Diagnostic horizons in substantive-genetic soil classification systems

Three classification systems-the new classification of Russian soils, the m ost recent version of Soil Taxonomy, and the World Reference Base for Soil Resources (WRB)-have been compared with respect to their conceptual backgro unds and criteria used to specify the diagnostic horizons. The distinctions between the Russian and foreign systems are very significant even when the horizons have similar names. This is conditioned by the difference in diag nostic criteria of soil horizons, quantitative boundaries of diagnostic pro perties, and approaches to classification of human-modified soils. The diff erence between the new Russian system and the Soil Taxonomy is more pronoun ced than that between the Russian system and the WRB. A thorough analysis o f diagnostic horizons should precede the correlation of soil units and lege nds of soil maps.