Traditional and pedometric approaches to justify the introduction of swelling clay soils as a new soil type in the modernized Hungarian Soil Classification System

Clay and clay loam textured soils that are mainly characterized by smectite dominated mineralogy cover about 25% of the territory of Hungary (Stefanovits and Dombَvلri, 1985). Despite their distinctive morphology, special characteristics and widespread coverage, these soils belong to several different taxonomic units in the current genetic based Hungarian Soil Classification System (HSCS), making the differentiation and definition of several units and correlation with international standards difficult. t of the ongoing modernization process of the HSCS, detailed documentation of high smectite clay content, shrinking and swelling soils developed on different substrates, topographical positions and geographical areas was carried out in Hungary. The collected data was correlated with the World Reference Base for Soil Resources and the dominant soil forming processes were linked to diagnostic elements. The traditional soil classification methodology was supplemented with the modern pedometric method of centroid based taxonomic distance calculation to evaluate the taxonomic relationship between the Hungarian clay soils and the WRB Reference Soil Groups. ndings confirmed that the swelling clay soils of Hungary satisfy the morphological and measureable physical and chemical criteria of the WRB Vertisol Reference Soil Group. The centroid based taxonomic distance calculations were successfully applied for objective expression of similarities and differences between the examined soil types. The studied profiles and the applied methods justify the introduction of swelling clay soils to the highest level of the modernized Hungarian Classification System. The applied methodology can be a useful tool in evaluation, improvement or development of other soil classification systems.