała (Poland), Stephan Mantel (The Netherlands), Erika Michéli (Hungary), Curtis Monger (USA), Rosa Poch Claret (Spain), Peter Schad (Germany), Karl Stahr (Germany), Cornie van Huyssteen (South Africa). Vincent Buness (Germany) and Margaretha Rau (Germany) served as secretaries of the WRB Board.
The fourth edition comprises 13 Chapters:
- Background and basics
- The rules for naming soils and creating legends for soil maps
- Diagnostic horizons, properties and materials
- Key to the Reference Soil Groups with lists of principal and supplementary qualifiers
- Definitions of qualifiers
- Codes for the Reference Soil Groups, qualifiers and specifiers
- Annex 1: Field Guide
- Annex 2: Summary of analytical procedures for soil characterization
- Annex 3: Horizon and layer designations
- Annex 4: Soil description sheet
- Annex 5: Guidance on database set-up
- Annex 6: Colour symbols for RSG maps
Annex 1 and 3 replace the FAO Guidelines for Soil Description (2006).
The definitions in the WRB are based on field and laboratory data. The field data are according to Annex 1. The methods to obtain the laboratory data are listed in Annex 2 and described in the Procedures for Soil Analysis (Van Reeuwijk 2002). The latter are published by the International Soil Reference and Information Centre (ISRIC).