Leopold Center for Sustainable Agriculture

New systems protect against sediment loss

Back to Leopold Letter Fall 2008

By LAURA MILLER, Newsletter editor

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 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.

Back to Leopold Letter Fall 2008