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Yet more P needed in Corn Belt? New IPNI report.

April 12, 2011
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A new report from the International Plant Nutrition Institute (IPNI) indicates that median soil P levels in North America have declined quite a bit from 2005 to 2010 (by about 20%, from ~31 ppm to ~26 ppm).  Here’s a link to a new article about the report (http://tinyurl.com/6duzw2d) and the report itself (http://tinyurl.com/3pc6v6v).  Regional differences were notable and declines were particularly strong in corn-growing regions of the upper Midwest (Illinois, Minnesota, Michigan).  Interestingly, states along the Eastern seaboard (Virginia, New Jersey, Pennsylvania, New York, Connecticut) seemed to show significant net accumulation of soil P.  The authors include Dr Phil Mikkelson, who participated in the recent Sustainable Phosphorus Summit at Tempe.

The study is impressive, as it involves a summary of data from 4.4 million (!) soil samples.  Also included are data on other elements, such as Zn, K, and S.

Decline in soil P values from 2001 (blue) to 2005 (red) to 2010 (green). The decline is most consistent in the frequency of high soil P values.

What’s interesting here, of course, is that large quantities of P are already “locked up” in unavailable forms in agricultural soils, a legacy of past accumulations of fertilizer phosphorus.  Continuous application of more P is needed to provide a relatively small portion of fresh, “temporary” P that crop plants can grab.  This report indicates that corn farmers must, if they wish to avoid yield declines, keep adding and adding more and more to support sufficient corn production, as corn is one of the most P intensive of crops.  If fertilizer prices begin to rise and farmers cut back accordingly, it seems that they will have little “slack” left in soil P reserves to buffer themselves against yield decline.  Not good news for the bottom line and not good news for food production.

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