One potential abatement strategy to increasing atmospheric levels of carbon dioxide (CO2) is to sequester atmospheric CO2 captured through photosynthesis in biomass and pyrolysed into a more stable form of carbon called biochar. We evaluated the impacts of 16 different biochars from different pyrolysis/gasification processes and feed stock materials (corn stover, peanut hulls, macadamia nut shells, wood chips, and turkey manure plus wood chips) as well as a steam activated coconut shell charcoal on net CO2, methane (CH4) and nitrous oxide (N2O) production/consumption potentials through a 100 day laboratory incubation with a Minnesota agricultural soil (Waukegan silt loam, total organic carbon = 2.6%); Wisconsin forest nursery soil (Vilas loamy sand, total organic carbon = 1.1%); and a California landfill cover soil (Marina loamy sand plus green waste-sewage sludge, total organic carbon = 3.9%) at field capacity (soil moisture potential = -33 kPa). After correcting for the CO2, CH4 and N2O production of the char alone, the addition of biochars (10% w/w) resulted in different responses among the soils. For the agricultural soil, five chars increased, three chars reduced and eight had no significant impact on the observed CO2 respiration. In the forest nursery soil, three chars stimulated CO2 respiration, while the remainder of the chars suppressed CO2 respiration. In the landfill cover soil, only two chars increased observed CO2 respiration, with the remainder exhibiting lower CO2 respiration rates. All chars and soil combinations resulted in decreased or unaltered rates of CH4 oxidation, with no increases observed in CH4 oxidation or production activity. Biochar additions generally suppressed observed N2O production, with the exception being high nitrogen compost-amended biochar, which increased N2O production. The general conclusions are: (1) the impact on trace gas production is both dependent on the biochar and soil properties and (2) biochar amendments initially reduce microbial activity in laboratory incubations. These preliminary results show a wide diversity in biochar properties that point to the need for more research.
