Publication Date:
2016-01-05
Description:
Converting land to biofuel feedstock production incurs changes in soil organic carbon (SOC) that can influence biofuel life-cycle greenhouse gas (GHG) emissions. Estimates of these land use change (LUC) and life-cycle GHG emissions affect biofuels’ attractiveness and eligibility under a number of renewable fuel policies in the U.S. and abroad. Modeling was used to refine the spatial resolution and depth-extent of domestic estimates of SOC change for land (cropland, cropland pasture, grasslands, and forests) conversion scenarios to biofuel crops (corn, corn stover, switchgrass, Miscanthus , poplar, and willow) at the county level in the U.S. Results show that in most regions, conversions from cropland and cropland pasture to biofuel crops led to neutral or small levels of SOC sequestration, while conversion of grassland and forest generally caused net SOC loss. SOC change results were incorporated into the Greenhouse Gases, Regulated Emissions, and Energy use in Transportation (GREET) model to assess their influence on life-cycle GHG emissions of corn and cellulosic ethanol. Total LUC GHG emissions (g CO 2 eq MJ −1 ) were 2.1–9.3 for corn-, -0.7 for corn stover-, -3.4–12.9 for switchgrass-, and -20.1–-6.2 for Miscanthus ethanol; these varied with SOC modeling assumptions applied. Extending the soil depth from 30 to 100cm affected spatially-explicit SOC change and overall LUC GHG emissions; however the influence on LUC GHG emissions estimates were less significant in corn and corn stover than cellulosic feedstocks. Total life-cycle GHG emissions (g CO 2 eq MJ −1 , 100cm) were estimated to be 59–66 for corn ethanol, 14 for stover ethanol, 18-26 for switchgrass ethanol, and -7–-0.6 for Miscanthus ethanol. The LUC GHG emissions associated with poplar- and willow-derived ethanol may be higher than that for switchgrass ethanol due to lower biomass yield. This article is protected by copyright. All rights reserved.
Print ISSN:
1757-1693
Electronic ISSN:
1757-1707
Topics:
Energy, Environment Protection, Nuclear Power Engineering
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