Struvite offers farmers phosphorus source

CHICAGO HEIGHTS, Ill. — Struvite is a phosphorus fertilizer that dissolves in the presence of plant roots.

“Whether it is applied months ahead or weeks ahead it won’t matter, which is important for nutrient losses,” said Andrew Margenot, associate professor at the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois.

“We have been doing research work with Carl and at other sites in the state using struvite, some of them as far back as 2018, to try to understand the potential,” said Margenot during a Nutrient Stewardship Field Day hosted by Illinois Farm Bureau at Smits Farms, owned by Carl and Deb Smits.

“There’s been estimates across the Corn Belt, if we recycle all the phosphates out of the human and livestock waste stream, there’s enough phosphorus in circulation to never have to buy phosphorus inputs again,” the professor said.

“If you can retrieve the phosphate out of the wastewater treatment plants and use it as a granular fertilizer on fields in a way that is less water soluble, then that same lack of being dissolved makes it less susceptible to being dissolved with rainwater in the field to reduce runoff losses,” he said.

Margenot has researched struvite on over 13 on-farm trials with tomatoes, corn and soybeans.

“We found that yields are the same compared with conventional MAP or DAP,” he said. “In some sites we see a yield increase in soybeans and we think the magnesium is boosting yields in southern Illinois because those soils have less magnesium.”

With tomatoes, Margenot said, the research has shown that struvite helps to immobilize lead.

“We know there is a lead problem in Chicago urban soils and the phosphate binds up the lead and makes it less accessible for the crop to take up,” he said. “So, we can use phosphates to reduce lead contamination.”

“Andrew asked me to do a trial and I was happy to do it,” Carl Smits said. “Struvite flows so it can be spread with a regular fertilizer spreader.”

The trial was done on Smits Farms in 2024. There were three treatments — no struvite, 517 pounds per acre of Struvite and 1,034 pounds per acre of struvite on tomatoes and soybeans.

“We spread it during R1 when the beans were probably 18 inches tall and we did not incorporate it,” Smits said.

“We got a 5 bushel per acre increase on the soybeans with the struvite versus no struvite,” he said. “And it didn’t matter whether it was 517 or 1,034 pounds of struvite.”

Smits does not have data for the number of pounds of tomatoes produced in this trial.

“The only data I have is visual and the control tomatoes were OK,” he said. “But the plants that received 517 or 1,034 pounds of struvite had more flowers than the control.”

The farmer hopes to do another trial with struvite on his farm in Cook County in northeastern Illinois.

“We were looking forward to doing it in 2025, but we couldn’t get it worked out this year so we’re looking forward to 2026,” Smits said.

“Struvite is a good product, it’s locally made, it allows the phosphorus cycle to be circular instead of linear and it’s good for the crop,” he said. “It doesn’t have any negative effect on the soil and it helps remove waste from water, so I think it’s a win.”

Smits plans to incorporate the struvite next year instead of applying the fertilizer on top of the ground.

“I think there will be a bigger boost to put struvite where the roots are,” he said. “Rain helped, but moving forward I think we have to incorporate it.”

The farmer purchased the land in 1990 at Chicago Heights where he now grows herbs, vegetables and flowers.

“We started when the landscape waste ban went into effect,” he said. “We’ve been taking landscape waste for 35 years.”

On the farm, Smits has a pile of yard waste and another pile of wood chips.

“There is an incredible amount of organic waste that is unutilized and could be used on farms,” he said. “You cut your grass, trim your bushes or rake your leaves. We take all of it and grind it.”

Smits encourages anyone with the opportunity to use landscape waste.

“Get it on your fields because organic matter is your friend,” the farmer said.

“When everything is done growing in the fall, we spread the landscape waste on the entire farm with a manure spreader,” he said.

“Our ground is flat, so there is no erosion here,” Smits noted. “We moldboard plow because we have to get the yard waste into the soil where the microbes are.”