Ohio’s Changing Phosphorus Risk Index

Farmers are caretakers of the land. While growing crops from the soil, they monitor its health and add nutrients as needed. In turn, they have been held increasingly responsible for the water that passes over and through their fields and what that water carries with it as it goes.

According to researchers at Ohio State’s College of Food, Agricultural, and Environmental Sciences, phosphorus tops the list as the nutrient most often implicated in the degradation of surface water and contributions to algal blooms. While agriculture is not the only source of phosphorus, the industry recognizes the need to take action and be part of a solution, including an industry collaborative project called “On-Field Ohio!”

“Phosphorus is increasingly being used to judge farmer performance, so we have to get it right. Farmers are willing to make changes, but the recommendations need to be based on science,” said Dr. Elizabeth Dayton, a soil scientist at Ohio State and principal investigator for the On-Field Ohio! project, which is part of the University’s larger Field to Faucet initiative.

Dayton is working on the data and scientific basis needed to rewrite the Ohio Phosphorus (P) Index that is intended to provide a field-scale estimate of P runoff risk based on characteristics (such as degree of slope or soil type) and crop management practices (current P levels, fertilizer applied, application method and tillage).

Research efforts are focused on areas where the farmer has some control, looking more at the concentration than the total volume in the runoff events of more than 29 surface and/or tile drainage monitoring sites. Sites are located across farms in Ohio’s current priority watersheds – the Scioto, Grand Lake St. Mary’s and Western Lake Erie Basin.

Runoff events are classified as either baseline events, associated with year round runoff activity, or spike events, associated with short-term high-risk events, for example, major rainstorms, tillage, or surface fertilizer application.

Presently the project has more than 2,000 recorded run-off events that have generated more than 14,000 water samples with more than 42,000 water analyses. In addition, the project has collected 2,000 soil samples and performed 8,000 soil analyses. The data will continue to accumulate as the study progresses.

“The edge-of-field studies were always intended to be long term, but we’re hoping to summarize where we are to suggest a preliminary revision for the P Index, this year” said Dayton.

The P Index also utilizes the Tri-State Fertility Guidelines – currently being studied for revision by Dr. Steve Culman also at Ohio State which would be considered in the P Index results.  Current data suggests huge benefits come from banding or injecting fertilizer instead of surface application, but keeping P levels within the Tri-state recommendations also keeps dissolved P concentrations low. Particulate bound P can be reduced by reducing tillage and maintaining field surface.

On-Field Ohio! is supported in part by Ohio farmers through the Ohio Soybean Council (OSC), Ohio Corn Marketing Program, Ohio Small Grains Marketing Program, Ohio Farm Bureau Federation and many other agricultural partners.

“Water quality is important for our state; we depend on these resources for recreation, tourism, jobs and a healthy ecosystem. Farmers want to be part of the change that puts us closer to a solution and this study is a key component of that journey,” said Terry McClure, OSC Chairman and soybean farmer from Paulding County.