Managing Soils For Phosphorus

Phosphorus is one of the three nutrients usually added to soil as fertilizer. One of the main roles of phosphorus is energy transfer in plants. Adequate levels stimulate early plant growth and hastens maturity. If there’s not enough, it could affect yield.

Daniel Kaiser is an Extension nutrient management specialist at the University of Minnesota. He says the best way to know how much phosphorus is available in the soil, is to do a soil test.

"Most of the soil tests that are out there are indexes of response and they don’t measure the total amount of phosphorus that’s out there because our soils contain large quantities of phosphorus, but only very small amounts typically are available to plants," he says. "So, with a soil test, we’re trying to use it more as an index tool, or a risk assessment tool, to try to determine whether or not the soil can supply enough phosphorus for a particular crop we’re growing within a given year."

Phosphorus is very chemically reactive to other elements in the soil such as iron, aluminum, and calcium. This can change the nutrient’s availability, and affect how it’s managed in some soils.

"There isn’t one-size-fits-all management strategy just because of some of these reactions that are taking place," says Kaiser. "Particularly with soils in the Midwest, we know that some soils have a large amount of calcium. That can tend to react with the phosphorus, and can render it unavailable for a period of time."

Let soil phosphorus levels, crop, and soil characteristics guide your decisions on fertilizer and manure rates, timing, and methods of application.

Learn more about managing phosphorus in the soil