On-Field Ohio: Rewriting Ohio’s Phosphorus Risk Index to Keep Nutrients and Water on Fields

Elizabeth Dayton

COLUMBUS, Ohio – All farm field test sites have been selected and soil samples from fall testing dates have been collected as part of an ongoing three-year project by an Ohio State University College of Food, Agricultural, and Environmental Sciences researcher to revise an agricultural tool used by farmers statewide to better predict phosphorus runoff, offer them more management options and improve Ohio water quality.

The On-Field Ohio project, now in its second year, seeks to revise the U.S. Department of Agriculture-Natural Resources Conservation Service Ohio Phosphorus Risk Index to be more useful in predicting the risk of phosphorus moving off farm fields, said Elizabeth Dayton, a soil scientist in the college’s School of Environment and Natural Resources, who is conducting the project.

Dayton garnered a $1 million USDA Conservation Innovation Grant and $1 million in matching donations from Ohio farmers groups to complete the project.

Phosphorus is the agricultural pollutant often implicated in the degradation of Ohio fresh surface water and is a major contributor to harmful algal blooms, experts say.

Dayton’s goal is to make the P Index, used by farmers as part of nutrient management plans, more accurate and increase management options to reduce phosphorus runoff. She’s also working to create a Web-based tool so farmers can easily calculate and manage their offsite phosphorus transport risk, she said.

Some management practices being evaluated include tillage, soil type, fertilizer placement, soil phosphorus content, field topography, soil infiltration rate, drainage control structures and cover crops. 

To date, monitoring equipment has been installed on 30 farm fields in the Scioto, Grand Lake St. Marys and Western Lake Erie Basin watersheds, the latter two being the most problematic watersheds, she said.

Data is being collected on the soils, the farmers’ management practices, and surface and subsurface water runoff at the sites. The team has collected and analyzed more than 5,000 water samples thus far, Dayton said.

“This project would not be possible without the assistance of our participating farmers,” she said. “I cannot acknowledge often enough how much we appreciate their willingness to share their management information with us and allowing for the ongoing data collection.”

Key points:

  • Phosphorus is the agricultural pollutant often implicated in the degradation of Ohio fresh surface water and is a major contributor to harmful algal blooms.
  • Increased risk of phosphorus transport into surface water is associated with excessive and/or poorly managed phosphorus applications. 
  • Agricultural phosphorus runoff into Ohio waters harms the state’s economy in terms of fishing, recreation and drinking water sources.
  • Reducing agricultural nutrient runoff in Ohio should be beneficial to farmers by reducing input costs while protecting water quality.
  • The Ohio P Index is an integral part of nutrient management plans for both manure and commercial fertilizer application.
  • Ohio State research focuses on Grand Lake St. Marys and the Western Lake Erie Basin, which are the two most problematic watersheds in heavy agricultural areas.


Tracy Turner
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Elizabeth Dayton