Fertilized prairies hold promise for future biofuel systems

Friday, September 7, 2012

BOONE COUNTY, Iowa -- Acres of cornfields often come to mind when Iowans consider the nation’s growing demand for biofuel. Native prairies also have a role to play in future biofuel feedstock production that will provide multiple benefits for soil, water and biodiversity, including resilience to climate extremes like drought.

The Comparison of Biofuel Systems (COBS) experiment compares replicated plots of five cropping systems at Iowa State University’s South Reynoldson Farm. The plots were set up in 2008 to look at different ways of producing feedstock for grain-based biofuel and for biofuel made from cellulosic materials such as corn stover or prairie stover (aboveground plant material).

The Leopold Center for Sustainable Agriculture, which contributed grant funding to a soil project at COBS, has published a new brochure about the project. Download the brochure at www.leopold.iastate.edu/pubs-and-papers/2012-09-comparison-biofuel-systems.

The COBS experiment evaluates the economic and environmental performance of conventional corn-soybean, continuous corn, continuous corn with rye cover crop, fertilized reconstructed prairie and unfertilized reconstructed prairie. The corn-soybean system is harvested for grain; the continuous corn systems for grain and stover, and the prairies for stover.

Tom Sauer, an investigator on the project, said that the soils under prairie have high organic matter, giving them the ability to hold more water and withstand drought. He envisions that prairies might be grown alone or in rotation with row crops so that farmers can take advantage of this benefit.

“There are profound implications of having all that organic material in the ground,” said Sauer, soil scientist at the National Laboratory for Agriculture and the Environment in Ames.

The prairie systems in the experiment have the advantage of eight to twelve times more roots than the corn plots. “We all know prairies have lots of roots, but these numbers were jaw-dropping,” Sauer said. Deep-rooted perennial plants hold soil and water, reducing the movement of sediment, nitrate and other pollutants. In 2010, researchers found that the fertilized prairie plot released 97 percent less nitrate to tile drainage compared to the corn-soybean system.

In addition to improved soil and water, prairies foster much-needed biological diversity. Native plants in both fertilized and unfertilized prairies provide refuges for wildlife, songbirds and pollinating insects.

Prairie systems may become an important part of Iowa’s biofuel portfolio because of their multifunctional benefits and the growing need for cellulosic biofuel feedstocks. Estimates from the early years of the experiment suggest that prairies managed with early-spring synthetic nitrogen fertilization may produce cellulosic feedstock that will make comparable amounts of biofuel to corn grain harvested from a corn-soybean system. Continuous corn systems had the highest yields, but offer fewer benefits to soil, water and biodiversity.

Ongoing work measures emissions of carbon dioxide and nitrous oxide, important greenhouse gases. Researchers also will estimate the energy production potential of each system.

Funding for the COBS experiment has been provided by Conoco Philips, ISU College of Agriculture and Life Sciences, U.S. Department of Agriculture, Plant Sciences Institute and the Biobased Industry Center. The Leopold Center provided support for soil research at COBS, led by ISU agronomy professors Robert Horton and Tom Sauer, through its competitive grants program.


Tom Sauer, ISU Agronomy and National Laboratory for Agriculture & the Environment, (515) 294-3416, tom.sauer@ars.usda.gov

Jeri Neal, Leopold Center Ecology Initiative, (515) 294-5610, wink@iastate.edu

Laura Miller, Leopold Center Communications, (515) 294-5272, lwmiller@iastate.edu