CCFB News» October 2024

As a researcher, Andrew Margenot is naturally skeptical of anything that seems “too good to be true.” But he told those attending the Nutrient Stewardship Field Day in Cook County that struvite, an alternative to phosphorus fertilizer, may be both good and true.

Struvite could be beneficial on several fronts including for water quality by reducing phosphorus runoff and providing a phosphorus source for crops as an alternative to more commonly used monoammonium phosphate (MAP) and diammonium phosphate (DAP) fertilizers.

With more research evidence, struvite could eventually be considered a best management practice and be eligible for cost-sharing or nutrient control credits. As a bonus, it can be reclaimed from point sources including Chicago wastewater today and, in the future, other smaller municipalities.

Margenot, a University of Illinois Urbana-Champaign crop scientist, stood in the Cook County field of Smits Farms, which features flowers, herbs and vegetables, at the event on Aug. 28 looking at the tomato plants where struvite is being tested for its effectiveness.

Previous research by Margenot has shown that “In soils with deficient soil test phosphorous, 50-50% struvite-MAP blends appear optimum for maximizing vegetative corn and soybean growth while minimizing soil test phosphorus by up to minus 18%,” Margenot said using a fact sheet produced Illinois Farm Bureau® and Illinois Nutrient Research and Education Council. Ongoing research demonstrates that 100% struvite instead of MAP or DAP can support the same yields for corn, soybean, and wheat across Illinois, based on on-farm trials from LaSalle County to Effingham County.

Seeing struvite research in person was one of the objectives of the Nutrient Stewardship Field Day sponsored by Cook County Farm Bureau, IFB and the U of I in collaboration with the Metropolitan Water Reclamation District of Greater Chicago. It was part of the conversation about reducing phosphorus losses, a goal of the Illinois Nutrient Loss Reduction Strategy.

“It seems too good to be true, but struvite seems almost perfect,” said Margenot, an Institute for Sustainability, Energy, and Environment professor. However, there are a couple of drawbacks. It costs more than other phosphorus sources now- yet the return on investment could be better if less struvite is needed than other phosphorus forms, he said. Also, while the slow release is good for the environment and longer use, it does mean struvite isn’t as effective in soils with extreme phosphorus deficiencies, he said.

The host farmer, Carl Smits, who farms with his son Andrew Smits, using a variety of environment-friendly practices, said he broadcast the struvite on the soil surface under the tomatoes this year because of the tomato stakes, but in the future, he would incorporate the fertilizer by tillage, which is even more effective by allowing the crop roots to dissolve the granules. He said he expects to see benefits from the struvite on the sweet corn he plants in the same spot next year. This is because the struvite dissolves very slowly, and based on Margenot’s research will dissolve 50% in the first year, and the remaining fertilizer dissolving in the second year.

“Whether the plant uses it this year or next year- it’s money in the bank,” he said.

Struvite could help the U.S. become less reliant on foreign phosphorus and could also be an alternative as traditional world phosphorus sources become depleted – though that is likely centuries away, volatility of fertilizer markets favor more domestic production.