Emerging drainage water recycling practice could improve yields, water quality

Illustration showing drainage water recycling system with overhead pivot irrigation and reservoir
Illustrations of two types of drainage water recycling systems, overhead pivot irrigation (above) and subirrigation (below). Courtesy of TransformingDrainage.org.

AMES, Iowa — Drainage water recycling (DWR) is a drainage management system designed to capture water during wet periods so it can be used later when growing crops are thirsty.

Versions of DWR have been around for years, but adoption has remained limited. Now, interest is growing as the practice is recognized for its potential to improve water quality and help farmers reduce risks from weather volatility.  

Research underway by the Iowa Nutrient Research Center (INRC) and the Iowa Soybean Association is analyzing drainage water recycling’s costs and benefits, with funding from the Iowa Department of Agriculture and Land Stewardship, the INRC and the USDA National Institute for Food and Agriculture.  

“Too much rain or not enough rain are two of the biggest problems for Iowa crops most years,” said Chris Hay, senior research scientist at the Iowa Soybean Association. “Drainage water recycling can help farmers address these challenges. Research -- mostly done in other states -- shows it can boost yields by up to 50% for corn and 30% for soybeans. Our early work modeling it here in Iowa also shows potential for significant yield gains, especially in dry years, and the system can also benefit water quality and wildlife. But there’s still a lot of work to be done to predict what farmers can expect in terms of return on investment.”

In addition to modeling predicted results at several Iowa locations, Hay and Matt Helmers, INRC director and professor of agricultural and biosystems engineering at Iowa State University, will soon be gathering in-field data at three sites. Locations in Calhoun and Webster counties are in the planning and installation phases. The team already has two years of monitoring data from a Story County location on Woodland Farms, Inc., owned by the Hermanson family, who started using drainage water recycling several years ago.

According to Nick Hermanson, who farms with his cousins, the family has two types of DWR systems, which they installed “after one of us read about the idea and decided to experiment.” Their first system uses subirrigation, capturing and storing drainage below-ground, feeding the saved water back to the crops through tiles when conditions are dry. The other system uses more conventional overhead pivot irrigation that draws water from a pond. They can also use water from a nearby creek if water levels are adequate.

“Both systems have their advantages,” Hermanson said. “The subirrigation system was expensive, but it works great with little maintenance. The center pivot was a lot cheaper, but it takes considerably more management.”

Hermanson, an Iowa State grad, said he happened to mention the family’s DWR experiment to his one-time advisor Matt Helmers, a researcher with expertise in drainage water management. Coincidentally, Helmers was looking for a DWR system to monitor and the Hermanson farm is only a few miles from campus. Monitoring started in 2019.

“Studying the Woodland Farms’ DWR system has provided a unique opportunity to gather preliminary data to help plan other sites,” Helmers said. “Our early findings show that DWR can have multiple benefits, including significantly reducing nutrient delivery to water downstream. On the other hand, the costs are relatively high, and the systems are not going to be needed every year. It confirms findings that DWR systems are going to be most favorable for higher-value crops and where water quality is a big concern. To bring the practice to more Iowa farms, at least in the near future, new conservation incentives may be needed.”

At this time, drainage water recycling is not listed on the menu of conservation practices in the Iowa Nutrient Reduction Strategy.

“That could change before too long, depending on our research findings,” Helmers said. “We need more data, but we expect the practicality and payoff will depend a lot on the site. The benefits are likely to be the greatest in areas that are highly drained. On individual farms, the payoffs will depend on factors such as whether there is already a farm pond that can be utilized. If a new reservoir would be required, how easy would it be to build one near good cropland?”

To help landowners and drainage contractors evaluate DWR systems, the researchers, in cooperation with partners at Purdue University, have introduced a new tool, Evaluating Drainage Water Recycling Decisions (EDWRD), available at TransformingDrainage.org. The website also includes additional resources and peer-reviewed materials by Hay, Helmers and others.

For the Hermansons, the decision to try DWR was inspired by watching area land prices continue to escalate. “Every farm is different, but we decided it made sense for us to invest more in the land base we already have and try to make it more productive and profitable. I’m really curious about what the nutrient data will show over time, but we’ve already seen yield benefits from our systems. Not every year, but we’re sold based on the years when it has provided dramatic improvements.”

The Iowa Nutrient Research Center pursues science-based approaches to evaluating the performance of current and emerging nutrient management practices, providing recommendations on implementing the practices and developing new practices.

Illustration showing drainage water recycling system using subirrigation through drainage tile.