A proposal for including humus forms in the World Reference Base for Soil Resources (WRB-FAO)

The morpho-functional classification of humus forms proposed in a previous issue by Zanella and collaborators for Europe has been extended and modified, without any change in diagnostic horizons, in order to embrace a wide array of humus forms at worldwide level and to complete and make more effective the World Reference Base for Soil Resources. For that purpose 31 Humus Form Reference Groups (HFRGs) and a set of prefix and suffix qualifiers are proposed, following the rules erected for the WRB. An exhaustive classification key, respecting the principles of WRB, is suggested and examples of classification are given for some already well known humus forms. ► A World Reference Base for Humus Forms is now available following the rules erected for the WRB. ► A wide array of terrestrial and semi-terrestrial humus forms at worldwide level are considered. ► 31 Humus Form Reference Groups and a set of prefix and suffix qualifiers are proposed. ► An exhaustive classification key is suggested. ► Examples of classification are given for well-known humus forms.