Diagnostic horizons in substantive-genetic soil classification systems

Three classification systems-the new classification of Russian soils, the most recent version of Soil Taxonomy, and the World Reference Base for Soil Resources (WRB)-have been compared with respect to their conceptual backgrounds 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 diagnostic criteria of soil horizons, quantitative boundaries of diagnostic properties, and approaches to classification of human-modified soils. The difference between the new Russian system and the Soil Taxonomy is more pronounced than that between the Russian system and the WRB. A thorough analysis of diagnostic horizons should precede the correlation of soil units and legends of soil maps.