Farmers Can Be Optimistic, But Doubling in 5 Years?

From Chris Clayton's post on House Ag hearings:

Rep. Stephanie Herseth-Sandlin, D-S.D., also highlighted that technology is expected to continue boosting farmer yields for corn dramatically in the next five years. Secretary of Agriculture Tom Vilsack reiterated this perhaps a dozen times in his testimony. So if technology is going to allow corn yields to soar, perhaps come close to doubling, then why do we need an arbitrary 15-billion cap on corn-based ethanol in the Renewable Fuels Standard?

Of course, I may be misunderstanding this. But if corn yields are at 150 bushels or more, it's taken about 35 years for them to go from 100 to 150.

I know I'm old and have my head in a dark place (as Tom von G used to say) but when I hear of corn being used for ethanol I've just the beginnings of the same qualms I have when I hear of good farmland growing houses. Corn is for food. Yes, I know better, but that's my upbringing.