CFAES Give Today

School of Environment and Natural Resources


Revised Phosphorus Index Can Help Curb Agricultural Runoff

March 1, 2018
Photo: Thinkstock

This news article originally appeared on the website of the College of Food, Agricultural, and Environmental Sciences and was written by Tracy Turner.

COLUMBUS, Ohio – Ohio farmers will soon have access to a newly revised tool that can quickly and easily tell them their risk of agricultural phosphorus runoff that could potentially move into Ohio waterways such as Lake Erie.

All with the help of an online program.

The revised Ohio Phosphorus Risk Index is a program developed by the U.S. Department of Agriculture’s Natural Resource Conservation Service to help farmers assess their risk of phosphorus moving off farm fields. It will soon allow farmers to input their farm-specific data to generate their risk of phosphorus in agricultural runoff.

The revised index is the result of the multiyear On-Field Ohio project led by Elizabeth (Libby) Dayton, a researcher in the College of Food, Agricultural, and Environmental Sciences (CFAES) at The Ohio State University.

The index has significant water quality implications statewide, considering that misapplied phosphorus has a high likelihood of degradation Ohio’s surface water and is a major contributor to harmful algal blooms, experts say.

The revised phosphorus risk index can help Ohio farmers better work toward meeting the 40 percent phosphorus reduction target in the Western Lake Erie Basin, said Dayton, a soil scientist in the college’s School of Environment and Natural Resources. That is the target agreed to in the 2012 Great Lakes Water Quality Agreement between the United States and Canada.

Scientists believe that a reduction of this size would keep algal blooms at safe levels for people and the lake.

“The index provides a long-term, average estimate of field-scale phosphorus loss based on farmer specific inputs,” Dayton said. “It gives farmers the ability to compare crop management scenarios and evaluate changes in phosphorus runoff, allowing them to prioritize time and resources when making management decisions.

“The index quantifies how voluntary changes in agricultural practices contribute to achieving target phosphorus runoff reduction goals. If you multiply that by the millions of crop acres in Ohio, the 40 percent reduction target appears achievable.”

The need to reduce phosphorus is significant because harmful algal blooms are dangerous to both the Lake Erie ecosystem and human health. In 2014, for instance, toxins produced by a severe bloom in western Lake Erie shut down Toledo’s drinking water supply for two days.

The On-Field Ohio project included runoff monitoring on 29 farm fields in the Scioto River, Grand Lake St. Marys and Western Lake Erie Basin watersheds. The project 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 also collected 2,000 soil samples, resulting in more than 8,000 analyses.

Some of the management practices that were evaluated included tillage, soil type, fertilizer placement, soil phosphorus content, field topography, soil infiltration rate and cover crops.

In addition to revising the Phosphorus Risk Index, Dayton’s project found that 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.

And because erosion contributes to the issue, phosphorus associated with eroded soil can be curtailed by reducing soil disturbances with practices such as reduced tillage and by maintaining crop residue or a growing crop on the field at all times.

“By inputting different crop management scenarios into the index, farmers can determine what will work best to reduce their soil disturbance,” Dayton said. “Reductions in soil disturbance translate into large reductions in soil erosion and surface runoff of phosphorus that is attached to eroded soil, which is the biggest risk driver for surface phosphorus runoff in Ohio.”

The On-Field Ohio project was funded through a $1 million USDA Conservation Innovation Grant and $1 million in matching donations from Ohio farmer groups.



Tracy Turner


Elizabeth Dayton