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Impact of biochar field aging on laboratory greenhouse gas production potentials

Spokas, Kurt A.
Global change biology 2013 v.5 no.2 pp. 165
biochar, carbon dioxide, gas production (biological), greenhouse gas emissions, greenhouse gases, hulls, macadamia nuts, methane, methanotrophs, mineralization, nitrous oxide, oxidation, soil, soil amendments, soil microorganisms, weathering, wood
Recent observations of decreased greenhouse gas (GHG) production from biochar amended soils have been used to further substantiate the environmental benefit of biochar production and soil incorporation strategies. However, the mechanisms behind this biochar-mediated response have not been fully elucidated. In addition, the duration of these GHG reductions is not known and is of pivotal importance for the inclusion of biochar into future bioenergy production and climate abatement strategies. In this study, the impacts of biochar field aging on the observed GHG production/consumption were evaluated. Two different wood-derived biochars and a macadamia nut shell biochar were weathered in an agricultural field in Rosemount, MN (2008-2011) and the impacts on net soil GHG production/consumption were assessed through laboratory incubations. For the three biochars evaluated here, weathering negated the suppression of N2O production that was originally observed from the fresh biochar in laboratory incubations. On the other hand, all three weathered biochars had enhanced CO2 production (three- to ten fold compared to the fresh biochar amendments) in laboratory soil incubations, suggesting an enhanced microbial mineralization rate for the weathered biochar. Fresh biochar reduced observed soil methane oxidation rates, while the weathered biochars had no significant impacts on the observed soil methanotrophic activity. This study demonstrates that for these three biochars weathering greatly alters the GHG response of the soil systems to biochar amendments.