https://phys.org/news/2019-01-nitrogen-pollution-agricultural-drainage.html

Saturated buffers are vegetated strips of land—as little as 30 feet across—between tile-drained agricultural fields and waterways. Ordinarily, tile pipes carrying drainage water from the fields empty directly into ditches or streams. With a saturated buffer, the water is re-routed to a perforated pipe running below the surface and parallel to the stream. Water then flows through the soil of the saturated buffer into the stream. Along the way, soil microbes naturally remove up to 44 percent of the nitrogen.

"Saturated buffers don't take a lot of land out of production, and are fairly inexpensive at $3,000 to $4,000 to treat drainage from a field-sized area (roughly 30 to 80 acres). Farmers have to be willing to not farm right up to the creek, but in terms of edge-of-field conservation practices, I think saturated buffers fit easily with farming and provide additional benefits like wildlife and pollinator habitat," says Laura Christianson, assistant professor also in the crop sciences department and co-author of the study.