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Conservation drainage

Article cover photo
ISA's Chris Hay is an expert on conservation drainage. Farmers will have several opportunities to hear from him this winter. Photo by Joseph L. Murphy, Iowa Soybean Association

By Chris Hay, ISA senior environmental scientist

Subsurface (tile) drainage is an important contributor to crop production in Iowa, but it also provides a pathway for loss of nitrogen from cropland. Conservation drainage is an emerging set of practices designed to maintain the benefits of agricultural drainage while addressing water quality and flow impacts.

Conservation drainage is a critical part of the Iowa Nutrient Reduction Strategy (INRS) for reducing nitrogen losses into Iowa waterbodies. Practices promoted as part of conservation drainage include in-field nitrogen management, cover crops, edge-of-field and drainage system practices as well as land use changes. Practices vary in their nitrogen-reduction effectiveness, site suitability and cost. No single practice can meet the goals of the INRS on its own, so it will take a combination of practices across multiple scales to reach target nutrient reductions.

Edge-of-field and drainage systems will play particularly important roles for cropland with subsurface drainage. Edge-of-field options include bioreactors, saturated buffers, wetlands, shallow drainage and controlled drainage (or drainage water management).

As the accompanying figure illustrates, edge-of-field and conservation drainage system practices have some of the best performance for nitrogen reduction short of land use conversion. With the exception of drainage water management, which is highly dependent on weather, edge-of-field practices generally have less variability (uncertainty) associated with their performance than other INRS options such as nitrogen management and cover crops. Finally, edge-of-field practices are some of the most cost-effective strategies for nitrogen reduction with equalized annual costs of just over $1 per pound of nitrogen removed.

Average nitrate-nitrogen concentration or load reduction as a percentage. Error bars represent one standard deviation above and below the mean.

In 2016, the pace of new edge-of-field installations picked up in Iowa. The Iowa Soybean Association (ISA) focused efforts in the Elk Run and Rock Creek watersheds, as well as contracting with the Iowa Department of Agriculture and Land Stewardship (IDALS) to facilitate site determination and design. Three bioreactors and two saturated buffers were installed in ISA’s watersheds of focus with an additional 13 practices planned.

ISA conducted more than 12 site investigations as part of the IDALS edge-of-field project which began in June. An innovative saturated buffer system connecting seven outlets into three separate distribution lines was installed at the farm of ISA District Advisory Council member Tom Vincent as part of the IDALS project.

ISA remains in the forefront on edge-of-field practices in Iowa, and it is encouraging to see the pace of installations increase. In order to meet the ambitious goals of the INRS, the pace and scale of conservation drainage adoption and innovations to the practices themselves will need to continue to increase and intensify.

There are several opportunities for farmers to learn about their conservation drainage options. ISA is partnering with Iowa State University Extension and Outreach on two upcoming events: The Drainage Research Forum will be held tomorrow, Nov. 15, in Ames and a workshop will be held Dec. 14 in Fort Dodge that will focus on designing drainage practices such as bioreactors, saturated buffers and wetlands. In addition, ISA’s annual Research Conference will have breakout sessions on conservation drainage. The conference is Feb. 6-7 in Des Moines (to register, click here). Chris Hay, ISA senior environmental specialist, will be a speaker at each of these events.

For media inquiries, please contact Katie Johnson, ISA Public Relations Manager at or Aaron Putze, ISA Communications Director at

For permission to republish articles or to request high-res photos contact Aaron Putze at Iowa Soybean Association | 1255 SW Prairie Trail Pkwy | Ankeny | IA | 50023 | US

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