Chicago corn fell to its lowest in around four years on Monday and soybeans also dropped after a closely watched crop tour of key growing areas forecast bumper U.S. harvests.

Wheat fell amid ample world supplies, especially from the Black Sea region.

"The U.S. crop tour has estimated some big yields," said a Singapore-based grains trader. "It is the continuation of the same theme for beans and corn in Chicago futures today. Everything is pointing to a big production out of the U.S."

Chicago Board of Trade most-active corn fell 1.2% to $3.86-1/4 a bushel at 0958 GMT, its lowest since October, 2020.

Soybeans fell 0.8% to $9.64-3/4 a bushel, wheat fell 0.5% to $5.25-1/4 a bushel.

The U.S. soybean harvest will be even bigger than the government's record forecast, advisory service Pro Farmer said on Friday. The estimate came after a crop tour studying U.S. harvest conditions, though it forecast a smaller corn crop than the U.S. Department of Agriculture.

Pro Farmer forecast a U.S. soybean harvest of 4.740 billion bushels, or about 6% above the 2021 record and above the 4.589 billion bushels forecast by the agriculture department.

Farmers continue to sell old-crop corn and soy to make room for the harvest and to generate cash flow, traders said.

"For wheat, Black Sea export countries are dominating international sales at low prices, especially from Russia," one German trader said.

"Russian wheat export volumes also look like increasing sharply in the final days of August.

"Meanwhile, wheat demand is thin with hardly any international tenders in the market."

Fears of strike disruption to Canadian grain exports receded after the Canada Industrial Relations Board on Saturday ordered a halt to work stoppages at the country's largest railways.

(Reporting by Naveen Thukral in Singapore and Michael Hogan in Hamburg; Editing by Subhranshu Sahu, Eileen Soreng and Ed Osmond)