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Keeping P in its Place

Keeping P in its Place

Applying nutrients at the right source, rate, time and place

The potential for nutrients to move from farm fields to waterways is under scrutiny by the American public, as well as by federal and state regulators. However, Gary Tuxhorn, Ph.D. and principal scientist for United Suppliers in Ames, Iowa, says that environmental consciousness among farmers remains high and is increasing, particularly where phosphorus (P) is concerned.

"Phosphorus runoff is a significant concern for everyone," says Gary Tuxhorn, Ph.D. and principal scientist for United Suppliers in Ames, Iowa, "especially in highly-sensitive watershed areas such as the Chesapeake Bay, the Great Lakes and the Gulf of Mexico. Phosphorus has much lower water solubility than nitrogen, and under some conditions and in some geographic areas, phosphorus can be more soluble and subject to runoff.

As a rule, P moves through the soil very slowly – only centimeters per year. Fortunately, there are a number of environmental measures that can reduce phosphorus runoff, increase fertilizer use efficiency and contribute to higher yields. 

These measures include reducing and limiting soil erosion, as well as properly managing rates of applied P to ensure the best possible conversion of bushels of grain per pound of P applied. Use of cover crops, Variable Rate Technology (VRT), injection of P under the soil surface and planting of grass filter strips where water leaves a field are also effective measures to reduce P runoff, according to Tuxhorn.

Another situation that makes P management tricky: between 75 and 95 percent of the applied nutrient often gets tied up or “fixed” in the soil during the year following application due to a chemical process that makes the P unavailable for plant uptake.

"This chemical process is due to the interplay of positive and negative charges between the phosphorus and elements such as calcium, magnesium, aluminum and iron," Tuxhorn explains. "When this happens, the phosphorus is unavailable for plant uptake, remaining instead in the soil and subject to off-site movement or erosion."

That’s the very thing that our friends over at The Fertilizer Institute are focused on – environmental protection through science-based approaches and the 4R’s of nutrient stewardship. By applying at the right source, rate, time and place, farmers can improve both the environment and their bottom line.

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