Surprising Results in Ag Runoff

Janice Kasperson - Erosion Control Editor

It’s well established that nutrients in stormwater runoff—nitrogen and phosphorus—lead to algae blooms, eutrophication, and dead zones in water bodies. Some of the nutrients come from urban runoff, including overfertilization of landscaping. A great deal more of them come from agricultural lands.

Although stormwater from urban areas is generally regulated through NPDES permits, agricultural operations, with a few exceptions, are exempt from such regulation. Instead, there are several voluntary conservation programs in place to encourage farmers to manage nutrients more responsibly, and ongoing federal research to help determine which steps—such as widely encouraged no-till farming—actually lead to improvements in water quality.

How effective are these measures? At a recent meeting of the Ohio Farmers Union, a researcher with the US Department of Agriculture presented some unexpected and frankly kind of discouraging results. Mark Williams, a USDA soil drainage researcher, reported that his agency has been testing runoff from individual farmers’ fields, including tile drainage. Although no-till farming reduces sediment loss and surface phosphorus loss, he said, it appears to increase the dissolved phosphorus in the tile drainage.

On the face of it, this is bad news; something USDA has been recommending and that many farmers have been voluntarily practicing is now showing a less-than-beneficial result. But because we now understand better the mechanism by which the increased phosphorus occurs, there may be ways to fix it. Williams explained that although phosphorus concentrations are actually higher on the surface, the volume of water flowing through the tile drains is greater than the volume on the surface, and therefore more phosphorus is leached out. No-till farming allows the nutrients to infiltrate slowly, but they aren’t well incorporated into the soil, instead following natural cracks, pores, and fissures and therefore washing out quite easily. Tilling the soil, on the other hand, would incorporate the nutrients into the soil better and result in less nutrient loss.

The solution, he said, is not necessarily to stop the no-till practice, but to find ways of incorporating nutrients so that they stay put—perhaps through subsurface injection, which USDA is now researching. You can find more details here.

At the same meeting, Ohio’s state conservationist, Terry Cosby, announced upcoming federal funding to help establish demonstration or “discovery” farms at which farmers can see firsthand how various conservation practices work and which ones might be a good fit for them. Researchers will be testing “about every practice that we offer” at the demonstration farms, he said, as well as providing additional resources to help farmers manage nutrients.

What has your experience been with voluntary programs such as these? EC_bug_web

  • Philip Massirer.

    Where can I obtain a copy of this research? I am interested in finding out more details. Thanks.


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