Changing perspectives on drainage03/17/2017 | Water Quality
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By Michelle Jones, environmental communications specialist
Traditionally, subsurface (tile) drainage is viewed as a way to remove excess water from fields. However, by adapting the way drainage is used, it may play a role in reducing nutrient loss and supplying water to crops during dry periods.
During the 2017 ISA Research Conference in February, Chris Hay, Ph.D., Iowa Soybean Association (ISA) senior environmental scientist, explained two primary challenges with drainage.
- Nutrient loss through tile drainage is causing issues across the nation
- Despite excess water in the spring, crop yields are often limited by lack of water in late summer
Both challenges are expected to worsen with current climate trends, he continued.
According to Hay, a multi-state project — titled “Managing Water for Increased Resiliency of Drained Agricultural Landscapes” or “Transforming Drainage” for short — is working to address both issues by retaining drained water at the farm and field level.
“The long-term vision is to change how we think about drainage,” Hay said. “Through this project, the process of designing and implementing ag drainage will be transformed to include water retention and even water recycling.”
According to Hay, water can be stored in the field, at the edge of the field and in ponds or reservoirs. During the conference, other members of the Transforming Drainage project further explained these options.
To store water in the field, farmers can use a practice called controlled drainage or drainage water management.
With this practice, control structures are connected to the drain lines and stop-logs placed within the control structure raise the outlet elevation to hold back water when it doesn’t need to flow freely. When full drainage is needed, farmers can remove the stop-logs. This practice holds water in place for drier periods and also holds back nitrate.
In Minnesota, Jeff Strock, Ph.D., professor with the University of Minnesota, has studied the performance of controlled drainage since 2005 at Nettiewyynnt Farm owned by Brian Hicks.
Strock and Hicks compared controlled drainage to traditional drainage. During this time period, controlled drainage showed a 41 percent reduction in nitrate-nitrogen load, or loss, compared to traditional drainage. Additionally, the yield results were mostly the same between traditional drainage and controlled drainage, however, in a few drier years, the controlled drainage showed a slight yield advantage.
“I had this big grandiose idea of extra bushels, but that didn’t come true,” Hicks said. “It transformed into the environmental impact controlled drainage is having for us. Almost every year, you can take it to the bank you’re going to keep nutrients back on the farm.”
Another option to reduce nutrient loss and slow water movement is a saturated buffer.
With this practice, drainage water is diverted through a perforated tile that runs parallel to a stream or ditch. The water seeps through the vegetative buffer and nitrate is removed through denitrification.
In 2010, Iowa State University (ISU) researchers, including Tom Isenhart, Ph.D., ISU professor in the Department of Natural Resource Ecology Management, installed a saturated buffer at Bear Creek along with several wells to monitor its performance.
Isenhart said results from the monitoring wells showed on average the buffer was removing nearly all nitrate by the time it reached the stream. While there is almost complete removal of nitrate from water in the buffer, during high flow events, some water bypasses the buffer untreated, resulting in a lower overall reduction. Isenhart said the Iowa Nutrient Reduction Strategy states saturated buffers reduce nitrate by 50 percent on average.
Pond and reservoir storage
According to Hay, storing drainage water in a pond or reservoir for reuse is “not a new idea, but it has not seen a lot of adoption so far.”
With drainage water recycling, drain water is captured in a pond and then pumped back into the field — either with a center pivot or through the existing drainage pipe — to irrigate the field during dry conditions.
Kelly Nelson, Ph.D., research agronomist and professor at the University of Missouri-Greenley Research Center, has led controlled drainage and drainage water recycling research in northeast Missouri.
Through his research, Nelson found soybean grain yield under traditional drainage only averaged up to 9 bushel-per-acre more than the undrained control. Soybean yields under drainage water recycling averaged 12 bushel-per-acre greater yield than the undrained control. Corn yields showed an even greater yield response to drainage water recycling.
As the transforming drainage project moves forward, the partners use the data from this research to develop tools for the public. These tools will assist drainage engineers, contractors and farmers when implementing practices in the future.
“The goal of project is to turn research results into usable tools and information and get them out to the public,” Hay said. “It starts with field research and then synthesizing and modeling the data across all 10 states. We take that information to develop decision support tools. Then, we use these tools for implementation and to educate the next generation of drainage engineers.”
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