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Associated Title(s): Global Change Biology
Biochar weathering alters soil greenhouse gas production
In this study, Spokas evaluates the impacts of biochar field aging (e.g. weathering) on observed GHG production/consumption. Hardwood, wood pellet, and macadamia nut shell-derived biochars were applied to an agricultural field and incorporated into the soil by tilling. Three years after incorporation into the soil, the weathered biochar was recovered and analysed.
The elemental composition, pH and microscopic images of weathered and unweathered biochar were assessed. The impacts of weather and unweather biochar application on net soil GHG production/consumption were assessed through laboratory incubations. GHGs considered were nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2).
The author found that while fresh biochar additions supressed N2O production following incorporation, weathering of biochar did not affect N2O production. Amending the soil with fresh biochar samples suppressed soil CH4 oxidation (i.e. increased CH4 emissions), while amending the soil with weathered biochar did not affect CH4 emissions. Fresh biochar amendments had no effect on CO2 production, while weathered biochars enhanced CO2 production.
This study demonstrates that for these three biochars, weathering greatly alters the GHG response of the soil systems to biochar amendments. Of particular importance is the increased N2O production of soil amended with weathered biochar. These results cast doubt on the long-term duration of the mitigation of soil N2O emissions by biochar additions.
Spokas KA (2013) Impact of biochar field aging on laboratory greenhouse gas production potentials. GCB Bioenergy, 5, 165–176. doi: 10.1111/gcbb.12005 Read this paper
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