Barge freight rates for this week were sharply lower on the Illinois, lower Mississippi and lower Ohio rivers.
Freight bids fell 75 percent of tariff on the lower Mississippi River at St. Louis and on the Illinois River. Bids fell 50 percent of tariff on the lower Ohio River.
Traders said freight rates were under pressure from a lack of demand as the Midwest harvest drew to a close.
The lower freight weighed by corn basis values in the CIF market, with November bids slipping 3-5 cents a bushel.
"Barge freight is falling, and there is some corn moving," a river trader said.
Traders said FOB corn basis offers were steady, supported by export demand. Traders said there was interest from Mexico, Venezuela and Egypt.
Soft red winter wheat basis offers were higher, in line with gains in the CIF market, traders said, adding that farmers were holding out for higher prices.
"There's a big 'carry' in the market and nobody's selling anything," a trader said, referring to higher prices for deferred sales.
Hard red winter wheat basis offers were lower, weighed by declines in the track market fuelled by lower rail freight.
Another day passed without USDA confirmation of the sale of 1 million tonnes of US wheat to Iraq. A senior Iraqi trade official said last week that Iraq bought the wheat from two US companies for arrival from December.