GHG impacts of biochar: Predictability for the same biochar

One potential strategy to abate increasing atmospheric carbon dioxide (CO2) levels is to sequester CO2 as biochar, a structural form of carbon created through the pyrolysis of various biomass materials. Biochar may be applied to soils, but has resulted in variable impacts on net soil greenhouse gas (GHG) emissions, with results spanning from suppression to stimulation. This laboratory incubation study examined the impacts of the same hardwood biochar (fast pyrolysis at 550 °C) to elucidate driving variables affecting previously observed carbon dioxide (CO2) fluctuations as well as nitrous oxide (N2O), and methane (CH4) production impacts across ten different US soils with and without biochar (10% w/w). Biochar application significantly impacted CO2 (P = 0.04) and N2O (P = 0.03) production following amendment across all soils, but there were no differences observed in CH4 production/oxidation rates (P = 0.90). Interestingly, the induced biochar GHG alterations were significantly correlated to the original GHG production activity in the control soil, suggesting a more universal response across various soils to the same biochar than has been previously hypothesized. After correcting for the amount of CO2 released from the biochar itself [24 μg C gBC−1 d−1], there was no statistically significant alteration in the actual soil CO2 mineralization rate for any soil. This suggests that the observed increase in CO2 production was solely attributed to the abiotic CO2 releases from the biochar. On the other hand, there was an average suppression of 63% in the N2O production across all soils following biochar addition, which was again correlated to initial N2O production activity. For this particular biochar, there are predictable impacts on the GHG production potential across various soils despite differences in soil chemistry, texture, and microbial communities.