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Declining crop yields
There are many reasons for high commodity prices. But recent data from FAO shows a pretty rapid slowdown in productivity growth. The price spike in 2008 occurred in a particularly bad year in which yields declined on a worldwide basis for three of the four largest food commodities. In 2009 all four of the majors saw yield declines, something that hasn't happened since 1974. 2010 couldn't have been much better and was probably worse, given how bad things were in the U.S, the world's largest producer and exporter (worldwide data for 2010 isn't available yet).
More at link.
Probably, there are several reasons but, obviously, Monsanto is not going to feed the world.