Leopold Center for Sustainable Agriculture

A drought-resistant crop for our biofuel future

Back to Leopold Letter Fall 2012

By MELISSA LAMBERTON, Leopold Center graduate research assistant

Envision Iowa’s landscape covered with a crop that produces sustainable biofuel feedstock, strengthens the soil and protects water quality. Best of all, this crop can withstand a climate upheaval, creating its own defense against drought.

A Leopold Center grant project led by Robert Horton, ISU Agronomy, and Thomas Sauer, ARS-National Laboratory for Agriculture and the Environment, demonstrates how reconstructed native prairies might provide an ideal crop for biofuel feedstock in the future. The project expands ongoing ISU research at the Comparison of Biofuel Systems (COBS) site in Boone County.

Iowa is famous for its organic-rich soils. Land use that puts millions of acres under annual row crops has resulted in eroded topsoil and poor soil quality. “The soils have less ability to hold plant-available water,” Sauer said, meaning that crops will reach their wilting point faster during dry weather.

The researchers compared the soil beneath plots of prairie (with and without fertilization), continuous corn (with and without a rye cover crop) and a corn-soybean system. They found that prairie plots had eight to 12 times more roots than the corn plots in 2010. “We all know that prairies have lots of roots, but we were slack-jawed at these numbers,” Sauer said. Researchers calculated that 40 to 55 percent of the prairie total biomass occurred belowground, compared to only 3 percent for corn.

“There are profound implications of having all that organic material in the ground,” Sauer said.

Deep-rooted prairie plants create healthier soil: rich in organic matter, with plenty of aeration, good infiltration, stable structure and active nutrient cycling. In addition to optimizing plant growth, these organic-rich soils hold more water, creating a reservoir that plants can draw on during drought. Sauer envisions that prairies might be grown alone or in rotation with row crops so that farmers can take advantage of this benefit.

Prairies also improve water quality by reducing the movement of sediment, nitrate and other pollutants. In 2010, COBS researchers found that when compared to the corn-soybean system, the fertilized prairie plot released 97 percent less nitrate to tile drainage. By reducing nitrate loading to streams and rivers, farmers can protect the health and economies of communities downstream.

Questions remain about whether prairies will produce enough cellulosic biofuel feedstock to compete with grain-based ethanol. Initial results from the COBS experiment look promising. Researchers estimate that a prairie managed with early-spring nitrogen fertilization will produce amounts of energy comparable to the corn-soybean system, although less than the continuous corn system.

“These prairie systems will hopefully demonstrate the importance of restoring native organic matter,” Sauer said.

The Leopold Center funded this project through a 2008 competitive grant in the Ecology Initiative. The COBS program has been funded by ISU College of Agriculture and Life Sciences, Plant Sciences Institute and Biobased Industry Center, Conoco Philips and the U.S. Department of Agriculture.

Back to Leopold Letter Fall 2012