The WRB (World Reference Base for Soil Resources)--An Overview.

WRB is an international soil classification system. The current version is Update One (2007) of the Second Edition (2006). WRB has little hierarchy with only two categoric levels. The upper level comprises 32 Reference Soil Groups (RSGs) identified by a key. The names of the lower level are constructed by adding adjectives, the qualifiers, to the names of the RSGs. We have 179 qualifiers, many of them mutually exclusive, defined in a common alphabetical list. For every RSG an individual list defines which ones of these 179 qualifiers are allowed, resulting in lists from 21 to 57 qualifiers. For correct classification of an individual soil at the second level, all applicable qualifiers must be recorded. In reality, individual soils having between one and ten qualifiers have been reported. Whereas the RSGs are defined along the broad lines of soil forming factors and processes, the qualifiers carry a lot of information for practical purposes. Qualifiers inform about base status, texture, coarse material, burying material, mineralogy, soil depth, organic matter content, accumulating substances and many other chemical and physical characteristics. They also reflect intergrades with other RSGs. The definitions of both, RSGs and qualifiers, are based on diagnostic horizons, properties, and materials.

With the qualifier system, WRB is flexible (a soil has just as much as qualifiers as it needs) and relatively exhaustive (provides the soil properties important for many applications). Using WRB for mapping creates some problems because maps, even on the largest scale, cannot provide such large amounts of qualifiers. And the qualifiers, although divided into prefix and suffix ones, do not show a hierarchical ranking. Therefore, the mapper, according to his purposes, has to select the qualifiers which should be shown on the map.

The presentation will give examples for both, classification and mapping with different handlings of qualifiers.