There's a new tool to keep environmental phosphorus levels in check. The Iowa Phosphorus Index is a risk-management instrument that uses a number of factors to calculate potential phosphorus loss from a field. A team of Iowa State University researchers and Natural Resource and Conservation Service staff developed the P-Index.

Gerald Miller, associate dean of the Iowa State College of Agriculture and team coordinator, says the P-Index provides a loss rating, which can be useful in understanding the process of phosphorus delivery to surface water. Research shows that phosphorus runoff can cause algae blooms and other water quality problems.

The P-Index equation includes three components:

1. The erosion component is made up of five factors that help determine the potential amount of phosphorus delivered to surface water with sediment. These factors include conservation and other management practices.

2. The second component deals with potential phosphorus delivered to surface water in runoff. It takes into account precipitation levels, soil tests, recent phosphorus applications and the method and timing of those applications.

3. The third component considers the potential for phosphorus to move through sub-surface drainage. Precipitation, underground tiles, soil type and soil test phosphorus levels all impact this component.

Miller cautions that the index does have its limits. "The P-Index is a tool to be used by planners and land users to assess the risk that exists for phos-phorus moving off of agricultural fields toward a surface water body. It's inten-ded to be part of the NRCS nutrient management planning process that takes place between the land user and resource planner," he says.

In addition, Miller notes that this tool isn't an evaluation scale to deter-mine if you're within water quality or nutrient management standards established by government agencies.

USDA's state technical committee will make recommendations on any modifications to the P-Index before it is put into use in Iowa. Final phosphorus rules are due to the state NRCS conservationist by April 1, 2001. Once the state NRCS adopts the final rules, you will find an electronic version of the Iowa Phosphorus Index and user's guide at www.ia.nrcs.usda.gov.

For more information, contact Gerald Miller, at (515) 294-4333.

www.ia.nrcs.usda.gov