Comparison of natural and technogenic soils developed on volcanic ash by Vis-NIR spectroscopy

Soil biological properties and carbon storage of three young Technosols deriving from volcanic soil of Campi Flegrei, Italy, were compared with two natural volcanic soils, sampled from two forest ecosystem sites (chestnut and Mediterranean maquis). The soil properties were examined with Vis-NIR spectroscopy and portable XRF, along the soil profile. The results showed that the average soil organic matter (SOM) amount in Technosols profiles were lower than in natural volcanic soils. The differences in SOM content between the two investigated natural volcanic soils probably resulted from their land-use histories and different plant cover. Indeed, the chestnut soil profile, which has a higher SOM content, was covered by an old chestnut grove, while the second soil profile, after a severe burning, showed a change in natural Oak forest vegetation towards the typical Mediterranean maquis. The microbial biomass can be predicted with Vis-NIR spectroscopy coupled with PLS Regression. Our results showed that 6-year natural incorporation of organic residue in Technosols significantly increased the C storage on the top soils due to the increase in C input with rhizodeposition. The forest soils show higher TOC content also with the depth that indicate a greater capacity of C storage in response to litter incorporation, whereas the Technosols accumulated about half the amount of TOC, compared to the chestnut grove. Indeed, after six years of natural vegetation, the Technosols showed a large potential to sequester C and to sustain biological activity. Overall, the emerging knowledge on technosols make them highly promising for the regeneration of urban area.