Switchgrass, the Mowable Biofuel

This crop promises not only to make fuel but also to help other crops grow by increasing rainfall

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[Sound of computer mouse clicking and Brian Gelder muttering]

Phil Ross: In a tiny windowless office on the Iowa State University campus, engineer Brian Gelder pulls up a map of the U.S. on his screen. It’s a vision of the future.

Brian Gelder: In the high plains, especially in parts of Oklahoma and Kansas, we’re projecting fractions of the county that may reach up to about 45% switchgrass in 2022.

Phil Ross: Nationwide, that adds up to an area about the size of Missouri newly planted in switchgrass. Behind the change is a law that requires 36 billion gallons of renewable fuel to be blended into our gasoline by 2022. Switchgrass is one of the most promising of the biofuel crops.

Rob Anex: So if we’re going to make biofuels, it’s not a little marginal change in the landscape. We’re going to make a big change.

Phil Ross: That’s Rob Anex, also at Iowa State. Their team is creating computer models to predict what this “big change” means for the weather. How do plants affect the weather? Well, when plants breathe out oxygen, it’s saturated with water. This is called transpiration. Switchgrass will grow larger than corn on the same amount of land, but it’ll also transpire more water. That water will go into the atmosphere and come down as rain somewhere else.

[sound of grass blowing]

Phil Ross: It’s sunset in rural southern Iowa, and a spring storm is moving in. The switchgrass, dry beige stems about waist high, bends over nearly flat in the wind. This is what large swaths of Oklahoma and Kansas will soon look like if the models are correct.

[sound of wind, crackling of footsteps on grass; sound of John Sellers talking]

Phil Ross: This field belongs to farmer John Sellers. He’s a sort of switchgrass guru.

John Sellers: That’s the beauty of these native grasses, is they hide all of the nutrients in this plant in the root all winter long.

[sound of switchgrass]

Phil Ross: Switchgrass has many beauties, actually. It’s native, not a food crop, and can grow on marginal land. It’s also highly productive. Near where Sellers lives, an average acre of land produces 4.7 tons of corn but could produce 5 and a half tons of switchgrass. Which could someday mean a lot more ethanol produced. But it’ll also mean a lot more water. Back at Iowa State University, Rob Anex explains the correlation.

Rob Anex: There’s a nice linear relationship there, that if you want more biomass, you’re going to transpire more water.

Phil Ross: For instance, that extra 0.8 ton per acre in southern Iowa? It’ll transpire about 30 000 additional gallons of water into the atmosphere. To see how changing crops could affect the water cycle, the Iowa State team ran a test of their weather model. Climate scientist Chris Anderson explains.

Chris Anderson: We extracted one day in 1980 from it, and that day was February 26th in 1980.

Phil Ross: And on that day they asked a simple question: What if almost all of Kansas, Oklahoma, and the Texas panhandle had been growing switchgrass? How would the summer of 1980 have turned out? Anderson points to a blotch of blue covering western Kansas and Oklahoma.

Chris Anderson: And you can see it’s drawing from this soil moisture level and reducing the amount of soil moisture down there. In this case, it reduced it by about 5 percent.

Phil Ross: And, on a different map, rainfall. There’s a band of yellow and red from Iowa to Michigan.

Chris Anderson: So the crop is putting more moisture in the air. It’s going downwind and it’s creating more storms.

Phil Ross: The team is currently running models of an "alternate past"—how weather would have looked over 25 years if switchgrass had covered as much land as it’s projected to in 2022. They expect to see more rainfall downwind of the switchgrass. They also expect more intense rains, the kind that cause erosion and flash flooding. So, should we be worried? When you ask Rob Anex, he pauses.

Rob Anex: It all depends on how we decide to make biofuels, and the reason that I’m hedging and saying it that way is that there’s lots of different ways to grow biomass.

Phil Ross: Using agricultural waste like corn stover won’t require more cropland or water. And some places have enough water for new crops. Anex hopes policymakers carefully consider the larger picture of biofuels and the water cycle.

Rob Anex: It isn’t that often when society makes big changes in the way they do anything, and so it’s an opportunity to fix things that are currently broken or at least make sure we’re moving in the right direction.

Phil Ross: That is, in the direction of smart policy that conserves both energy and water in the coming age of biofuels. I’m Phil Ross.

To Probe Further

Check out the rest of the special report: Water vs Energy.