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Farmers and landowners had the opportunity to discuss edge-of-field options with ISU’s Matt Helmers at this meeting last June at Altoona.
ON THE EDGE: Farmers and landowners had the opportunity to discuss edge-of-field options with ISU’s Matt Helmers at a June meeting in Altoona.

Edge-of-field demos hit the mark

Iowa Learning Farms: Conservation Station helps people understand what these practices are and how they work.

By Matthew Helmers

When the Conservation Learning Group and Iowa Learning Farms rolled out the new Conservation Station on the Edge trailer in early 2018, we were hopeful it would get a positive reception and help engage farmers to dig deeper into edge-of-field solutions, such as bioreactors and saturated buffers. It’s exciting to report that for most of the 1,300 Iowans who visited the Conservation Station on the Edge at 24 events this year, the outcome was a success. While we didn’t observe any “Aha” moments or shouts of “Eureka,” we did get a lot of good questions and positive feedback.

Speaking about edge-of-field practices is always a bit of a challenge because bioreactors and saturated buffers work silently out of sight. Once installed, both are underground and not easily observed. This is where the demonstration stations and the graphics designed for this trailer help make the process observable and improve comprehension of the immediate and long-term benefits.

SATURATED BUFFERS: This is one of the edge-of-field conservation practices explained by a visual model as part of the trailer’s display.

Both practices are relatively young in terms of research and application. Field-scale bioreactors have been studied for 10 years, and saturated buffers for about seven. However, there has been heightened interest and increasing media coverage of edge-of-field approaches in recent years.

There’s a natural curiosity among farmers, but unfortunately when they attend a typical field day to learn about these methods, there isn’t much to see but some PVC pipes and boxes sticking out of the ground. The Conservation Station takes away the guesswork by helping them visualize what is happening underground, and this goes a long way toward satisfying their curiosity.

One size fits all?
One comment or question we’ve heard relates to how these practices compare to or fit in with other runoff control and conservation practices, such as no-till, cover crops, grass waterways and prairie strips.

The answer is simple but also complex. No single practice is best for all situations. These edge-of-field structures are relatively new tools in the denitrification toolbox, but they don’t replace or diminish the impact of other methods.

There is no single solution that fits every farm or field, but with more options, farmers have more opportunities to decrease nitrate loss, maintain healthier soil and help ensure a cleaner water supply.

Soil conditions, topography and location are critical considerations in selecting the most effective strategies for any field. For example, saturated buffers can only be installed in fields adjacent to streams.

How does it work?
In simple terms, both of these structures slow the outflow of water from tile-drained fields and promote denitrification by naturally occurring microbes. Bioreactors direct water laterally through a bed of wood chips. The carbon in the wood chips supports the microbial consumption of nitrate. The saturated buffer directs the slowly moving water beneath the buffer to promote denitrification by the microbes in the soil.

BIOREACTOR: This edge-of-field practice is explained, showing how bioreactors function to remove nitrate from water draining underground.

The Conservation Station graphics and models aid comprehension and encourage visitors to ask questions about what they are seeing. Since nitrate is dissolved in the water, there isn’t a visual clue, such as murky water, to show the before-and-after results. The graphics provide visual depictions of what is happening at each stage of the structure, providing an opening to great conversations about these practices.

In the early years, discussions about these processes that slow water outflow typically included concerns about unduly retaining water in the fields or plugging up the tile drain system. Those objections have diminished through better understanding of system design and the bypass outlets, which ensure proper outflow when the water table rises.

Conversations and questions now trend toward cost-benefit trade-offs, and identification of best practices for specific sites.

Is there an ROI?
A frequent question or challenge we heard from farmers pertained to the cost of implementation. In short, there is no direct agroeconomic benefit from installing a bioreactor or saturated buffer. It does not produce incremental income. However, the larger environmental benefits of denitrification are clear: greater diversity of wildlife, cleaner and healthier waterways and movement toward achieving the Iowa Nutrient Reduction Strategy goals.

We encourage you to learn more about edge-of-field practices. Field day and fair season is in the rearview mirror for this year, but the Conservation Station on the Edge will be hitting the road again soon. There are also a wide variety of resources, webinars and podcasts about edge-of-field practices, as well as other farm applications, which have proven to aid denitrification, at

Helmers is professor of ag and biosystems engineering at Iowa State University and faculty adviser to Iowa Learning Farms.

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