Farmers in the Corn Belt are not applying enough phosphorous to replenish the amounts being removed by their primary crops, according to a new, nationwide summary of soil test levels.

The summary, compiled by scientists with the International Plant Nutrition Institute, shows that soil test levels for phosphorus in the region have seen a decline of 6 parts per million since the last survey was conducted in 2005.

“This decline has major agronomic significance since a high percentage of samples from the region now test below critical levels and call for annual phosphorus fertilization to avoid yield reductions,” the authors of the study said.

The 6-ppm-decline mirrors the drop in soil test values for phosphorus on the North American continent, they wrote in a recent article in the IPNI’s “Better Crops with Plant Food,” magazine. The survey results come from comparisons of 4.4 million soil samples taken from throughout North America.

For an article summarizing the results of the study and instructions on how to order a copy, go to http://www.ipni.net/ipniweb/portal.nsf/0/c13f0cf310f1903e062577c7005a4bd7/$FILE/Fertility%20NA%20Soils%202010.pdf.