Podzolization over ophiolitic materials in the western Alps (Natural Park of Mont Avic, Aosta Valley, Italy)

Soil surveys carried out on ophiolitic rocks and till under subalpine forest in the Natural Park of Mont Avic (Aosta Valley, West Italian Alps) revealed the unexpected occurrence of soils showing a horizon set typical of the podzols. Podzolization is uncommon on mafic and ultramafic substrata: the translocation of organo-metallic compounds in soils developed from such parent materials slows down considerably due to the high Fe and Mg contents, the high base saturation and the close to neutral pH. In order to determine the real origin and evolution of such soils, 6 pedons, selected among 83 profiles with a similar “podzol” morphology, were sampled and analyzed. Chemical, mineralogical, and petrographic analyses of the sampled soils and parent materials were performed, and correlation analysis of the obtained data was carried out. Results show that, in favourable environmental conditions (mainly climate and vegetation), even mafic and ultramafic parent materials can undergo different degrees of podzolization. Due to the adopted diagnostic criteria the most common classification systems (particularly the WRB) do not allow satisfactory taxonomic arrangement of such soils.