Interpretation of pre-AD 472 Roman soils from physicochemical and mineralogical properties of buried tephric paleosols at Somma Vesuviana ruin, southwest Italy

This study aimed to interpret soil fertility around Somma Vesuviana in ancient Rome from investigation of buried paleosols developed beneath thick pumice deposits of the AD 472 Pollena eruption of Mt. Vesuvius. Two buried pedons derived mainly from phonolitic tephra deposits of the AD 79 Pompeii eruption, and ancient construction waste, were excavated and sampled at the Somma Vesuviana villa ruins on the northern flanks of Mt. Vesuvius, Italy. For comparison, a buried paleosol on equivalent Pompeii tephra deposits in a nearby forest, and a modern soil on AD 1631 tephra deposits (compositionally similar to Pompeii eruptives) in an adjacent orchard, were similarly analyzed for physical, chemical, and mineralogical properties, including phosphorus fractions and primary mineral compositions. The two buried pedons in the ruin had abundant available P and K and contained moderate amounts of exchangeable cations. Leucite was the dominant primary mineral and, with alkali feldspars, is probably the major source of K in the buried horizons. A high content of “authigenic P (Ca-bound P)” characterized all the pedons. We concluded that the buried Somma Vesuviana paleosols had a relatively high ability to supply nutrients and that they were fertile prior to the AD 472 eruption, although manuring to increase nitrogen was probably needed to maintain high productivity. Their physical properties such as water retention were probably enhanced by small but significant amounts of short-range order clays.