Feedstock Face-Off

Which system should be targeted to produce biofuels feedstocks in the future—high-input, low-diversity crops such as corn, or low-input, high-diversity systems such as mixed prairie grasses? An ecologist and an agronomist weigh in on the debate.
By Susanne Retka Schill | February 05, 2008
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Different visions of the future for ethanol have sparked a debate from opposite poles of an ecological continuum. On one side are the advocates for producing the maximum yield per acre from corn using intensified high-input, low-diversity systems. On the other end are those who envision cellulosic ethanol feedstocks giving economic value to low-input, high-diversity systems such as mixed prairie grasses. Ken Cassman, director of the Nebraska Center for Energy Science Research, and Oklahoma State University Ecologist Mike
Palmer represented their contrary views during a debate this winter at the American Society of Agronomy annual meeting in New Orleans.

First on Palmer's list in critiquing corn is the concern that more land will be converted to plant dedicated biofuels crops. Sodbusting is likely to create more greenhouse gas emissions and global warming potential than using the fossil fuels it's intended to displace, he says. "Land conversion is not a hypothetical issue," he says. "A record amount of virgin soils are being turned in the Great Plains, largely due to biofuels feedstock production." The concern is not just from the loss of virgin soil, but also the increased soil respiration from tilling grasslands which releases carbon and nitrous oxide, he adds. A second concern Palmer raises is the potential for the dead zone in the Gulf of Mexico to grow as more corn acres are produced in the upper Midwest leading to an increase in the amount of nitrogen leaching into the Mississippi River. "It's an awful lot of nitrogen," Palmer says. "$750 million worth of nitrogen goes down the Mississippi annually. That's more than all the nitrogen being used in sub Sahara Africa." While perennial feedstocks such as switchgrass offer some advantages, Palmer warns that a monoculture of grasses will still be energy-demanding, high-input systems.

In contrast to intense monocultures, Palmer proposes the creation of highly diverse, mixed-grass systems that offer the following distinct advantages:

› Growing more than one species allows available resources to be used more efficiently

› Incorporating nitrogen fixers is relatively easy and many will emerge spontaneously

› Adding of ecosystem services such as flowers that promote pollinators

› Lowering inputs

› Using more plant species stabilizes production

› Eliminating the use of biocides

›Producing a trivial amount of greenhouse gas emissions and sequestering carbon

While critics of the mixed grass systems often argue that mixtures of grasses will end up as a monoculture anyway, as one species begins to dominate a particular planting, Palmer says ecologists call that the insurance hypothesis. "The more species you start out with, the more likely you'll find a winner," he says. "The key point here is that what wins one year is not necessarily the winner the next year or 10 years from now. Having a diverse set of species improves the likelihood of sustained production. The basic thinking behind low input, high diversity is to let nature do the heavy lifting."

Mowed Haylands
As an ecologist, Palmer points out that grasslands have developed through biomass removal whether that's accomplished by fire, animal grazing or mowing. He cited an area in Estonia, a small country in northern Europe, which has been mowed for more than three centuries. "This area has the record highest diversity of plants per square meter, much higher than the tropical rain forest," he says. Similarly, a hay meadow in the White Carpathian Mountains of Moravia in central Europe has been mowed continuously for more than 500 years. The hay is used to feed the horses in metropolitan areas. "This area has 40 species of orchids alone," he says, which is indicative of the ecological benefits of mowing grasslands. Ecologists are concerned about grasslands being abandoned when they are no longer needed for hay, he says. In Oklahoma, eastern red cedar is invading abandoned grasslands near cities and creating new ecological problems by depleting water resources and becoming fire hazards as well as a source of allergens.

In evaluating the two systems—conventional intense cropping systems versus mixed grass systems—Palmer argues that in addition to yield, other factors including nitrogen use efficiency, water use efficiency, energy efficiency, carbon sequestration and other ecosystem benefits should be considered. "Let us use our diverse grasslands as a source of biofuels to protect them, for a sustainable economy and environment," he says.

Maximize Energy Yield
In debating the two points of view, Cassman emphasizes the need to maximize the energy yield per acre in order to meet the planet's ever-expanding energy needs. He doesn't discount the desirability of diversity, however, "I'm often amazed that we try for the perfect and throw out the good," he says. "It may be possible to produce a biofuel with incredibly low carbon intensity that is incredibly green with tremendous potential to mitigate greenhouse gasses on a per gallon basis, but have such a low yield per gallon per acre that you would have to expand both biofuel feedstock production and agriculture in general. The net environmental impact from that expansion could be negative." Furthermore, saying a mixed prairie grass feedstock system for marginal lands would be independent of the food versus fuels debate is misleading, Cassman says. "Even marginal land in areas with good rainfall has the potential to produce food and other agricultural products, including livestock," he says.

Cassman is critical of the attention given to Minnesota ecologist David Tillman's proposal that mixed prairie grass systems would be a good, sustainable biofuel feedstock. Tillman's study was based on a single field experiment on one degraded cropland site, he says. "To make regional or global extrapolation requires testing on a much wider range of soil and climatic conditions, and more rigorous modeling," Cassman says. Palmer agrees that Tillman's study and comments were essentially solid speculation. "It is a launching pad for the real experiments that need to come," he adds.

The attention given to a futuristic vision of mixed prairie grass systems siphons away support for critically needed research on the existing feedstocks, Cassman says. "We need to do research that strives to do two things that are dramatically opposed," he says. "One is to get the highest possible yield of the feedstock per unit area. Second, we need to achieve that with minimal environmental impact." The goal would be to achieve the maximum genetic potential in corn yields by eliminating every source of stress. He sees the need to develop new tools, such as weather modeling for farmers to fine tune their crop management during the growing season. Other elements of an intensified corn production system include discovering the optimal plant population, row spacing, and planting date for each growing region. In 10 years of research on the ecological intensification of corn and soybeans in Nebraska, they've increased yields by 35 percent while at the same time increasing nitrogen efficiency by 30 percent to 50 percent, Cassman says. "It's only just begun, we have to do better than that," he says.

There is promise in the marriage of the biofuels industry with environmental goals that are becoming more widely accepted in U.S. society, and, which Cassman says seem to be happening quickly. "The biofuels industry needs to jump on it," he says. He suggests that with the right policies in place, ethanol plants could pay farmers more or less to the degree that their production systems were contributing to reducing the carbon intensity of biofuels.

Cassman also calls for the biofuels industry to support the allocation of more resources for corn research. "It seems we're putting all our eggs in one basket [supporting cellulosic ethanol projects]," he says. "There will not be a second-generation biofuels system if corn ethanol falls flat. Society will walk away from biofuels. They'll say ‘You told us [corn ethanol] would be good for the environment and it would be cost effective, and now look what happened. And now you want us to continue to fund development of the second generation for the same reasons? Why should we trust you and your scientific judgment?' "

Susanne Retka Schill is an Ethanol Producer Magazine staff writer. Reach her at sretkaschill@bbibiofuels.com or (701) 738-4962.