March corn fell 14.25 cents, or 2 percent, to settle at $7.3725 a bushel.
Soybeans also fell. The January contract lost 19 cents, or 1 percent, to end at $14.7225 a bushel.
Sterling Smith, futures specialist at Citi in Chicago, said there was continuing fallout on corn prices from the very weak export report issued by the Department of Agriculture Thursday.
Very dry conditions have also led to low water levels and restrictions on the amount of cargo that can be carried on barges on the Mississippi. Traders worry that U.S. corn is already facing tough competition from low-priced grain from South America.
"There's a continuing hangover from yesterday's export report," Smith said. "Today, there wasn't really anyone looking to buy."
In other commodities trading, copper rebounded following a drop the day before when the European Central Bank cut its forecast for growth in the euro region for next year.
Copper for March delivery rose 1.85 cents to $3.6630 a pound.
Other metals futures also rose. Gold for February delivery rose $3.70 to $1,705.50 an ounce. March silver rose 1.70 cents to $33.131 an ounce and January platinum rose $6.30 to $1,607 an ounce. March palladium rose 95 cents to $698 an ounce.
In energy trading, benchmark oil dropped 33 cents to finish at $85.93 per barrel on the New York Mercantile Exchange.
Heating oil fell 2.79 cents to finish at $2.9153 per gallon; wholesale gasoline rose less than a penny to end at $2.5974 per gallon and natural gas fell 11.5 cents to finish at $3.551 per 1,000 cubic feet.