Changes in chemical and physical characteristics of biochar after long-aging in soil by LIBS technique

Biochar (BC) is the focus of several studies, both in agronomic and climate domain. BC is considered a great strategy for the mitigation of climate change. It is obtained by pyrolysis and pyrogasification of biomass. This material contains substantial amounts (60-90%) of pyrogenic carbon, which is a recalcitrant material that is hardly decomposed by means of biotic and abiotic oxidation. The mitigation potential of biochar is due to the fact that carbon is not easily returned into the atmosphere, even after very long times of incubation in the soil. Few studies have quantified the theoretical carbon sequestration potential of BC after its incubation into agricultural soil and the understanding of the mechanisms and the consequences of the long-term decomposition process of in soil needs to be improved. Indeed, few of the materials considered have been produced in the past and on that base the mean residence time of biochar have been estimated to be of the order of centennial time scale. We have studied C decomposition in soil and reliably calculated the fraction of C that was lost over 155 years for an old BC. Part of our study has been focused on the elemental composition inside the old BC in comparison with the modern one. This aspect has been looked after using LIBS technique that is an innovative approach in the 'bio-climatic' domain. The data concerning the analysis of chemical elements present in the fragments of ancient and modern biochar have been collected. In particular, we quantified the individual presence of hydrogen, oxygen and carbon, so far detected 'together' using standard Loss on Ignition (LOI) methodology.