Recycling fertilizer? South Dakota State researchers test ways to reduce and reuse runoff from farms

What if you could capture the fertilizer that washed away with the rain and reuse it on your field? A pair of South Dakota State University professors is studying a way to do just that.

Dr. Laurent Ahiablame, from the department of agricultural and biosystems engineering, teamed up with Dr. Srinivas Janaswamy, from the department of dairy and food science.

Ahiablame has worked with edge-of-field nutrient removal methods, namely the woodchip-filled pits known as bioreactors. Bioreactors use microbes and a carbon source to “eat away” the nitrogen that moves with the runoff through the field’s tile drainage system. “They’re a proven technology to improve water quality,” Ahiablame said.

The microbes release nitrogen into the air as a gas and keep it from polluting lakes and rivers, but Ahiablame wondered if there was a way to capture the nutrient and take it back to the field.

Janaswamy had an idea from the food industry. He believes products used to thicken foods such as salad dressings and ketchup could be used to absorb nutrients like nitrate and phosphorus.

The thickeners in the form of beads – fully biodegradable polysaccharides – would help clean runoff water, but they have another major benefit beyond what bioreactors do today. The tiny beads could be spread across the field where it would release the fertilizer again, this time for the plants’ benefit.

“Humans have been using polysaccharides as gelling and thickening agents for generations,” Janaswamy said.

He’s encouraged at the thought that these biomaterials could be used to help farmers feed the world in a way that’s friendlier to the environment and less expensive for producers.

“That is what we are dreaming,” he said.

The professors aren’t sure it will work like they hope, but studies on the beads over the coming years will help determine if it’s possible. The project recently received funding through a new state program.

Money for the project comes from a 50-cent increase in the fertilizer inspection fee. The Legislature approved the new program in 2016, and the South Dakota Nutrient Research and Education Council (NREC) awarded its first round of funding this summer. It’s meant to help improve environmental and water quality through better agricultural practices.

“The main driver is sustainability,” said Bill Gibbons, interim director of the South Dakota Agricultural Experiment Station, which helps administer and manage funding for the NREC. “Farmers are very interested in precise placement of nutrients. If any get lost to groundwater or surface water, it’s money out of their pocket.”

The state money funded three other fertilizer-related studies in its first round. One will come up with new nutrient recommendations for oats, updating 2005 guidelines. Another will compare manure and synthetic fertilizer used on cover crops, studying how they each impact soil fertility, water quality and yields. A third study will assess how microorganisms can be used to minimize nitrogen leaching after cover crops are killed by frost.

More funding will be awarded by the end of the year. So far, all projects are being conducted by South Dakota State University researchers, but the funding is open to any university, state, commodity or non-government organization. Gibbons said there’s preference given to South Dakota-based projects.

It’s important to have money dedicated to precise placement of nutrients because it impacts the environment, which affects everyone, he said.

“Farmers – they’re doing their best,” Ahiablame said. But there’s not a perfect way for farmers to control how much nutrients they’re losing, he said.

The beads could be placed in a plastic-lined bioreactor and be used to clean subsurface drainage. They could also be placed in a shallow trench at the edge of the field to capture surface runoff. Once they absorb the nutrients, the hope is that the beads would be applied to the field like fertilizer. The beads would dissolve and leave the nutrients behind.

“They are completely environmentally friendly,” Ahiablame said.

Studies will begin this year in a lab setting. It will be two to three years before they move to the field.

The study’s first step is to learn how much of the nutrients the beads can absorb. There are many other questions after that: How will the water-soluble beads retain their form? At what rate should they be applied to field when it comes time to reuse the fertilizer? How long will it take them to release nutrients in the field?

The professors are looking forward to finding out.

“We really see a bright future for research in this area,” Janaswamy said.

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