A 120-foot-wide ribbon of deep-rooted switchgrass spools along the Yellow Medicine River, a meandering prairie stream that winds through Doug Albin’s Minnesota farm. For decades, this stream-side grass strip has filtered out pollutants in surface runoff from adjacent cropland.
Recently, this buffer’s filtering power got a boost from a new conservation method, called a saturated buffer. The practice diverts subsurface drainage water into the buffer zone through shallow tile. “It works like a giant soaker hose,” says Mark Dittrich, a drainage expert at the Minnesota Department of Agriculture. “The water seeps out of the tile and raises the water table nearly to the surface.” As the nutrient-laden water percolates through the soil, it is denitrified or absorbed by plants.
Albin, of Clarkfield, Minn., is one of 15 Midwest farmers who are testing this new concept. (See his “platinum” conservation drainage plan, Page 8.) The $553,000, multi-state research and demonstration project is sponsored by the NRCS, the Farm Service Agency, and the Agricultural Drainage Management Coalition (ADMC), an industry consortium.
“There are tens of thousands of miles of grass buffers already installed along creeks and ditches” in the Corn Belt, says agricultural engineer and Project Manager Nathan Utt, Ecosystem Services Exchange, Adair, Iowa. “We’re looking at ways to enhance the effectiveness of these existing buffers.”
Last season, saturated buffers were installed on 15 farms in Minnesota, Iowa, Illinois and Indiana — all retrofitted to existing tile systems and grass buffers. The demonstration sites have different topography, drainage designs, soils, cropping systems and buffer characteristics. Researchers are collecting data on flow, N and P in the drainage water, soil conditions and stream bank movement.
“We want to see how this works across different landscapes, soils and climates,” Utt says.
Indiana buffer trial
Kenneth Cain farms sloping ground laced with small streams in west-central Indiana, near Darlington. He heard about using grass buffers to clean up tile drainage water through his excavation business, and wanted to try it.
“Conservation is who we are as farmers,” says Cain, who farms with his son, his brother Terry, and his brother’s three sons. “We want to do the best job we can.” The Cains have adopted a variety of conservation practices, including continuous no-till, field borders, grass waterways, riparian buffers and cover crops.
Last summer, they installed a saturated buffer along a 90-foot-wide strip of switchgrass that borders the Big Slough, a perennial stream.
An outlet-control structure intercepts drainage water from an 8-inch tile main and diverts it into a 4-inch perforated pipe, placed about 60 feet from the stream bank. The 1,000-foot saturated buffer treats subsurface drainage from 35 acres of a 125-acre, randomly tiled field in a corn and soybean rotation. The whole setup cost about $3,000, says Cain, who did the installation himself.
The buffer, which slopes about 0.1%, is 4 feet above the normal stream height. Using the outlet control, Cain raises the water table elevation under the buffer to 1.5 feet.
He’s eager to learn “how much nitrogen we are actually losing from that 35 acres through the drainage system.”
Huge success in Iowa
Results from the first saturated-buffer research site at Bear Creek, Iowa, show significant improvements in subsurface drainage water quality, says Dan Jaynes, a soil scientist at the National Laboratory for Agriculture and the Environment in Ames, Iowa, which developed the technique.
From 2011 to 2013, an average of 50% of total tile flow from a 25-acre field was diverted into the 1,000-foot Bear Creek buffer, Jaynes says. During high flow periods, some water bypasses the buffer and flows directly into the stream to maintain drainage efficiency. “The higher the percentage of water through the buffer, the more nitrogen is removed,” Utt says.
The N load in the diverted flow at Bear Creek ranged from 240 lbs. to 336 lbs. nitrate-N. “All of the nitrate diverted into the buffer was removed in the shallow groundwater under the buffer before it reached the stream,” Jaynes says (see table).
The cost to remove the N: about $1.02 per pound, “comparable to the nitrate-removal cost of constructed wetlands,” Jaynes says. Eventually, saturated buffers might be eligible for conservation payments, Utt says.
There’s “tremendous potential for broad implementation” of this practice, he adds.
“All the producers we are working with are very conservation-minded,” Utt says. “They are excited about the potential of this practice.” Says Cain, “This is a great opportunity to take conservation to the next level.”