Agricultural soil phosphorus levels held steady or trended downward in at least 80 percent of Ohio counties from 1993 through 2015, according to recent findings from the College of Food, Agricultural, and Environmental Sciences at The Ohio State University.

The findings, part of the college’s Field to Faucet initiative, represent good news for Ohioans concerned about protecting surface water quality while maintaining agricultural production, according to college researchers Elizabeth Dayton, Steve Culman and Anthony Fulford.

“Soil phosphorus levels are strongly related to runoff water phosphorus levels. Less phosphorus in the soil should result in reduced phosphorus runoff risk,” Dayton said. “These findings show that Ohio farmers are doing a good job of managing soil phosphorus levels.

“While there is still room for improvement where soil phosphorus levels are higher than crop needs, the fact that so many counties show soil phosphorus levels trending down indicates Ohio farmers are moving in the right direction."

Phosphorus soil testing is an important tool farmers use to determine if phosphorus fertilizer is needed for crop growth, and if so, how much. In Ohio, crop-specific phosphorus fertilizer recommendations come from the Tri-State Fertility Guidelines.

“Farmers are being asked to avoid applying phosphorus fertilizer beyond crop needs,” Culman said. “Maintaining soil phosphorus levels within the appropriate agronomic range minimizes phosphorus runoff risk, while providing sufficient crop nutrition.”

For this study, data for more than 2 million phosphorus soil tests from 1993 to 2015 were provided through the cooperation of the three biggest soil-testing laboratories serving Ohio agriculture: A&L Great Lakes of Fort Wayne, Ind.; Brookside Laboratories of New Bremen, Ohio; and Spectrum Analytic of Washington Court House, Ohio.

In 2015, the median soil phosphorus level was within the appropriate agronomic range in 87 of 88 Ohio counties, assuming nutrition needs for a typical Ohio crop rotation. 

“The next step will be to compare trends in county-level phosphorus fertilizer sales and crop yield data with the soil phosphorus information,” Fulford said.