Improving technology to meet goals

August 31, 2023 | Kriss Nelson

As farmers work toward meeting the goals of the Iowa Nutrient Reduction Strategy (NRS), producers will be looking for new and improved technologies for in-field and edge-of-field conservation practices.

The Iowa Soybean Association’s (ISA) Research Center for Farming Innovation (RCFI) is continuing its commitment to finding practical solutions for improving water quality.

“The Iowa Soybean Association understands the Iowa farmer and is doing the research feasible for their land to come up with good, solid solutions to meet goals set by the nutrient reduction strategy,” says ISA President-Elect Suzanne Shirbroun, who farms near Farmersburg in Clayton County.

Drainage water recycling

Recycling drainage water is a promising edge-of-field practice. Research on storing water in a pond or reservoir for irrigation later in the growing season shows hope it will support an addition to the Iowa NRS.

“The impetus behind this practice is that it can be seen as a win-win practice,” says ISA Conservation Design Specialist Chris Hay. “The farmer gets the benefit of increased yields from supplemental irrigation, and there is a water quality benefit from capturing and reusing the water and nutrients instead of letting them go downstream.”

Research shows there is potential to lower nitrogen and phosphorus loads. Studies from Agriculture and Agri-Food Canada have documented nitrogen loss reductions of 40-70% and phosphorus loss reductions of 12-36%.

By implementing a drainage water recycling practice, modeling work done with Purdue University predicts reductions in downstream nitrogen delivery of 24-37% and phosphorus 21-39% in Iowa and Indiana.

Studies are just beginning on the practice’s effects on water quality in Iowa.

“We have more data on yields, and there has been good yield information, so it is encouraging,” Hay says. “Now we are researching the water quality and nutrient load aspects. With sites we have constructed, we can monitor the flow and nutrient concentration to develop the water quality data.”

On a site in Calhoun County, testing show a 72% reduction in nitrates entering the drainage water.

“That reduction is encouraging, but we will need more years of data to get a better handle on what the realistic average is going to be,” says Hay.

Saturated buffers

Further innovation of existing edge-of-field practices, including saturated buffers, is underway. An automated control structure, for example, would combine two practices: a controlled drainage system and a saturated buffer.

The addition of an automated control structure would facilitate drainage management in the field bringing as much water as possible into the saturated buffer to be treated.

Modeling progress

Hay serves in an advisory role for a model being designed at Michigan State University. This model assists in locating saturated buffers and calculating soil types, water drainage and nutrient load.

“We can put that information in and, with the model, have a good estimate of what the nitrate reduction will be for a specific saturated buffer,” says Hay. “We can look at expected costs and benefits — a way to most effectively and efficiently spend the funds we have to install these practices.”

Once they develop the model, ISA will apply it to some watersheds in Iowa.

“We will demonstrate how the model works and what the benefits can be with the hope that it will become a useful tool for future saturated buffer siting,” he says.

Bioreactor management

Iowa State University is conducting research on the feasibility of pumping water into a bioreactor during the summer when drainage stops.

“Bioreactors reduce nitrates during spring drainage, but as we move into summer, things tend to dry up,” says Hay. “When the bioreactor is dry, the woodchips will age and possibly degrade faster. It could be more efficient to keep water running through the bioreactor.”

The research should provide insights on using a drainage ditch, stream or main to pump water into the bioreactor, treating it and putting it back to the water source after it goes through the bioreactor.

“This process keeps the bioreactor efficient, and we’re reducing more nitrates by treating as much water as possible,” says Hay.

Reducing phosphorous

In 2017, blind inlets were added to the Iowa NRS list of practices that can help reduce phosphorus.

Blind inlets replace surface inlets used in a field’s drainage tile system. This practice involves removing the riser in lower or pothole areas of the field.

A grid of perforated pipes is installed in the ground and covered by gravel.

“This allows water to filter through the gravel before it gets to the pipes, so sediment and phosphorus settle out, reducing phosphorus losses from the field that otherwise would have gone straight through the drainage system,” says Hay.

Treatment through oxbows

Oxbows are winding streams, rivers or creeks that have become separated from the main flow of water and, over time, have become filled with sediment.

Oxbows are restored by excavating soil to historic riverbed depth allowing access to ground water and creating deeper pools.

ISA Field Services Program Manager Brandon Iddings notes that 35-54% of water from field tiles is treated when entering a restored oxbow.

To help make oxbows more efficient in improving water quality, water control structures are installed on the downstream side of the oxbow.

“This allows the oxbow to hold more water,” Iddings says. “The more water it holds, the more nitrates are treated.”

Already recognized as a practice in the NRS, ISA teamed up with the U.S. Fish & Wildlife Service, Resource Enhancement Protection, the Iowa Department of Agriculture and Land Stewardship, and the Nature Conservancy to create a resource for conservation professionals or landowners who are on a mission to restore an oxbow.

The Oxbow Restoration Toolkit is a 29-page step-by-step guide available on the Nature Conservancy’s website.

“We’re broadening the conservation folks’ toolbox on how to implement oxbows so they can go out and work for the landowners,” says Iddings.

“The Iowa Soybean Association will continue to be a leader in conservation practices, such as oxbows, and help grow these Iowa Nutrient Reduction Strategy-approved practices statewide.”

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