While steel tariffs are currently grabbing most ag headlines these days, possible changes to the Renewable Fuel Standard (RFS) may produce longer term challenges for U.S. agriculture. Battle lines between oil refiners and ethanol producers and their suppliers (corn growers) have been clearly drawn.

In large part, ethanol has literally fueled much of the growth U.S. agriculture has experienced in the past dozen years because corn is the principal feedstock in producing the fuel additive…