World Reference Base for Soil Resources (WRB)

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 ISRIC–World Soil Information and sponsored by the IUSS and the FAO and was designed to cater for any soil in the world.

WRB is a two-tier system of soil classification, with 32 Major Soil Groups (the “Reference Base”) and over 120 uniquely defined qualifiers for specific soil characteristics (the “WRB Classification System”).

The fourth edition (2022) is the currently valid WRB: Download document.

The definitions in the WRB are based on field and laboratory data:

• Field data collection is outlined in the FAO Guidelines for Soil Description (FAO 2006). 
• Laboratory procedures are outlined in the Procedures for Soil Analysis (Van Reeuwijk 2002). This is published by ISRIC–World Soil Information.

This open source article provides an excellent introduction to the WRB classification system.

For more information, visit the website of the IUSS Working Group WRB.