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ARS Home » Plains Area » Lincoln, Nebraska » Agroecosystem Management Research » Research » Publications at this Location » Publication #314307
Title: Sub-surface soil carbon changes affects biofuel greenhouse gas emissions

Author
item Schmer, Marty
item Jin, Virginia
item Wienhold, Brian

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2015
Publication Date: 6/2/2015
Publication URL: http://handle.nal.usda.gov/10113/61151
Citation: Schmer, M.R., Jin, V.L., Wienhold, B.J. 2015. Sub-surface soil carbon changes affects biofuel greenhouse gas emissions. Biomass and Bioenergy. 81:31-34. DOI: 10.1016/j.biombioe.2015.05.011.

Interpretive Summary: Biofuel feedstocks are being developed and evaluated in the United States and Europe to partially offset petroleum transport fuels. Accurate accounting of upstream and downstream greenhouse gas (GHG) emissions is necessary to measure the overall carbon intensity of new biofuel feedstocks. Changes in direct soil organic carbon (SOC) can have a major impact on estimating overall greenhouse gas (GHG) emissions from biofuels. In particular, changes in sub-surface soil depths (>30 cm) could have a large impact on overall GHG emissions from biofuels either positively or negatively that are not always accounted for. We demonstrate how accounting for sub-surface carbon changes from long-term field experiments impact biofuel GHG emissions for corn (Zea mays L.) grain, corn stover, and switchgrass (Panicum virgatum L.) using the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model. Corn grain and cellulosic ethanol GHG emissions varied either positively or negatively from baseline GHG emissions depending on SOC changes at near and sub-surface depths. Differences in GHG emission values highlight the importance of accounting for sub-surface SOC stock changes especially in bioenergy cropping systems with high potential for soil C storage.

Technical Abstract: Changes in direct soil organic carbon (SOC) can have a major impact on overall greenhouse gas (GHG) emissions from biofuels when using life-cycle assessment (LCA). Estimated changes in SOC, when accounted for in an LCA, are typically derived from near-surface soil depths (<30 cm). Changes in subsurface soil depths (>30 cm) could have a large positive or negative impact on overall GHG emissions from biofuels that are not always accounted for. Here, we evaluate how sub-surface SOC changes impact biofuel GHG emissions for corn (Zea mays L.) grain, corn stover, and switchgrass (Panicum virgatum L.) using the (Greenhouse Gases, Regulated Emissions, and Energy Use in the Transportation) GREET model. Biofuel GHG emissions showed as much as a 154% difference between using near-surface SOC stocks changes only or when accounting for both near- and sub-surface SOC stock changes. Differences in GHG emissions highlight the importance of accounting for sub-surface SOC changes especially in bioenergy cropping systems with potential for soil C storage to deeper soil depths.