The World Reference Base for Soil Resources

Abstract

The World Reference Base for Soil Resources (WRB) is the successor to the International Reference Base for Soil Classification (IRB). Its task is to apply the IRB principles of definitions and linkages to the existing classes of the Revised FAO-Unesco Soil Map of the World Legend (FAO, 1988). The main objective is to provide scientific depth and background to the Revised Legend, and to ensure that the latest knowledge relating to global soil resources and interrelationships is incorporated in a world-wide soil reference system.

At present, the WRB comprises 30 reference soil groups. Three new reference soil groups, i.e. Cryosols, Durisols and Umbrisols, are introduced compared with the Revised Legend, Greyzems are amalgamated with the Phaeozems, and Podzoluvisols renamed Albeluvisols. The concept and terminology of diagnostic horizons and properties is retained and expanded. In addition, diagnostic soil materials are defined. In the description and definition of the WRB diagnostic horizons, properties and materials emphasis is placed on field identification. Analytical criteria are given to help the identification. Some modifications are proposed to diagnostic horizons, properties and materials as defined in the Revised Legend and a number of new ones are formulated.

The basic philosophy of WRB is that the soil groups must represent a minimal geographical coverage and are the result of a major pedogenetic process. Soils are characterized by their morphological expression rather than by analytical data.

Ferralsols, Acrisols, Lixisols, Alisols and Nitisols constitute the main reference soil groups in tropical forest ecosystems occupying well drained upland positions. Other soil groups of local or regional importance are Andosols, Podzols, Umbrisols and Arenosols. The main soils occupying poorly drained positions in the tropics are Histosols, Fluvisols, Plinthosols, Gleysols and, to a lesser extent, Planosols. On one hand, the World Reference Base for Soil Resources, like the FAO-Unesco Legend, continues to build up on existing soil classification systems. Examples are the description, definition and subdivision of Anthrosols and Andosols. On the other hand, some proposals result from new ideas which are not yet reflected in published classification systems.

The final aim is a well described and defined World Reference Base for Soil Resources that is internationally accepted by the community of soil scientists. It also intends to facilitate the international use of pedological data, not only by soil scientists, but also by other users of soil and land.