Updating Ohio’s Phosphorus Risk Index is generating positive initial results

Maintaining agricultural soil phosphorus levels in accordance with the Tri-State Fertility Guidelines helps lower the concentration of phosphorus that is dissolved in agricultural runoff, according to ongoing research by a CFAES soil scientist.

And because erosion matters, phosphorus associated with eroded sediment can be curtailed by reducing soil disturbances such as tillage and by maintaining field cover either as crop residue or a growing crop, says Elizabeth (Libby) Dayton, a scientist in the college’s School of Environment and Natural Resources.

Her On-Field Ohio project seeks to update and revise the Ohio Phosphorus Risk Index, which is a U.S. Department of Agriculture-Natural Resources Conservation Service tool used by farmers to assess their risk of phosphorus moving off farm fields. The index is an integral part of a nutrient management plan, Dayton said, that is intended to provide farmers a field-scale estimate of their phosphorus runoff risk. She talks about the project in the video above.

Phosphorus is the agricultural nutrient most often implicated in the degradation of Ohio surface water and contributes to harmful algal blooms.

“Our intention is to keep the focus on things a farmer can control,” she said. “To that end, the project evaluates, among other practices, erosion potential, the amount of phosphorus in the soil, planned fertilizer, and/or manure application amounts and methods.

“We are quantifying how differences in practices result in meaningful differences in phosphorus runoff risk, thus providing guidance for management decisions. These and other examples demonstrate that meaningful reductions in phosphorus runoff can be achieved without harming Ohio agricultural production.”

The project includes runoff monitoring on 29 farm fields in the Scioto, Grand Lake St. Marys and Western Lake Erie Basin watersheds. To date, the project has collected data on more than 2,000 runoff events and more than 14,000 runoff water samples, resulting in more than 42,000 analyses. It has also collected 2,000 soil samples, resulting in more than 8,000 analyses.

“Using statistical analyses, runoff events can be separated into spike or short-term high-risk events associated with a major rainstorm, erosion due to a major soil disturbance or fertilizer application,” Dayton said. “Also evaluated are baseline or chronic year-round phosphorus runoff risks associated with erosion and soil phosphorus levels.”

In addition to keeping residue cover on fields to lessen erosion risk, other initial findings of the project show that practices such as banding or injecting fertilizer or manure application substantially reduce phosphorus runoff risk, she said.

The project’s next steps include summarizing all the data to date with a goal to release a preliminary revised version of the index later this year, Dayton said. An updated Ohio Phosphorus Risk Index can play an important role in agricultural phosphorus management, she said.

“Balancing between protecting Ohio surface water quality while maintaining agricultural production is a charge we take seriously,” Dayton said. “I am increasingly optimistic that it can be done.”

Support for the project comes from a USDA Natural Resources Conservation Service Conservation Innovation Grant and from Ohio farmers through the Ohio Soybean Council and Ohio Corn and Wheat. The project is part of the college’s Field to Faucet initiative.

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