Reducing Run-off Makes Impact In Fields & Watersheds
Producers wanting to reduce soil and nutrients from leaving their fields can look to techniques developed by Iowa State researchers. These practices span the scale from in-field to watershed.
There is a lot of interest in using bioreactors, trenches filled with wood chips, to intercept tile flow at the edge of fields, says Matt Helmers, associate professor of agricultural and biosystems engineering. This emerging technology is being used at about a dozen sites in Iowa treating approximately 60 acres each. He says the bioreactors are getting attention because they are at a scale individual farmers can implement.
Helmers and his colleagues also are researching strategically placing strips of prairie grass into crop fields at the Neal Smith National Wildlife Refuge. The practice can reduce sediment export 95 percent using 10 to 20 percent restored prairie within the row crop system. The research team is working to create demonstration sites around the state in association with the Iowa Department of Agriculture and Land Stewardship (IDALS) and USDA-Natural Resources Conservation Service.
Researchers also are investigating the benefits of including cover crops in row crop systems. Helmers’ research has found reductions in nitrate leaching with a winter rye cover crop, while other research shows reductions in soil erosion and phosphorus loss. “There seems to be a lot of interest in cover crops not only for the benefits for water quality but also the longer term benefits to soil quality,” Helmers says.
These measures have promise, Helmers says, but research suggests that in-field practices alone may be insufficient to achieve the desired reductions in nitrate export.
Research led by Bill Crumpton, associate professor of ecology, evolution and organismal biology, has demonstrated that restored wetlands can substantially reduce nitrate loads if the restorations are strategically placed.
“It’s not just wetland creation, it’s targeted and strategic, so they intercept and remove contaminants,” Crumpton says. A strategically placed and properly designed wetland as small as 10 acres can remove 35 to 90 percent of the nitrates exported from a 1,000-acre drainage basin.
Crumpton’s work provided the technical basis for the Iowa Conservation Reserve Enhancement Program (CREP). This program, sponsored by IDALS and the USDA-Farm Service Agency, provides permanent easements to strategically restore wetlands that remove nitrates from tile drainage water. Over the past 10 years, a total of 72 wetlands have been established through the Iowa CREP with the combined capacity to remove nearly one million pounds of nitrogen each year.
“Iowa farmers have been very accepting of wetland restoration, especially targeted for this purpose, and landowners appreciate the wetlands for benefits beyond nitrate removal, such as wildlife habitat,” Crumpton says.