Prairie grass against global warming?

We all know that a replacement for fossil fuels to power our cars has to be found in a near future. But where will this energy come from? Hydrogen? Biofuels made from soya beans or corn? Researchers at the University of Minnesota think that mixed prairie grasses are a better source for biofuels. They contend that fuels made from prairie biomass are 'carbon negative,' which means that producing and using them will reduce the amount of carbon dioxide in the atmosphere. On the contrary, corn ethanol and soybean biodiesel are 'carbon positive,' meaning they add carbon dioxide to the atmosphere.

We all know that a replacement for fossil fuels to power our cars has to be found in a near future. But where will this energy come from? Hydrogen? Biofuels made from soya beans or corn? Researchers at the University of Minnesota think that mixed prairie grasses are a better source for biofuels. They contend that fuels made from prairie biomass are 'carbon negative,' which means that producing and using them will reduce the amount of carbon dioxide in the atmosphere. On the contrary, corn ethanol and soybean biodiesel are 'carbon positive,' meaning they add carbon dioxide to the atmosphere. The researchers even say that producing fuels from prairie grasses growing on 'degraded' land -- not suitable for agriculture -- could reduce worldwide carbon dioxide emissions by 15%. Other experts are skeptical.

Before going further, it's somewhat ironic -- but irrelevant -- that I chose to talk to you about prairie grass the same day I saw the latest movie of the great Robert Altman, who died on November 20, 2006, "A Prairie Home Companion." If you haven't seen this movie yet, it's time to go -- especially if you ever lived in the Midwest. Highly recommended...

Now, let's look at this research project which was led by David Tilman, professor of ecology at the University of Minnesota and director of the Cedar Creek Natural History Area.

"Biofuels made from high-diversity mixtures of prairie plants can reduce global warming by removing carbon dioxide from the atmosphere. Even when grown on infertile soils, they can provide a substantial portion of global energy needs, and leave fertile land for food production," Tilman said.
Based on 10 years of research at Cedar Creek Natural History Area, the study shows that degraded agricultural land planted with highly diverse mixtures of prairie grasses and other flowering plants produces 238 percent more bioenergy on average, than the same land planted with various single prairie plant species, including monocultures of switchgrass.

The basic reason why biodiversity leads to a better efficiency than monocultures is pretty easy to understand: some plants grow during spring while other grow in other seasons, so they 'complement' each other.

Below is an aerial view of experimental plots at Cedar Creek Natural History Area showing these effects of plant biodiversity on population and ecosystem processes (Credit: Cedar Creek Natural History Area). Here is a link to a larger version of this experiment.

Effects of plant biodiversity

This study has already been widely commented, so I'm just picking a single source of information here. In "Prairies could fuel the future," Nature compares the efficiency of various sources of biofuels.

If you take into account the greenhouse gas emissions produced by growing, harvesting, transporting and converting plants into fuel -- along with the carbon dioxide produced by eventually burning that fuel -- and weigh this against the amount of carbon dioxide sucked up by plants during growth, prairie comes out 6-16 times better than corn grain ethanol or biodiesel.

This is a huge improvement. And it's even better when you consider that prairie grass "can grow on land not suitable for agriculture."

Growing mixtures of plants on 500,000,000 hectares of degraded land worldwide could displace about 13% of global petroleum consumption, and sequester about 15% of carbon dioxide emissions, estimate Tilman and his colleagues.

Unifying farmers worldwide would be a very difficult task, and this is perhaps why Tilman doesn't give any date for such an achievement. Nevertheless, he remains optimistic: "We need to accelerate our work on biomass production and its conversion into useful energy sources. Ultimately, this means we need to start paying farmers for all the services they provide society -- for biofuels and for the removal and storage of carbon dioxide."

For more information, this research work has been published by Science under the title "Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass" (Vol. 314, No. 5805, Pages 1598-1600, December 8, 2006). Here is a link to the abstrac of this paper which made the cover of the scientific journal.

Sources: University of Minnesota news release, December 7, 2006; Charlotte Schubert, Nature, December 7, 2006; and various websites

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