Life-cycle assessment of net greenhouse-gas flux for bioenergy cropping systems.

Bioenergy cropping systems could help offset greenhouse gas emissions, but quantifying that offset is complex. Bioenergy crops offset carbon dioxide emissions by converting atmospheric CO2 to organic C in crop biomass and soil, but they also emit nitrous oxide and vary in their effects on soil oxidation of methane. Growing the crops requires energy (e.g., to operate farm machinery, produce inputs such as fertilizer) and so does converting the harvested product to usable fuels (feedstock conversion efficiency). The objective of this study was to quantify all these factors to determine the net effect of several bioenergy cropping systems on greenhouse-gas (GHG) emissions. We used the DAYCENT biogeochemistry model to assess soil GHG fluxes and biomass yields for corn, soybean, alfalfa, hybrid poplar, reed canarygrass, and switchgrass as bioenergy crops in Pennsylvania, USA. DAYCENT results were combined with estimates of fossil fuels used to provide farm inputs and operate agricultural machinery and fossil-fuel offsets from biomass yields to calculate net GHG fluxes for each cropping system considered. Displaced fossil fuel was the largest GHG sink, followed by soil carbon sequestration. N20 emissions were the largest GHG source. All cropping systems considered provided net GHG sinks, even when soil C was assumed to reach a new steady state and C sequestration in soil was not counted. Hybrid poplar and switchgrass provided the largest net GHG sinks, >200 g CO2e-C x m(-2) x yr(-1) for biomass conversion to ethanol, and >400 g CO2e-C x m(-2) x yr(-1) for biomass gasification for electricity generation. Compared with the life cycle of gasoline and diesel, ethanol and biodiesel from corn rotations reduced GHG emissions by approximately 40%, reed canarygrass by approximately 85%, and switchgrass and hybrid poplar by approximately 115%.

[1]  K. Paustian,et al.  Energy and Environmental Aspects of Using Corn Stover for Fuel Ethanol , 2003 .

[2]  Vemap Participants Vegetation/ecosystem modeling and analysis project: Comparing biogeography and biogeochemistry models in a continental-scale study of terrestrial ecosystem responses to climate change and CO2 doubling , 1995 .

[3]  J. Hatfield,et al.  Review and Interpretation: Nitrogen Management Strategies to Reduce Nitrate Leaching in Tile-Drained Midwestern Soils , 2002 .

[4]  Peter E. Thornton,et al.  Generating surfaces of daily meteorological variables over large regions of complex terrain , 1997 .

[5]  R. Lal World crop residues production and implications of its use as a biofuel. , 2005, Environment international.

[6]  Johan Six,et al.  The potential to mitigate global warming with no‐tillage management is only realized when practised in the long term , 2004 .

[7]  John Sheehan,et al.  Life cycle inventory of biodiesel and petroleum diesel for use in an urban bus. Final report , 1998 .

[8]  R. Lal,et al.  Carbon emission from farm operations. , 2004, Environment international.

[9]  M. Casler,et al.  Low Intensity Harvest Management of Reed Canarygrass , 2003 .

[10]  R. Nelson Resource assessment and removal analysis for corn stover and wheat straw in the Eastern and Midwestern United States—rainfall and wind-induced soil erosion methodology , 2002 .

[11]  S Pacala,et al.  Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies , 2004, Science.

[12]  D. Kruger,et al.  Good practice guidance and uncertainty management in national greenhouse gas inventories , 2000 .

[13]  John R. Williams,et al.  EPIC-erosion/productivity impact calculator: 1. Model documentation. , 1990 .

[14]  I. GWPs,et al.  GREENHOUSE GAS FLUXES IN TROPICAL AND TEMPERATE AGRICULTURE : THE NEED FOR A FULL-COST ACCOUNTING OF GLOBAL WARMING POTENTIALS , 2003 .

[15]  Karen Updegraff,et al.  Environmental benefits of cropland conversion to hybrid poplar: economic and policy considerations , 2004 .

[16]  D. Schimel,et al.  Simulated effects of dryland cropping intensification on soil organic matter and greenhouse gas exchanges using the DAYCENT ecosystem model. , 2002, Environmental pollution.

[17]  Michael Q. Wang,et al.  The Energy Balance of Corn Ethanol: An Update , 2002 .

[18]  Danielle Prévost,et al.  Emissions of N2O from Alfalfa and soybean crops in Eastern Canada , 2004 .

[19]  Carolien Kroeze,et al.  Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories : Chapter 4. Agriculture , 1997 .

[20]  W. Parton,et al.  DAYCENT and its land surface submodel: description and testing , 1998 .

[21]  Akwasi A. Boateng,et al.  Biomass Yield and Biofuel Quality of Switchgrass Harvested in Fall or Spring , 2006 .

[22]  Keith A. Smith,et al.  Impacts of land management on fluxes of trace greenhouse gases , 2004 .

[23]  C. Sheaffer,et al.  Population Density and Harvest Maturity Effects on Leaf and Stem Yield in Alfalfa , 2003 .

[24]  J. Scurlock,et al.  The development and current status of perennial rhizomatous grasses as energy crops in the US and Europe , 2003 .

[25]  K. Paustian,et al.  Carbon Storage in Soils of the North American Great Plains: Effect of Cropping Frequency , 2005 .

[26]  J. Anderson,et al.  Plant litter quality and decomposition: an historical overview , 1997 .

[27]  John Sheehan,et al.  Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus , 1998 .

[28]  Arvin R. Mosier,et al.  DAYCENT model analysis of past and contemporary soil N2O and net greenhouse gas flux for major crops in the USA. , 2005 .

[29]  Stephen P. Slinsky,et al.  Bioenergy Crop Production in the United States: Potential Quantities, Land Use Changes, and Economic Impacts on the Agricultural Sector , 2003 .

[30]  Martin Heller,et al.  Life cycle energy and environmental benefits of generating electricity from willow biomass , 2004 .

[31]  H. W. Hunt,et al.  Management options for reducing CO2 emissions from agricultural soils , 2000 .

[32]  Michael Wang,et al.  Development and use of GREET 1.6 fuel-cycle model for transportation fuels and vehicle technologies. , 2001 .

[33]  Andrew D. Jones,et al.  Supporting Online Material for: Ethanol Can Contribute To Energy and Environmental Goals , 2006 .

[34]  W. Rawls,et al.  Estimating generalized soil-water characteristics from texture , 1986 .

[35]  H. Janzen Carbon cycling in earth systems—a soil science perspective , 2004 .

[36]  Keith A. Smith,et al.  General CH4 oxidation model and comparisons of CH4 Oxidation in natural and managed systems , 2000 .

[37]  Gary A. Peterson,et al.  Chapter 16 – Simulated effects of land use, soil texture, and precipitation on N gas emissions using DAYCENT , 2001 .

[38]  Tristan R. Brown,et al.  Biorenewable Resources: Engineering New Products from Agriculture , 2003 .

[39]  H. Echeverría,et al.  Crop rotations and nitrogen fertilization to manage soil organic carbon dynamics. , 2000 .

[40]  Raffaele Spinelli,et al.  Delimbing hybrid poplar prior to processing with a flail/chipper , 2000 .

[41]  Gregg Marland,et al.  CO2 emissions from the production and combustion of fuel ethanol from corn , 1991 .

[42]  Allen C. McBride,et al.  The contribution of agricultural lime to carbon dioxide emissions in the United States: dissolution, transport, and net emissions , 2005 .

[43]  W. Parton,et al.  Simulated Interaction of Carbon Dynamics and Nitrogen Trace Gas Fluxes Using the DAYCENT Model1 , 2006 .

[44]  D. Laird,et al.  Impact of Nitrogen Fertilization and Cropping System on Carbon Sequestration in Midwestern Mollisols , 2005 .

[45]  David E. Kissel,et al.  Crop rotation and tillage effects on soil organic carbon and nitrogen , 1990 .

[46]  G. Keoleian,et al.  Life cycle assessment of a willow bioenergy cropping system , 2003 .

[47]  K. Paustian,et al.  Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils , 2002, Plant and Soil.

[48]  W. Parton,et al.  A general model for soil organic matter dynamics: sensitivity to litter chemistry, texture and management. , 1994 .

[49]  G. Marland,et al.  A synthesis of carbon sequestration, carbon emissions, and net carbon flux in agriculture: comparing tillage practices in the United States , 2002 .

[50]  G. Robertson,et al.  Greenhouse gases in intensive agriculture: contributions of individual gases to the radiative forcing of the atmosphere , 2000, Science.

[51]  Peter E. Thornton,et al.  Simultaneous estimation of daily solar radiation and humidity from observed temperature and precipitation: an application over complex terrain in Austria. , 2000 .

[52]  Jeffrey S. Dukes,et al.  Burning Buried Sunshine: Human Consumption of Ancient Solar Energy , 2003 .

[53]  Robert B. Mitchell,et al.  Chemical composition and response to dilute-acid pretreatment and enzymatic saccharification of alfalfa, reed canarygrass, and switchgrass , 2006 .

[54]  B. Dale,et al.  Cumulative Energy and Global Warming Impact from the Production of Biomass for Biobased Products , 2003 .

[55]  V. R. Tolbert,et al.  High-value renewable energy from prairie grasses. , 2002, Environmental science & technology.

[56]  Seungdo Kim,et al.  Environmental aspects of ethanol derived from no-tilled corn grain: nonrenewable energy consumption and greenhouse gas emissions , 2005 .

[57]  L. L. Oden,et al.  The behavior of inorganic material in biomass-fired power boilers: Field and laboratory experiences , 1998 .

[58]  S. Running,et al.  An improved algorithm for estimating incident daily solar radiation from measurements of temperature, humidity, and precipitation , 1999 .

[59]  M. Mann,et al.  Biomass Power and Conventional Fossil Systems with and without CO2 Sequestration – Comparing the Energy Balance, Greenhouse Gas Emissions and Economics , 2004 .

[60]  Vincent Mahieu,et al.  Well-to-wheels analysis of future automotive fuels and powertrains in the european context , 2004 .

[61]  C. Alan Rotz The Integrated Farm System Model: A Tool for Developing more Economically and Environmentally Sustainable Farming Systems for the Northeast , 2004 .

[62]  B. McCarl,et al.  Greenhouse Gas Mitigation in U.S. Agriculture and Forestry , 2001, Science.

[63]  Liwang Ma,et al.  Modeling Carbon and Nitrogen Dynamics for Soil Management , 2001 .

[64]  B. Dale,et al.  Global potential bioethanol production from wasted crops and crop residues , 2004 .

[65]  W. Post,et al.  Soil organic carbon sequestration rates by tillage and crop rotation : A global data analysis , 2002 .

[66]  R. Lal,et al.  Crop Management for Soil Carbon Sequestration , 2003 .