ARS | Publication request: Impact of field exposure on greenhouse gas production potentials from biochar additions

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2011
Publication Date: October 16, 2011
Citation: Spokas, K.A. 2011. Impact of field exposure on greenhouse gas production potentials from biochar additions. ASA-CSSA-SSSA Annual Meeting Abstracts. Abstract #205-7.

Technical Abstract: A potential abatement strategy to increasing atmospheric levels of carbon dioxide (CO2) is to sequester atmospheric CO2 into a more stable form through the pyrolysis of biomass. Biomass feed stocks are used to generate a more stable carbon form (biochar) that when added to soils can act place atmospheric C into a slowly cycling pool as well as potential alterations in plant growth/yield and microbial soil processes. However, the mechanisms behind the “biochar effect” have not been fully elucidated. In the present work, we have examined the impact of field aging of two different hardwood biochars on the net greenhouse gas (GHG) production through laboratory soil incubations. There were no unified trends observed in the effect of field aging on these two biochars. The first biochar was a fast-pyrolysis hardwood biochar (500 oC). For this fast pyrolysis biochar, both aged and fresh biochar amendments reduced N2O production compared to unamended soil. The field aging of this biochar resulted in lower N-mineralization rates, primarily from a reduction in the extractable nitrate (60-70% reduction compared to the fresh biochar). On the other hand, the slow pyrolysis hardwood biochar (550 oC), observed no significant impact in the N2O production or nitrate/ammonium availability in the initial soil incubations of the fresh biochar. CO2 production in the fresh biochar amended soil was suppressed. Upon field aging, this slow pyrolysis biochar stimulated both N2O and CO2 production compared to the original unamended soil as well as the fresh biochar amended soil. Furthermore, the field-aged slow pyrolysis biochar had higher extractable N forms than the fresh biochar. Both biochars showed remarkable reductions in the presence of sorbed organic compounds due to field aging. These contrasting results in the GHG production indicate that the impact on the soil microbial GHG production is a balance of multiple factors. One of these is the role of the surface oxygen groups, since the oxygen content of both biochar materials did increase to differing degrees following environmental exposure. These surface oxygen groups can control the interaction of the biochar with the environment, which historically has been observed for black carbons.