There’s less of a problem with sulfur than phosphorus (P) in Nebraska alfalfa fields, says Charles Shapiro, University of Nebraska soil scientist. Soils in other states are also suffering from a lack of P, according to a recent fertility report from the International Plant Nutrient Institute (IPNI).
Growers, Shapiro says, “need to keep their phosphorus levels up. Good alfalfa removes a lot more phosphorus than corn, and growers might not provide as much for alfalfa as they should.”
Compared to 2005 data, P levels have decreased by 6 parts per million (ppm) to a median 25 ppm, according to the IPNI report, called The Fertility of North American Soils, 2010. Less than 25 ppm indicates deficiency, according to most university recommendations.
The Corn Belt shows the most consistent P declines, dropping 6 ppm to a 2010 median level of 22. “This decline has major agronomic significance, since a high percentage of samples from this region now test below critical levels and call for annual P fertilization to avoid yield reductions,” the report indicates.
The northern Great Plains generally has the lowest P levels and the Northeast continues to have some of the highest soil P levels in the nation.