The World Reference Base (WRB) for Soil Resources

Reference Base for Soil Resources (WRB) as the Union's system for soil correlation. The structure, concepts and definitions of the WRB are strongly influenced by (the philosophy behind and experience gained with) the FAO-Unesco Soil Classification System. At the time of its inception, the WRB proposed 30 `Soil Reference Groups' accommodating more than 200 (`second level') Soil Units. In the present text (Dreissen et al., 2001), the 30 Reference Soil Groups are aggregated in 10 `sets ' composed as follows: First, a separation is made between organic soils and mineral soils; all organic soils are grouped in Set #1. The remaining (mineral) Major Soil Groups are each allocated to one of nine sets on the basis of `dominant identifiers', i.e. those soil forming factor(s) which most clearly conditioned soil formation. Table 1 summarises the 10 sets, their dominant identifiers and the Reference Soil Groups within each set. SET #1 holds all soils with more than a defined quantity of `organic soil materials'