Farm Progress

Saturated buffers enhance on-farm conservation efforts

Illinois farmer’s suite of conservation practices and zero fall Nitrogen all target water quality

Liz Morrison 1

March 24, 2016

7 Min Read
<p>This 120-foot wide native grass buffer strip along Mill Creek, in northwestern Illinois, is filtering both surface runoff and subsurface drainage water. Tile water from the adjacent field is routed under the buffer through a 4-inch pipe. As the drainage water percolates through the soil, it is denitrified. In 2015, the buffer prevented 161 pounds of nitrate-N from entering the creek.</p>

Brian Parkinson is helping to mend the mighty Mississippi. The Reynolds, Ill., farmer has invested in a suite of conservation practices aimed at keeping nutrients out of America’s great river.

A longtime no-tiller, Parkinson has installed grass waterways, filter strips and stream buffers to cut runoff. He eliminated fall nitrogen applications and is learning to grow cover crops.

Recently, Parkinson heard about a new way to clean up subsurface drainage water — a saturated buffer — and thought it would fit well on his farm. “I know we’re losing nitrates through the tile system,” he says. “Saturated buffers seem like a practical solution.”

Divert tile water into buffer

Parkinson, who grows corn and soybeans on silty clay loam soils in northwestern Illinois, first read about saturated buffers in a farm magazine. The conservation drainage practice diverts tile water before it reaches the outlet and reroutes it along the length of an existing grass buffer strip.

It works “like a leach field,” says Joe Gates, district conservationist for Rock Island, Ill., Natural Resources Conservation Service (NRCS). Nutrient-laden water percolates through the buffer soil, where microbes convert nitrate-nitrogen into nitrogen gas through natural denitrification. The technique boosts the buffer’s cleaning power, Gates says, allowing it to filter nutrients in both subsurface and surface drainage.

“I thought I had an ideal place to do it,” Parkinson says: a 120-foot-wide, 1,350-foot-long, prairie grass buffer strip along Mill Creek, a perennial stream that flows into the Mississippi River.

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Parkinson installed his Mill Creek saturated buffer in 2013, as part of a multi-state research and demonstration project sponsored by NRCS, the Farm Service Agency and the Agricultural Drainage Management Coalition, an industry consortium. The research — which includes 15 sites in Minnesota, Iowa, Illinois and Indiana — is aimed at defining the soil and landscape requirements for effective saturated buffers.

Parkinson’s saturated buffer is treating tile water draining from about 150 acres of cropland. An outlet control structure on the field edge intercepts a 12-inch tile main and routes water into a 4-inch perforated lateral that runs under the buffer for 720 feet. Once the water table elevation is set at the outlet structure, there’s little maintenance — an advantage for time-strapped farmers, Stewart says. When tile flow is heavy, excess water automatically bypasses the buffer and empties directly into the creek, so field drainage efficiency is not impaired.

In 2015, a wet year, about a quarter of tile water flowing from the field was routed through Parkinson’s saturated buffer, says project researcher Dan Jaynes, a soil scientist at the USDA National Laboratory for Agriculture and the Environment in Ames, Iowa. In drier years, a greater portion of total flow can be treated in the strip. Parkinson’s buffer removed 161 pounds of nitrate-N in 2015. That was about half the load entering the buffer, and roughly 11% of the field’s total nitrate load.


Where they didn’t work

The saturated buffers removed nitrates at 12 of the 15 research sites in 2014 and 2015, Jaynes says. But they did not work well everywhere.

In Indiana, for example, low soil carbon limited the amount of microbial activity and denitrification in the saturated buffers, Jaynes says. The research found that at least 1% organic carbon needs to be present in the soil at a 2.5-foot depth to support denitrification.

In southeast Minnesota, sand layers below the buffers cut the amount of time water was retained in the soil, lowering effectiveness, and showing that a restrictive soil layer is needed to maintain a high water table in the buffer, Jaynes says.

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Even though several saturated buffers failed to remove nitrates, they provided valuable information for improving site selection, says project director Steve Baker, president of Springfield Plastics, Inc., Auburn Ill. “Sites that didn’t perform had commonalities. But we see great potential.”

For example, a well-sited saturated buffer in Hamilton County, Iowa, removed at least two-thirds of the nitrates routed through the grass strip from 2013 to 2015. The portion of total drainage flow that was treated in the buffer ranged from 64% to 100%, depending on rainfall. Over the three years, the buffer removed 301 pounds of nitrate-N that would otherwise have been discharged into the stream.

The take-home: In the correct location, saturated buffers “look very effective and cost-competitive,” Jaynes says. But, like other conservation practices, “in the wrong location, they won’t do much.”

Cost and site selection

Nitrogen removal costs

Parkinson’s 720-foot saturated buffer cost $3,200 — a lot less than other edge-of-field practices, such as constructed wetlands or bioreactors. Average installation cost for all the research sites was $3,700. The cost of nitrate removal ranged from $0.54 to $4.63/lb. N, with an average cost of $2.13/lb. N removed.

“We see many possibilities for adoption,” says project engineer Nathan Utt, Ecosystem Services Exchange, Adair, Iowa. Many Midwest growers already have well-established grass buffer strips on their farms. In some cases, the tile main already runs under the buffer, “so all you need to do is install an outlet control structure. It’s very cost effective.”

saturated buffer

Saturated buffer site selection

The main site characteristics to look for are:

A tile main to intercept

  • Verify the drainage area to ensure that tile flow is sufficient to justify the cost of treatment, generally 15 acres or more.

  • Find and mark all additional tile outlets within the saturated buffer area so they can be incorporated into the design.

A buffer strip

  • At least 45 feet wide with well-established perennial vegetation.

  • Flat: up to two feet elevation change along the length of the buffer is acceptable.

  • Take soil cores to verify adequate soil organic matter levels and the absence of sand or gravel layers within the buffer.

A place for the water to go

  • The saturated buffer doesn’t need to be along a ditch or stream; it could also outlet into a pond, wetland, etc.

  • The receiving water body should be at least 3 feet lower than the buffer.

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New tools make contour planting more practical

Despite decades of continuous no-till, Brian Parkinson still sees erosion from the planter on his sloping fields in northwestern Illinois.

Contour planting reduces runoff and soil erosion by as much as 50% on slopes, compared to up-and-down-hill planting, according to the Conservation Technology Information Center. But as planters widened, it became hard to achieve consistent seeding rates on contours, so most growers abandoned the traditional practice.

Now, new planter technology is again making it practical to orient rows to topography, instead of the compass and field boundaries, says Parkinson, who farms near Reynolds, Ill.

Thanks to GPS and planters equipped with electric-drive systems for each seed meter, growers planting on contours can now seed the correct population in every row. That avoids both expensive over-planting on the inside rows of contours and on headlands, and under-planting on the outside rows, Parkinson says.

“This could allow contour planting to come back as a stewardship practice.”

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