I'm certainly not in favor of ethanol subsidies or mandates, but most of the land I see being diverted to corn and other agronomic field crops is from hayland and cropland coming out of CRP. This is in response to the relatively high price of corn, soybeans, etc. in recent years.
Here's a breakdown of (field) corn supply and utilization for the 2010/11 marketing year in million bushels(
http://www.usda.gov/oce/commodity/wasde/latest.pdf) and
http://www.ers.usda.gov/media/815354/fds12f.pdf)
Supply:14,182
Utilization:
feed & residual -- 4,793
food, seed, industrial (FSI) -- 6,428*
exports -- 1,834
Ending Stocks -- 1,128
* The FSI uses are
HFCS -- 521
glucose and dextrose -- 272
starch -- 258
alcohol for fuel --5,021**
alcohol for beverages -- 135
cereals -- 197
** This use has byproducts for animal and human use: distillers' grains, corn gluten feed and meal, and corn oil.
BTW, the acreage devoted to sweet corn is miniscule relative to field corn, 269K
http://usda01.library.cornell.edu/usda/current/VegeSumm/VegeSumm-01-26-2012.pdf versus 99.6 million in 2010.
Steve