Soil additive devised by Penn State researchers may cut farm phosphorus runoff

UNIVERSITY PARK, Pa. — When farmers apply poultry litter — chicken manure — to fields as fertilizer, it adds nutrients to the soil like phosphorus that plants need. However, phosphorus can dissolve in water and runoff into streams instead of going into crops, causing water pollution and economic loss for farmers, according to the U.S. Department of Agriculture. That’s a huge problem in watersheds like the Chesapeake Bay, where farmers raise hundreds of millions of chickens each year. In an effort to reduce phosphorus runoff, a team led by Penn State researchers recently demonstrated that the use of a novel soil additive might be effective.

The additive — RhizoSorb, a patented soil-fertilizer product designed to greatly increase phosphorus fertilizer efficiency — was born from research in Penn State’s College of Agricultural Sciences. Applied with fertilizer, it reduces phosphorus runoff, saves farmers money by leaving more fertilizer in the fields for crops, lowers greenhouse gas emissions and enhances crop uptake. In a new study, the researchers tested whether its active ingredient — a modified aluminum oxide blend that binds phosphate to its surface — could reduce soluble phosphorus losses from agricultural fields that receive poultry litter applications.

The researchers found that adding RhizoSorb to fields before applications of poultry litter reduced water-extractable phosphorus — the phosphorus most likely to run off in rainwater — by 26% to 53%. They recently published their findings in Agricultural and Environmental Letters.

Study senior author and team leader Charles White, associate professor and extension specialist in soil fertility and nutrient management at Penn State, explained that in this context, Rhizosorb essentially detains phosphorus in the poultry litter.

“Rhizosorb is commercialized around using it with a phosphorus fertilizer as a way to modulate the availability of phosphorus so that its efficiency is improved and losses are reduced,” he said. “But this research is unique in that we used that same active ingredient, the aluminum oxide material, as a way to manage phosphorus losses from manure.”

Pennsylvania, which has a massive animal agriculture industry, has a long-standing problem with phosphorus losses from manure applications, White pointed out. Phosphorus losses used to be associated mostly with erosion of soil particles, he said. But now that the state has so much no-till farming — an agricultural technique for growing crops without disturbing the soil through plowing — there is an increasing issue of soluble phosphorus losses that occur when manure and fertilizer are left on the soil surface.

“In no-till, manure is placed on the soil surface where it's very vulnerable to run off with water,” White said. “So, this research is novel and potentially very important because it takes this active ingredient that was primarily designed and commercialized around fertilizer management and uses it in the context of a manure system.”

In the study conducted at Penn State’s Russell E. Larson Agricultural Research Center in central Pennsylvania, the researchers applied RhizoSorb once at the beginning of the three-year experiment at three different rates. Then they applied poultry litter at three different rates in each of the three years. Each year, they measured water-extractable phosphorus in the top three inches of soil. The research plots were managed as continuous corn production and used no-till practices.

They found that applications of poultry litter increased phosphorus levels in the soil. As more manure was applied, the amount of water-extractable phosphorus increased, and phosphorus built up more each year. RhizoSorb increased the amount of phosphorus that stayed in the soil between 26% and 53% in the first and second year of the study.

“These results are promising, but we only measured phosphorus in the soil, not in actual runoff water after rain,” White said. “So, we need to conduct more research to confirm that RhizoSorb actually reduces phosphorus loss in real field-runoff conditions. While the efficacy of a single application of RhizoSorb in reducing water-extractable phosphorus may last for as long as two years, future research could address whether additional applications in subsequent years could maintain this effect.”

That’s a prospect Phospholutions — the company that developed and markets RhizoSorb — welcomes, according to Steve Levitsky, chief administrative and sustainability officer for the company and a Penn State alumnus. He noted that the nearly 10-year-old company is presently concentrating on its core enterprise of expanding sales of RhizoSorb 8-39-0, a granular fertilizer that he called the next generation of phosphorus fertilizer.

“We have tested our product in 14 countries now and our vision is to replace the phosphorus fertilizers that are currently out there with our 8-39-0 product,” he said “Research like this helps show the many use cases for the technology and the downstream benefits it offers; we hope to explore more ways to bring the technology to market in the future, including in manure-application areas.”

Penn State helped Phospholutions by nurturing the startup through its Invent Penn State entrepreneurial ecosystem, providing foundational research, legal and financial support. Phospholutions was founded by College of Agricultural Sciences alumnus Hunter Swisher in 2016, and the Rhizosorb product is covered by multiple patents.

Jesen Hosch, first author on the study, was a research assistant in the Department of Plant Science. Co-author Zachary Sanders graduated with a doctoral degree in soil science and biogeochemistry. Contributing to the research from Phospholutions were Levitsky, Taylor Strehl and Pauline Welikhe.