HAMBURG - Chicago wheat was weakened on Monday by expectations the safe shipping channel to export grain from war-torn Ukraine will be extended.

Slow demand weighed on soybeans and corn, which fell ahead of world supply and demand estimates on Wednesday from the U.S. Department of Agriculture (USDA).

Chicago Board of Trade most-active wheat was down 1.4% at $6.98-1/2 a bushel at 1214 GMT. Soybeans fell 0.4% to $15.11-3/4 a bushel, and corn fell 0.5% to $6.36-1/4 a bushel.

Turkey’s foreign minister said Ankara is working hard to extend the safe shipping agreement that enables Ukraine to export grain, which expires in mid-March.

"Wheat is being undermined today by intensifying market expectations that Ukraine’s safe shipping agreement will be extended this month," said Matt Ammermann, StoneX commodity risk manager.

"The Turkish government said it is working to get the agreement extended while over the weekend there were not major negative comments from Russia about the deal."

"An extension would keep Ukrainian grain flowing into world markets at a time when Russian wheat is also being offered cheaply."

Worries drought would cut Argentina’s harvests have recently supported soybean and corn.

"Corn is seeing weakness from the fall in wheat, with Ukraine a large corn exporter," Ammermann said. "Expectations of increased U.S. corn plantings are also in focus."

"Lack of demand, especially from China, is undermining both corn and soybeans today ahead of the USDA report on Wednesday."

Traders were positioning ahead of the USDA report, with the department expected to cut its forecasts of Argentina’s soybean and corn harvests and retain estimates of hefty Brazilian crops.

"The weather in Argentina remains bad but the huge size of the Brazilian soybean crop is also a bearish factor on the market," he said. "More possible U.S. interest rate rises could also hit demand."

(Reporting by Michael Hogan in Hamburg; Additional reporting by Naveen Thukral in Singapore; Editing by Jan Harvey)