Growing cellulosic feedstocks on federally subsidized conservation land could balance the biofuels emissions equation to be completely carbon-neutral, a study suggests.
For conventional bioenergy feedstocks like corn and soy, using a no-till method to remove weeds can shrink the number of years needing to balance the carbon budget by one-third.
The research is centered on the Agriculture Department's Conservation Reserve Program, a voluntary program that rewards farmers who save a portion of their land for conservation of watersheds and wildlife. In past years, the number of acres enrolled in the CRP has dwindled from a peak of 36.8 million in 2007 to 31 million today, according to a Farm Service Agency spokesman. Rising prices for conventional crops have lured farmers back into production farming, with significant consequences for overall greenhouse gas emissions in the United States.
"Incentives for permanent no till and especially permission to harvest CRP biomass for cellulosic biofuel would help to blunt the climate impact of future CRP conversion," states the study's abstract, published in this week's Proceedings of the National Academy of Sciences.
Most importantly, it provides a market income to farmers. This could encourage them to keep land under the CRP that may have gone to growing crops through conventional methods. This hinges, however, on cellulosic biofuels' ability to become profitable.
"Farmers will rationally want to maximize their economic returns on their land," said Philip Robertson, one of the study's authors and a professor of ecosystem science at Michigan State University. "As the price of corn stays high ... there will be more pressure on the farmer to turn that into cropland."
Balancing the carbon budget
"One might hope that a market in cellulosic will develop quickly enough," he added. That market, once touted as a win-win solution to the thirst for alternative fuels, has been subject to increasing pessimism. U.S. EPA has suggested drastically lowering the cellulosic target in the renewable fuels standard, which sets biofuel goals for 2022. Critics say the technology to turn fibrous, waste plant matter into fuel has been much slower than industry projections (ClimateWire, July 29).
As a renewable source of energy, biofuels have suffered ongoing criticism for their hefty carbon debt. Like bankers do for financial debt, climate scientists assume that the greenhouse gas expense of burning biofuels will be paid back eventually as the crops that make fuel "earn" carbon through sequestering it throughout their life cycle.
But biomass energy critics say this doesn't happen fast enough to really offset the greenhouse gases. It could take up to 100 years for bioenergy acres to pay off their debt. In addition, changing the land use from wild grasslands to cropland can minimize the carbon benefits of biofuels (ClimateWire, April 6).
Growing cellulosic feedstocks, however, neutralizes the carbon debt, said lead author Ilya Gelfand, a researcher at Michigan State University's Kellogg Biological Station. The land use doesn't change, and the reduction of fossil fuels adds to the climate mitigation potential.
"However, I need to say that we are not including indirect land-use change, and [have] intentionally restricted our analysis to make our findings less uncertain," he said. Indirect land-use change refers to the opportunity lost had the biofuel feedstock acres been set aside for other uses.
Digging up emissions
Given that farmers have taken on conventional farming in favor of keeping conservation land fallow, the scientists also looked at reducing emissions through no-till methods. Research has indicated that no-till methods could reduce emissions of nitrous oxide -- a gas with 300 times the greenhouse potency of carbon dioxide -- by 57 percent (ClimateWire, Jan. 6).