STREATOR, Ill. - Researchers have acknowledged since as far back as 1976 that struvite —magnesium ammonium phosphate — utilized as a fertilizer encourages greater growth of grass, fruit and various crops compared with conventional fertilizers. Struvite was found to be especially suited for fertilizing turf grass, not only providing adequate nitrogen and phosphorus, but also magnesium, the vital element of chlorophyll, which is responsible for the green coloration of plants. 

With nitrogen and phosphorus in wastewaters and waterways a burning environmental issue, the idea of recovering crystallized struvite from municipal wastewater plants for use as a phosphate fertilizer is again gaining traction. Currently, an on-farm trial at the David and Jim Isermann farm in LaSalle County, Ill., is examining using struvite as an alternative to traditional phosphorus field applications. 

“Struvite adoption essentially mitigates the phosphorus loss from nonpoint sources, which according to the Illinois Nutrient Loss Reduction Strategy is around a 20 percent contribution to total phosphourus losses,” said Neha Chatterjee, a PhD student at the University of Illinois and lead researcher of the study, which examines the agronomic and environmental impact of a waste-recovered slow release struvite. “Also, (research shows) struvite as a phosphate fertilizer can reduce nonpoint losses of P significantly.”

Specifically, the research— now in its second year — shows that in soils with adequate to high amounts of phosphorus, corn yields are unaffected by up to 75 percent struvite substitution for MAP, while double-cropped wheat and soybeans are unaffected by up to 100 percent substitution.

“It’s just as effective as any other form of phosphorus,” said David Isermann, who is the president of the LaSalle County Farm Bureau. “I think that it’s going to be something we can look at in the future as a way to utilize that phosphorus that would otherwise be lost.”

According to Julie Hewitt, executive director for the Illinois Nutrient Research and Education Council (NREC), struvite is beneficial as a fertilizer in part because it “closes the loop” of getting water from treatment plants to farm fields.

According to a 2014 study by Arabian scientists, its slower nutrient leaching loss and fertilizer quality make struvite an eco-friendly fertilizer. But according to a March 2020 study released by the Soil Science Society of America, the low water solubility of struvite is thought to limit its agronomic utility as a phosphorus fertilizer compared with highly soluble phosphorus fertilizers. 

“Furthermore, struvite’s fertilizer potential is complicated by its hypothesized soil pH‐dependent solubility, crop‐specific interactions, and limited availability of struvite‐derived nitrogen, which may explain conflicting reports of crop responses to struvite compared with conventional phosphorus fertilizers,” according to the study.

“Struvite‐fertilized plants yielded higher biomass, phosphorus concentration, and phosphorus uptake compared with ammonium phosphates, and superphosphates in soils with pH < 6 and crop responses decreased with increasing pH,” the Soil Science Society study found. However, “evaluations of struvite collectively indicate its efficacy as a phosphorus fertilizer is affected by soil pH and its contribution to total nitrogen application.”

Jean Payne, president of the Illinois Fertilizer and Chemical Association, said that struvite-based fertilizers are not yet readily available to farmers at the retail level. “I am aware of this research,” Payne said. ”Currently most of the struvite fertilizer goes into the specialty market but I do think the more this process is perfected, the possibility of it being available in bulk exists.” 

An update from the Isermann on-farm struvite study kicked off the second in a series of “virtual field days” offered online courtesy of the Illinois Farm Bureau’s Nutrient Stewardship Grant Program. A video and booklet from the presentation can be viewed at https://on.ilfb.org/30X0a0K.