New report shares latest research on potential for ag drainage water recycling
What if Iowa farmers could collect field drainage and rainfall to supply the right amount of water at the right time for crop production – and improve water quality in the process? That dream is coming closer to reality, thanks to the emerging technology of drainage water recycling (DWR) already in practice on several Iowa farms.
Precipitation in Iowa is generally adequate to produce good crops. However, yields are often limited when the timing and volume of rainfall doesn’t coincide with crop water needs. By storing drainage water in the spring to reuse in the summer as supplemental irrigation during dry periods, DWR can increase crop yields and make cropping systems more predictable and resilient to weather extremes.
DWR in Iowa
Farmers who want to learn about DWR systems can download a free report, Drainage Water Recycling for Crop Production and Water Quality in Iowa,from the Iowa Soybean Association (ISA) website. The new eight-page publication updates the status of research on the practice in the state and region and was written by consultant Chris Hay, formerly with the ISA, and Matt Helmers, professor of agricultural and biosystems engineering at Iowa State University and director of the Iowa Nutrient Research Center.
The new publication reviews information from seven sites across the Midwest and adds new findings from three drainage water recycling systems in Iowa. One of these was installed in 2022 by Kellie and A.J. Blair on their corn and soybean farm near Dayton, Iowa. There, a corner of a field was excavated to create a small reservoir that can irrigate about 106 acres of adjacent farmland.
“We are already experiencing more unstable weather and know this may become a greater concern in the future, so we wanted to be prepared,” Kellie said. “We also had the chance to work with researchers interested in monitoring this kind of system in our area and thought that would be a good opportunity. We’ve only had one year of operation so far, so it will take some time to know how well it is going to work and pencil out.”
Water quality
Improving water quality was another reason the Blairs invested in the DWR, Kellie said.
Drainage water recycling systems can capture excess nitrogen and phosphorus from farm fields that would otherwise flow downstream with drainage water. Storage in a reservoir can reduce the concentrations of those nutrients and allow them to be recycled back onto fields with irrigation. Depending on how systems - and the land surrounding them - are designed and managed, they may also provide additional benefits, such as habitat for migrating waterfowl.
Four “site-years” of monitoring in Iowa showed dramatic reductions of nitrogen, ranging from 92% at the Dayton site to 63% at the Lake City location. At the latter site, where more water flows through the system, higher total loads of nitrogen were treated despite the smaller percentage reduction.
Generally, phosphorus was reduced as well, though the story there was more complicated. At Lake City, the 2022 data showed that phosphorus increased in water flowing back to the stream, yet the next year, phosphorus loss decreased. These results are a focus of continued research, according to the authors.
Benefits and costs
Drainage water recycling systems are not cheap or suitable for every situation. They usually require new underground drainage lines in fields and some type of irrigation equipment. Most locations will also need excavation for a reservoir. If a stream will be impacted, permits may be required.
Yields from irrigated portions of fields with drainage water recycling systems were consistently greater than from the rainfed areas. The site in Iowa with the longest production record showed corn yields improved by about 35 bushels per acre greater on average.
“Drainage water recycling is not a new practice,” Helmers said. “Early research in Iowa from the late 1980s and 1990s showed that these systems have promise, but due to the costs, it was suggested that the greatest potential for the practice was for high value crops or areas where there were significant water quality concerns. We believe that the potential for these systems is increasing with concerns over water concerns increasing and modeling that suggests water recycling will become more profitable over time.”
Hay agrees. “There are still unanswered questions before we can recommend scaling up. They include getting a better understanding of likely long-term payoffs. Even so, the new report provides more evidence that these systems can deliver ‘win-win-wins’ for production and environmental benefits that we don’t always have.”
To get a better idea of the potential for drainage water recycling at the landscape scale, Hay and ISA have been working with the engineering company ISG on a feasibility assessment for four areas of Iowa. Several locations are being considered, and new funding proposals are being developed to support future research.
This work was supported in part by the Iowa Nutrient Research Center, the Iowa Soybean Association and the Iowa Department of Land Stewardship with support from the EPA Gulf of Mexico Office.
