Classification of the reference pedons: World reference base for soil resources and soil taxonomy

Abstract

The soil classification systems used are the World Reference Base (WRB) for Soil Resources (Driessen et al. 2001) and the USDA Keys to Soil Taxonomy (Soil Survey Staff 2003); in addition the French pedons EUR16 & 17 have also been classified according to the Référentiel Pédologique Français (AFES 1995). WRB is currently under revision, including the Andosols. In the discussion attention will be given to the proposed revisions in WRB (FAO-ISRIC-IUSS, in preparation), in particular to the new diagnostic criteria for the andic, vitric, and fulvic horizons, which provide better correlation with Soil Taxonomy. The Reference Pedons of European Volcanic Soils are mostly Andosols (WRB, RPF) or Andisols (ST). However, in Greece Regosols (WRB) or Entisols (ST) occur, whereas in Hungary Phaeozems and Umbrisols (WRB) or Haploxerolls and Haploxerepts (ST) are found. The Andosol classification for the French 'Référentiel Pédologique' and the World Reference Base for Soil Resources are fairly well correlated, at least at the higher levels. The WRB draft, after a first presentation to the 15th World Congress of Soil Science (Quantin 1994), and some remarks by Shoji et al. (1996), some adjustments were made by Berding (1997) for the first edition (FAO-ISRIC-ISSS 1998); then it was revised (Driessen et al. 2001). But after remarks of some COST Action 622 contributors and recent 'proposed revisions' of Takahashi et al. (2004), the definitions of diagnostic horizons Andic/Vitric and Fulvic/Melanic are currently under revision (FAO-ISRIC-IUSS in preparation), in view of a better correlation with the Soil Taxonomy. The definition of Andosols (AFES 1995, Driessen et al. 2001) or Andisols (Soil Survey Staff 2003) is essentially based upon 'andic soil properties', briefly:-for the Andic horizon: Alo + 1/2Feo at least 2%, P-retention at least 70% (in <2 mm fraction), and bulk density at most 0.9 g dm-3;-for the Vitric horizon: Alo + 1/2Feo of 0.4-2% and a P-retention of at least 25%. In addition, WRB requires for a Vitric horizon a volcanic glass content of at least 10%, whereas the Andic horizon should have less than 10% volcanic glass, as well as 10% or more clay. Contrary to Soil Taxonomy, WRB and RPF do not use soil moisture and soil temperature regimes, such as aquic, cryic, udic, ustic, xeric, etc., as dividing criteria at the suborder level. WRB recognises only two levels: the Major Reference Group (MRG) level and the qualifier level (FAO-ISRICIUSS 1998, Nachtergaele et al. 2002). Each MRG has its own ranked listing of qualifiers. In Andosols the list of qualifiers is headed by Vitric, Silandic and Aluandic, which correlate in RPF with Vitrisol, Silandosol and Aluandosol. Then follow characteristics typical of Andosols, viz. Eutrisilic, Melanic, Fulvic and Hydric. The list is completed by qualifiers as Histic, Mollic, Umbric, Placic, Pachic, etc. If buried diagnostic horizons occur, like Melanic or Mollic, the modifier Thapto may be used, e.g. Thaptomelanic or Thaptomollic. WRB also offers the opportunity to use modifiers to indicate the position of certain horizons in the soil, e.g. Epi-for an occurrence within 50 cm from the soil surface, and Endo-for a presence between 50 and 100 cm depth, or to indicate weak or strong development (Hypo-or Hyper-). © Springer-Verlag Berlin Heidelberg 2007.