Nope, that's the cover story. The US subsidizes production, not capacity, which results in lots of excess crop that gets dumped on the market and depresses prices and impoverishes competitors. The ethanol mandates were created partly as a response to the problems that this created. But they are mandates for blending in a certain amount of ethanol, producing artificial demand, and putting us in the ridiculous situation where 40% of corn production goes to ethanol that nobody needs. It's the dumbest thing ever and makes no sense, but is very popular with farm states for obvious reasons.

If we actually wanted to maintain spare production capacity, it would look very different. We'd have to pay to keep land capable of growing food even when not growing any. We'd subsidize the inputs (irrigation, drainage, soil) instead of the outputs. We'd avoid overproduction instead of encouraging it, since it's a form of "inflation" that lowers prices and drives out farmers (other than the ones printing money... er, growing unneeded corn).