Leopold Flood Lessons '08: Perennials key in reducing sediment loss

LEOPOLD FLOOD LESSONS '08: PERENNIALS KEY IN REDUCING SEDIMENT LOSS

AMES, Iowa -- Preliminary data from a Leopold Center-funded project shows that perennial prairie strips planted at critical points in fields of corn and soybean have minimized soil erosion, even during periods of heavy rainfall.

“We measured significant reductions in sediment loss with systems that have 10 and 20 percent perennial vegetation on the landscape, compared to systems that do not,” said Iowa State University ag and biosystems engineer Matt Helmers. “These perennials are 15 months old and while they are fairly immature as a native prairie, we are seeing that the standing vegetation, whether prairie plants or mixed with annual weeds, is helping to slow the flow of water from crop fields and as a result we are seeing deposition of sediment.”

The project involves 14 small watersheds within the Neal Smith National Wildlife Refuge in Jasper County that are managed as restored prairie and for row-crop production. 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.

During a three-month period from April to June 30, the average sediment loss from watersheds with no prairie strips was 8.5 tons per acre, compared to an average one-half ton/acre sediment loss on the watersheds with prairie plantings. The period included 10 runoff events that produced measureable sediment loss.

“Our biggest rain event in June was 4-5 inches one morning,” Helmers said. “This resulted in significant runoff through our flow measurement flumes. In areas without prairie plantings, sediment was deposited 4-6 inches deep in our flumes. In contrast, we saw much less sediment deposited in the flume from the watersheds with prairie plants and observed sediment deposits at the upstream edge of the prairie plantings.”

Helmers said many conditions of the past summer may not be typical of other years. “I am convinced these systems can work because they provide resistance to flow and better infiltration, as well as add diversity to the landscape,” he added.

The Leopold Center Ecology Initiative provided an initial planning grant and current five-year-operating grant for the project. More information about the project, including a short video segment, is on the Ecology Initiative web page, www.leopold.iastate.edu/research/ecology.htm.

"We are interested in seeing how we can mix perennial in a landscape dominated by annual crops to take advantage of the ecological services provided by perennials, and still have a system that is profitable for farmers," said Ecology Initiative leader Jeri Neal. "Perennials can sequester carbon, provide wildlife habitat, protect soil and water and in the future be a source of biomass for renewable fuels."

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. These measures will help determine how perennials affect soil carbon storage, nutrient uptake and water movement in the watersheds.

Other major funders include the ISU College of Agriculture and Life Sciences, National Science Foundation, the U.S. Forest Service and Iowa Department of Land Stewardship. The project is guided by a Stakeholder Advisory Committee comprised of representatives from 15 institutions and organizations.