Abiotic and Microbial Oxidation of Laboratory-Produced Black Carbon (Biochar)

Pyrogenic or "black" carbon is a soil and sediment component that may control pollutant migration. Biochar, black carbon made intentionally by biomass pyrolysis, is increasingly discussed as a possible soil amendment to increase fertility and sequester carbon. Though thought to be extremely refractory, it must degrade at some rate. Better understanding of the rates and factors controlling its remineralization in the environment is needed. Release of CO2 was measured over 1 year from microbial and sterile incubations of biochars made from a range of biomass types and combustion conditions. Carbon release from abiotic incubations was 50-90% that of microbially inoculated incubations, and both generally decreased with increasing charring temperature. All biochars displayed log-linearly decreasing mineralization rates that, when modeled, were used to calculate 100 year C losses of 3-26% and biochar C half-lives on orders ranging from 102 to 101 years. Because biochar lability was found to be strongly controlled by the relative amount of a more aliphatic and volatile component measurements of volatile weight content may be a convenient predictor of biochar C longevity. These results are of practical value to those considering biochar as a tool for soil remediation, amelioration, or atmospheric C sequestration.