Biofuels opponents amplified calls Friday to the Obama administration to end a national corn ethanol requirement following the release of disappointing crop yield estimates.

Agriculture Department predictions for corn supplies came in lower than expected in its biannual review. The 123.4 bushels per acre yield projected Friday is the lowest since 1995, and the anticipated 10.78 billion bushel haul would be the lowest since 2006.

The drought has given environmentalists and ranchers an opportunity to criticize the renewable fuel standard (RFS) beyond their standard talking points. That rule requires refiners to blend 13.2 billion gallons of corn ethanol into traditional fuel this year.