Long-term study mixes perennials, annuals

By LAURA MILLER, Newsletter editor

Prairies in the Neal Smith National Wildlife Refuge quickly give way to what might be expected in July in central Iowa: an emerald ocean of corn as far as one can see. However, like grass missed by a lawnmower, a few patches catch the eye.

These areas are not an oversight or poorly drained areas that need to be replanted. They are strategically placed prairie strips that are part of a multi-year Iowa State University research project supported by the Leopold Center Ecology Initiative.

Leading the team are ecosystem ecologist Heidi Asbjornsen, Natural Resource Ecology and Management, and water quality engineer Matt Helmers, Agricultural and Biosystems Engineering.

The goal is to mix perennials into a landscape dominated by annual crops to take advantage of the ecological services provided by perennials. Perennials can sequester carbon, provide wildlife habitat, protect soil and water and in the future be a source of biomass for renewable fuels.

"To make these systems work, however, policies may be needed to provide appropriate compensation to landowners for providing ecosystem services that are in line with society’s growing desire for those services," Asbjornsen explained. "We hope this research will help us understand what combination of annual-perennial mixtures and agricultural policies will maximize social, economic and environmental benefits from agricultural landscapes."

The study involves 14 watersheds, ranging in size from 2 to 8 acres. All are within the refuge and managed as restored prairie and for row-crop production by the U.S. Fish and Wildlife Service. Native grasses have been planted in plots representing 10 or 20 percent of the total drainage area in each watershed, and placed at the bottom or midway up the slope.

Baseline measures were taken in 2006, the prairie plantings were done in 2007, and 2008 marks the first full crop season for the project.

Researchers are collecting data on water quality, including runoff volume during rainfall events, quality and depth of groundwater, and the amount of sediment, nitrogen and phosphorous leaving each watershed. They also are measuring changes in biodiversity: bird and insect populations, plant species and composition in the prairie strips and reconstructed prairie, and insect dynamics across different watersheds.

Plant transpiration, soil respiration and total belowground carbon will be determined once the prairie plants have become well-established, in 2010 four years after planting. Asbjornsen said these measures will help determine how perennials affect soil carbon storage, nutrient uptake and water movement in the watersheds.

Before field experiments began, researchers met with farmers and local stakeholders, including government agencies, producer groups and environmental organizations. This stakeholder advisory group has helped researchers in design and management of the experiment so that findings will be most meaningful and applicable to those who could use the results.

"We realized from the start that unless our research addresses concerns and priorities of people who make decisions on the ground, it will be difficult to promote agricultural systems that include perennial plants," Asbjornsen said. "This stakeholder group has provided valuable suggestions and a local farmer has been active in helping us manage the sites."

The Leopold Center provided an initial planning grant and current five-year operating grant. Other major funders include the ISU College of Agriculture and Life Sciences, National Science Foundation and the U.S. Forest Service. The project is guided by a Stakeholder Advisory Committee comprised of representatives from 15 institutions and organizations.