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Mitigating agricultural nitrate losses

Ag Water Stewardship: This complex issue has multiple options for producers.

Warren Formo

June 5, 2024

4 Min Read
Field behind wetland
MULTIPLE BENEFITS: Areas great for wetlands are usually less productive crop ground but can provide habitat, as well as being effective at removing nitrates.Kevin Schulz

Reducing nitrogen losses from cropland is often a conversation filled with blame, demands and broader agendas. But if we stick to the basics, don’t we all agree that it is a good idea? For farmers, it may be solely an economic goal, striving to save money on fertilizer. Others may be concerned about drinking water or the seasonal hypoxic area in the Gulf of Mexico.

Research underway across the Midwest makes it clear that there is no single answer to reducing nitrate losses from agriculture, but research is helping identify a list of practices that can contribute. Basic nutrient management practices in the field make a difference. Cover crops, dual cropping and perennials can be effective at changing nitrogen cycling. Beyond the field, nitrate can be removed through engineered water treatment practices.

Matt Helmers, a researcher at Iowa State University, has spent a large portion of his career studying cropping systems, including nitrogen fertilizer practices and how they relate to both productivity and environmental concerns. An engineer by training, Helmers has a practical, problem-solving approach to analyzing nitrogen issues from the basics of good fertilizer management to removing nitrates from water beyond the field.

Helmers was a presenter at the aptly, if uncomfortably lengthily named, Nitrogen: Minnesota’s Grand Challenge and Compelling Opportunity Conference. This was the 10th in a series of conferences created by Fabian Fernández, nutrient management specialist at the University of Minnesota. Co-hosted by the Minnesota Agricultural Water Resource Center, Extension and the Minnesota Department of Agriculture, our planning committee pretty much asks the question, “Should we try to find a shorter name?” And every year we conclude the same thing: that the name captures the complexity of this event.

Helmers’ presentation, which can be found at Minnesota Agricultural Water Resource Center — YouTube, along with other presentations from this and past nutrient management events hosted by our group, provides a summary of recent research on nitrogen mitigation efforts in Iowa. Helmers lays out several data-backed suggestions of things farmers and others involved may want to consider.

Find what works for you

All the mitigation efforts covered in the presentation are effective, somewhere, to some extent. Some even work across a large portion of the Midwest. The challenge is to figure out which one(s) work for you.

In-field practices like cover crops show promise in addressing nitrogen losses by approximately 30%. Drainage water management has also been shown to reduce nitrogen in tile systems. Beyond the field, Helmers shared data on wood chip bioreactors, saturated buffers, riparian oxbows, and his (and my) favorite: wetlands. Again, all of these practices work, somewhere. Some of them are dependent on landscape and as such, do not work everywhere.

Drainage water management, basically a tile system that can be managed to hold water back at times, can be a difficult retrofit for older systems. DWM works best in new tile projects or where old systems are being replaced. DWM requires some additional engineering compared to traditional systems and works best on relatively flat fields.

Wood chip bioreactors provide effective treatment but have not caught on, due to challenges with sizing and concerns about management when the wood chips decompose. Here again, engineering may hold the key to making bioreactors work more broadly. Consider this, bioreactors don’t necessarily need to be right next to the field.

Wetlands provide habitat in addition to being effective at removing nitrates. Reimagining the engineering of drainage infrastructure and identifying areas where water can be stored temporarily shows great potential for nitrate mitigation, while removing very little land from production. In addition, the areas that are great potential wetland sites are often less productive due to excess water.

Helmers also reported on several research sites where drainage water is being captured and then fed back onto farm fields through irrigation. Recycling water and nutrients is not really a new concept, as most farmers can recall years when the late summer turned dry. An inch or two of water at that time would be a game-changer. Across several sites in Iowa, corn yields were increased by about 40 bushels per acre using recycled drainage water. Applying the practice across a large scale is still a few years off — but it is thought-provoking.

About the Author(s)

Warren Formo

Warren Formo is executive director of the Minnesota Agricultural Water Resource Center.

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