The beneficial use of basalt flour combined to a microbial consortium to improve soil quality in basalt and carbonatic dismissed quarries

The recovery of degraded soils to restore their capacity to carry out important ecological functions such as promoting nutrient cycling is a very topical issue. The aim of the present work was to assess soil quality changes within two different disused quarries in central Italy (named Cornale and Poggio Tabor) through the addition of basalt flour combined with a microbial consortium (BBF) (2.7 kg of basalt flour and 54 ml of microbial consortium inoculum at each supply date). Soil samples were collected within 9 plots where three treatments 1) Control (C) no treatment; 2) bioactive basalt flour (BBF) and 3) bioactive basalt flour and cover crop (BBF + CC) were randomly replicated three times per quarry. Chemical indicators showed little changes due to the different amendments, conversely, the biochemical ones showed that the addition of BBF increased enzymatic activities involved in C, N, P, and S cycling, and promoted microbial growth and C mineralization activity at both studied sites. At the Cornale site in summer, the rooting of the cover crop, through the rhizodeposition provided the carbon substrates necessary to fuel the added microorganisms showing an increase in the microbial quotient of about 5 % compared to the control soil. Conversely, at the Poggio Tabor site, the peculiar geomorphology prevented the cover crop growth; therefore, the positive responses of enzymatic activities were evident only in the BBF treated plots. From a management perspective, the use of bioactive basalt flour consisting of basalt flour and microbial consortium could be a good strategy to restore soil quality according to nutrient cycling function in a degraded area. However, in highly limited organic matter conditions, an external input of organic carbon is strongly recommended to sustain the exogenous microbial consortium.