April 12, 2007

Hybrid poplars reduce carbon emissions best

Renewable Energy Access (REA) reported on a National Renewable Energy Laboratory (NREL) study published in the April 2007 issue of Ecological Applications. It should put to rest any lingering doubts about the advantageous carbon emissions benefits of cellulosic ethanol production - particularly when hybrid poplar feedstock is used.

There is also mention by one of the scientists that "Greenhouse gas savings from biomass gasification for electricity generation are even greater."

Here are some excerpts from the REA story...

Biofuels, Fossil Fuels & the Greenhouse Gas Factor

Researchers at Colorado State University and the U.S. Department of Agriculture, Agricultural Research Service have completed an analysis of greenhouse gas emissions from biofuel production. Study results revealed that when compared with the life cycle of gasoline and diesel, ethanol and biodiesel from corn and soybean rotations reduced greenhouse gas emission by nearly 40 percent, reed canarygrass by 85 percent, and switchgrass and hybrid poplar by 115 percent.

Hybrid poplar and switchgrass were found to offset the largest amounts of fossil fuels and therefore reduced emissions the most out of the studied crops.

"Although fossil fuel inputs are required to produce and process biofuels, hybrid poplar and switchgrass converted to ethanol compensate for these emissions and actually remove greenhouse gasses from the atmosphere when the benefits of co-products are included. Greenhouse gas savings from biomass gasification for electricity generation are even greater."
-- Stephen Del Grosso, USDA scientist and NREL researcher

Ethanol and biodiesel from corn and soybean are currently the main biofuel crops in the U.S., but the perennial crops alfalfa, hybrid poplar, reed canarygrass and switchgrass have been proposed as future dedicated energy crops.

Bioenergy crops are able to offset carbon dioxide emissions by converting atmospheric carbon dioxide into organic carbon in biomass and soil, but the production of biofuels requires fossil fuels and impacts greenhouse gas fluxes.

The primary sources of greenhouse gas emissions associated with crop production are soil nitrous oxide emissions and the CO2 emissions from farm machinery, farm inputs and agricultural processes. Colorado State and USDA scientists quantified all of these factors to determine the net effect of several bioenergy crops on greenhouse gas emissions.

Researchers found that, once the DAYCENT results were combined with estimates of the amounts of fossil fuels used to provide farm inputs and operate agricultural machinery and the amount of fossil fuel offsets from biomass yields, they were able to calculate the net greenhouse gas fluxes for each cropping system.

This study was a unique and complete analysis of bioenergy cropping for several reasons. Different crops vary with respect to length of plant life cycle, yields, biomass conversion efficiencies, required nutrients, net soil carbon balance, nitrogen losses and other characteristics which in turn impact management operations. Additionally, crops have different requirements for farm machinery inputs from planting, growing, soil tillage, applying fertilizer and pesticide and finally harvesting.

The researchers were able to use life cycle analyses and the DAYCENT model to account for all of these factors as well as integrate climate, soil properties and land use to accurately evaluate the impact of bioenergy cropping systems on crop production, soil organic carbon and greenhouse gas fluxes.

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