The corn basis also fell by 13 cents at Savanna, Illinois, on the Mississippi River, reflecting a softer tone in corn bids at the US Gulf export terminal.

However, the corn basis firmed at an ethanol plant in Union City, Illinois.

Corn bids in the eastern half of the Midwest have been unusually strong in recent weeks as processors struggle to pry old-crop corn from farmers concerned about how much new-crop corn they will be able to produce.

Soybean basis bids were mostly steady to firm on Monday, supported by a thin pace of farmer selling.

The exception to the trend was Savanna, Illinois, where the soybean basis weakened by 7 cents.