Des Moines Register: President Barack Obama’s speech at Newton on Wednesday was especially noteworthy for its lack of reference to ethanol. It was one of the rare times in recent history that a president or national politician has spoken in Iowa and didn’t mention the biofuel by name, especially as Iowa leads the nation in ethanol production. Iowa has 41 ethanol plants up and running or under construction, but ethanol producers have struggled of late with declining corn prices and drops in the price of …