Saturated buffers are key to removing nitrates from tile drainage

This edge-of-field conservation practice is effective, affordable, and easy to maintain.

Lee Tesdell farms 80 acres near Huxley, Iowa, that have been in his family since 1884. To maintain such a legacy, he’s adopted a long-term view of sustainability and strives to make his farm an example of the impact conservation practices have on soil health and water quality.

Tesdell and row-crop operators Mike and Charles Helland work together on the farm’s management, which, over time, has grown to include a no-till corn/soybean rotation, cover crops, a waterway with native grasses, bromegrass buffer strips, a wood chip bioreactor, and prairie strips.

In addition to addressing erosion concerns and a leaky system with excess nutrients in the fields, Tesdell installed a saturated buffer in 2017 as another layer to further improve the water entering his creek.

“The land and creek have benefited because of strong vegetation in buffer strips already and microbial activity even before putting in the saturated buffer system,” Tesdell says.

The farm’s two edge-of-field practices have reduced the nitrogen load into the nearby waterway. The wood chip bioreactor has reduced nitrates by 53%, according to data collected since May 2014. Data collected since 2018 show denitrification with the saturated buffer at 91%.

The power of a saturated buffer

A saturated buffer intercepts tile drainage water before it outlets into a stream. The water is diverted by a water- control structure through a perforated drainage pipe and then pushed through an existing filter strip. As the water drains through the soil profile, perennial plants take up the excess nutrients.

Keegan Kult, executive director at the Agricultural Drainage Management Coalition (ADMC), attests to the effectiveness of saturated buffers.

“Most times, we’ll see denitrification right away, and we have been noticing some higher denitrification rates on well-established buffers,” Kult says. “If a saturated buffer is installed in a new filter strip where we’re just getting that perennial vegetation planted, the reduction rate might not be as high. But we still see a pretty good reduction in those scenarios, because it’s really the organic matter in the soil that makes a difference.”

Ag drainage management coalition and FSA study

This year, the FSA and ADMC released findings of a study after monitoring seven saturated buffer sites across Iowa, Illinois, and Minnesota between October 2017 and August 2018.

According to Kult, the study’s first goal was to add to the current data set and validate the nitrate concentration reduction per field, which averages 41% to 98%, and nitrate load reduction between 10 and 194 pounds.

The second goal of the study was to determine the scalability of saturated buffer sites and the potential impact of a reduced nitrate load.

“We contracted with the department of crop sciences at the University of Illinois. The group did a modeling run for us to try to determine the number of sites that would be available. That’s where the conservative estimate of 46,920 miles of cumulative stream bank suitable for saturated buffers was identified,” Kult says.

In all, that means about 9.5 million acres are potentially suitable for saturated buffers across the Midwest, about 22% of the tile drained landscape. The study found that with this potential, 5% to 10% of the tile-contributed nitrate load could be removed.

How to get started

This is one of those practices that, if you have the right spot, it’s kind of a no-brainer,” says Kult. “It’s relatively inexpensive compared with other practices, as the average cost is $2,000 to $4,000 per site. There’s also not a lot of maintenance that goes with it, so once you have it out there, it should be doing work for you for quite a while.”

State water-quality initiatives, Environmental Quality Incentives Programs, and Conservation Reserve Programs often provide up to 100% cost share.

If you’re interested in getting started with a saturated buffer, Kult recommends staring with your local Natural Resources Conservation Service office to find out which program will work best for you.

Keep in mind that, due to design standards, the NRCS will need to complete a survey of the saturated buffer site, and a finished design won’t just happen overnight.

“It takes about six months to a year for the practice to actually get installed from the time you go sign up for it,” says Kult.

However, once the buffer is designed and there is a window for installation, a contractor only needs about three hours to get the project wrapped up from start to finish. 

Characteristics of a saturated buffer site

Once you kick off the design process, your local NRCS office will help to determine suitability of a site on your farm, which includes the following eight standards.

1. Must have a tile outlet crossing an existing or planned buffer that can be intercepted.

2. Must drain a suitably large enough area to provide sufficient flow and treatable nitrate levels.

3. Buffer must be at least 30 feet wide and planted with perennial vegetation.

4. Loam or clay loam is ideal.

5. Soil must have a high water table.

6. Soil should contain at least 1.2% organic matter to a depth of 2½ feet to support denitrification.

7. Buffer should be lower in elevation than the field.

8. Stream bank should be less than 8 feet high.

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