Here is the chart for corn since the ethanol blending madate went into effect.
LINK TO CHART
The 2005 energy bill mandated that 4 billion gallons of renewable fuel (mostly corn-based ethanol) must be added to the gasoline supply in 2006. That amount rises to 4.7 billion gallons for 2007 and 7.5 billion in 2012. These targets represent a large percentage increase in ethanol use but are still only a small fraction of the 140 billion gallons of gasoline that the U.S. currently uses every year.