Tailoring biochar properties via co-pyrolysis for enhanced C stabilization and organo-mineral interactions

The sustainable management of agro-industrial residues through biochar production has emerged as a key strategy for enhancing soil organic matter (SOM) functionality and long-term carbon sequestration. However, the capacity of biochar to stabilize carbon and interact with SOM pools is governed by its physicochemical properties, which are defined by feedstock and thermal processing. This study evaluated biochars produced by pyrolysis and co-pyrolysis to assess their potential roles in C stabilization and SOM-mediated processes. Biochars were derived from poultry litter, coconut fibre, rotary sieve residue, and charcoal fines, processed individually and in co-pyrolysed blends at 500 °C. Characterisation included yield, pH, CEC, BET surface area, elemental composition (CHN), and structural/morphological analyses (XRD, FTIR, SEM). The results revealed that feedstock composition dictates the aromaticity and recalcitrance of the resulting pyrogenic carbon. Coconut fibre biochar exhibited exceptionally high fixed carbon content (70.83%) and elevated surface area, indicating strong potential to promote physical protection of SOM and increase the soil's recalcitrant C pool. In contrast, poultry litter-based biochars and their co-pyrolysed derivatives provided high mineral content and alkalinity, which can influence the organo-mineral interactions and the turnover of native SOM. Co-pyrolysis proved to be an effective strategy to optimize the functional groups and structural porosity of the materials. Multivariate analysis confirmed that co-pyrolysis can be used to "engineer" biochars that balance water retention with carbon persistence. Overall, this study demonstrates that tailoring biochar properties through co-pyrolysis is a viable pathway for improving C storage and reinforcing the role of SOM in sustainable ecosystem services