New Water Quality Practice Offers First-Year Surprises

New Water Quality Practice Offers First-Year Surprises

New type of conservation practice removes nitrate from water flowing in underground field drainage tiles before it reaches streams. Results look promising in first year test in central Iowa.

Researchers working with the Leopold Center for Sustainable Agriculture at Iowa State University report promising results from a new type of conservation practice that removes nitrate from water flowing in underground field drainage tiles before it reaches streams, rivers and other waterways.

Researchers working with the Leopold Center for Sustainable Agriculture at Iowa State University report promising results from a new type of conservation practice that removes nitrate from water flowing in underground field drainage tiles before it reaches streams, rivers and other waterways.

An estimated 500 pounds of nitrate-nitrogen coming from crop fields along a 1,000-ft. stretch of Bear Creek in Story County never reached the waterway this past growing season. Instead, the subsurface drainage water was diverted to an existing riparian buffer along Bear Creek before it reached the stream.

System removed 100% of the nitrate from 60% of the field tile flow

The new practice is called a saturated buffer, in which a shallow lateral line intercepts tile lines before they release water into a stream. The lateral line has control structures that raise the water table and slow outflow, allowing the buffers to naturally remove nutrients such as nitrate and phosphorus.

"One weakness of riparian buffers in protecting water quality is that our extensively tiled farm fields rush the subsurface drainage water right past and through them," says Jeri Neal, who leads the Leopold Center's Ecology Initiative that is funding the study. "As a result, we are not able to take full advantage of the clean water work those buffers are capable of doing." 

Dan Jaynes, a soil scientist at the USDA's National Laboratory for Agriculture and the Environment at Ames and lead researcher for the project, says the system was able to redistribute about 60% of the field tile flow during the first year of data collection at the research site. "The system removed 100% of the nitrate from 60% of the field tile flow," he says. "We figure that 250 kilograms, or about 500 pounds, of nitrate nitrogen was kept out of the stream."

You'd need a lot of these installed at different points along a stream

The saturated buffer was installed in 2010 as part of a multi-year competitive grant project supported by the Leopold Center's Ecology Initiative. Initially, Jaynes had hoped the new system would be able to divert 10% to 15% of the field tile flow, so these first-year results show great promise for exploring the new technology. "You would need a lot of these at different points along a stream to make a difference in water quality, but this is a start," he says.

Jaynes recently presented the initial project findings at a national conference in Minneapolis. He also is a cooperator on a $200,000 grant to install saturated buffers on nine sites in Iowa, Illinois and Indiana to see how they work under different conditions and other conservation practices. The grant is from the USDA's Natural Resources Conservation Service and Jaynes will be working with the Agricultural Drainage Management Coalition, a partnership of companies and organizations interested in conservation drainage practices.

"This is a technology that many people definitely are interested in, and in having more information about how they work," he adds.

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