Physical Disintegration of Biochar: An Overlooked Process

Data collected from both artificially and field (naturally) weathered biochar suggest that a potentially significant pathway of biochar disappearance is through physical breakdown of the biochar structure. Via scanning electron microscopy, we characterized this physical weathering that increased the number of structural fractures and yielded higher numbers of liberated biochar fragments. This was hypothesized to be due to the graphitic sheet expansion accompanying water sorption coupled with comminution. These fragments can be on the microscale and the nanoscale but are still carbon-rich particles with no detectable alteration in the oxygen:carbon ratio from that of the original biochar. However, these particles are now easily dissolved and could be moved by infiltration. There is a need to understand how to produce biochars that are resistant to physical degradation to maximize long-term biochar C sequestration potential within soil systems.