There was little interest in buying grain just a few days after Christmas and ahead of year-end holidays.
"If I left at 11:30 every day, no one would know I'm gone," said a wheat trader. "The phone doesn't ring. There's nothing going on."
Declines in barge freight combined with ample supplies and no fresh export sales pressured the CIF market, which supplies grain export terminals at the Gulf Coast.
Corn offers fell as much as 5 cents per bushel. Nearby soyabean offers fell about 2 cents per bushel, also pressured by a drop in CIF values.
South America remained the cheapest source of soyabeans, despite harvesting its crop about 10 months ago.
Traders said China paid 45 cents per bushel premium to the CBOT March on a free-on-board basis in recent days for one cargo of Argentine soyabeans for January-February shipment.
FOB offers for US soya for the same delivery period were quoted at 52 cents over at the time the business was done, traders said. FOB offers are now quoted at 50 cents premium.
Barge freight bids and offers eased slightly on the Mississippi River at St. Louis and on the Illinois River. On the lower Ohio River, barges traded at 400 to 415 percent of tariff, unchanged from Tuesday, a barge operator said.
Nearby soft red winter wheat offers were steady, supported by slow farmer selling.
Hard red winter wheat dropped about 2 cents per bushel amid farmers bringing fresh supplies to the market and a lack of export demand. "You've got some farmer selling and no one buying on the other side," said the wheat trader.
Exports were quiet except for the Commodity Credit Corp (CCC) announcing it will tender on Tuesday to buy 32,600 tonnes of sorghum for South Africa for January delivery.