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Saturated buffers reduce nitrogen in agricultural drainage.

In Brief: Every summer, a "dead zone" forms in the Gulf of Mexico. Plumes of oxygen-robbing algae, fed by excess nitrogen from the Mississippi River, kill off marine life and threaten the livelihoods of those who fish the Gulf. States bordering the Mississippi River are putting strategies in place to limit nitrogen from wastewater treatment plants, surface runoff, and agricultural fields. In a new study, University of Illinois scientists have estimated that a new conservation practice, known as saturated buffers, could reduce nitrogen in agricultural drainage by 5% to 10%.

It might not sound like much, given that agricultural drainage represents only a portion of the nitrogen entering the Mississippi River. However, the 5% to 10% reduction would result from inexpensive, passive systems that farmers can put in and forget about, said ASABE member Reid Christianson, research assistant professor in the University of Illinois' Department of Crop Sciences and coauthor of the study.

Saturated buffers are vegetated strips of land, as narrow as 30 feet, between tile-drained agricultural fields and waterways. Ordinarily, the tiles carry drainage water from the fields directly into ditches or streams. With a saturated buffer, the water is rerouted to a perforated pipe installed below the soil surface and parallel to the stream. From the perforated pipe, drainage water flows through the soil of the saturated buffer and into the stream. Along the way, soil microbes remove up to 44% of the nitrogen.

Saturated buffers don't take a lot of land out of production, and they are fairly inexpensive to install, at $3,000 to $4,000 to treat the drainage water from a field-sized area, roughly 30 to 80 acres. "Farmers have to avoid farming right up to the creek, but as an edge-of-field conservation practices, saturated buffers fit easily with farming and provide additional benefits, like wildlife and pollinator habitat," said ASABE member Laura Christianson, assistant professor at U of I and co-author of the study.

To arrive at their nitrogen reduction estimate, the Christiansons and ASABE member Janith Chandrasoma, a doctoral student at U of 1, looked at publicly available digital maps of crop, soil, and stream types to estimate the total number of saturated buffers that could be installed across the Midwest. They estimated that 248,000 to 360,000 buffers could treat up to 9.5 million acres of drained land. With other studies showing average nitrogen removal rates between 23% and 44%, their estimated number of saturated buffers would reduce the total nitrogen load in agricultural drainage by 5% to 10%.

The estimation required several assumptions. For example, there are no satellite images or maps for tile drainage systems across the entire Midwest, so the researchers assumed that corn and soybean fields characterized as poorly drained were most likely tiled. However, Reid noted that tile drainage systems are installed under many corn and soybean fields in the Midwest, and not just poorly drained fields. "Overall, our assumptions were conservative," he said, "We probably underestimated our figures as a result."

Saturated buffers are a new conservation practice, and the first USDA standard was published in 2016. So far, they have not been adopted at anywhere near the scale shown in the Christiansons' study. For example, Laura estimates that fewer than 50 saturated buffers are currently installed across the entire Midwest region. "Adoption at the scale we estimated is likely a long way off," she said, "But anything we can do to reduce nitrogen flowing to the Gulf, especially if it fits easily with current farm management, warrants attention."

For more information, contact Lauren Quinn, ACES news writer and media specialist, ldquinn@illinois.edu; Reid Christianson, reiddc@illinois.edu; or Laura Christianson, lechris@illinois.edu.

"Saturated buffers: What is their potential impact across the U.S. Midwest?" by Janith Chandrasoma, Reid Christianson, and Laura Christianson, was published in Agricultural and Environmental Letters (doi: 10.2134/ae12018.11.0059). The work was funded through the USDA Farm Service Agency.

Caption: ASABE members Laura and Reid Christianson (in tan hats) investigate a saturated buffer in Illinois. Photo credit: UlUC/J.Chandrasoma.

Caption: Illustration of the control structure and diversion pipe in a saturated buffer. Drainage water flows from the field through the control structure and diversion pipe and then into the soil toward the stream. Diagram credit: TransformingDrainage.org.

Caption: A saturated buffer in Illinois as viewed from an unmanned aerial vehicle. The truck is parked by the control structure, which diverts drainage water to flow through the soil (below the mowed buffer) toward the stream. Photo credit: UIUC/J. Buret.
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Title Annotation:update
Publication:Resource: Engineering & Technology for a Sustainable World
Date:May 1, 2019
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