Comparison between Ancient and Fresh Biochar Samples, A Study on The Recalcitrance of Carbonaceous Structures During Soil Incubation

Biochar (BC) is a carbonaceous product that comes from pyrolysis process of different biomasses, such as lignocellulosic feedstocks. Biomass nature, pyrolysis temperature and speed heating rate affect the physical and chemical characteristics of BC produced. The aim of this work concerned the investigation of recalcitrant aspects of carbonaceous structures in biochar's matrix, which evolved during its long time permanence in soil. Using X-Ray diffraction and Raman Spectroscopy, this study was focalized on the evolution of carbonaceous structures with increasing pyrolysis temperature. Fresh samples, produced in laboratory from larch wood feedstock, were compared with ancient fragments (dated 1859), collected in Oriental Alps soils (PejoValley, Trentino, Italy) and produced in ancient kilns from larch wood as well. From this comparison, we found a significant degradation of aliphatic compounds and low-extended aromatic ring systems as a function of incubation time in soil. It was observed, over degradation on carbonaceous structures, signs coming from the interactions with the environment against the time, such as the adsorption processes of mineral elements and encapsulation of mineral crystalline phases, that increase the stability of the carbonaceous residual fractions of biochar. Index Terms— Biochar, carbon, recalcitrance, X-Ray Diffraction, Raman spectroscopy