Biochar promotes the reduction of N₂O to N₂ and concurrently suppresses the production of N₂O in calcareous soil

Biochar additions may mitigate N2O emissions from soil. The mechanisms underpinning the mitigation of emissions remain to be elucidated. A series of incubation experiments were performed to investigate the effects of biochar on N2O production and reduction in columns with a low-fertility or high-fertility soil, with or without the injection of N2O in the subsoil and with and without glucose (to stimulate denitrification). Biochar was added to the calcareous soils in 0 and 1% (w/w) amounts and moisture was maintained at 70% water-filled pore space (WFPS) over the incubation period. The results revealed that biochar reduced the emissions of soil-produced N2O by 37–47% and those of injected N2O by 23–44%. The addition of glucose solution strongly increased N2O emissions, while biochar reduced total N2O emissions by as much as 64–81% and those of injected N2O alone by 29–51%. Differences between the low-fertility and high-fertility soils in the apparent N2O emission mitigation by biochar were relatively small, but tended to be larger for the low-fertility soil. The results suggest that biochar addition can suppress the production of N2O in soil and simultaneously stimulate the reduction of N2O to N2. Further studies are needed to elucidate the regulatory effects of biochar in soil.