CHICAGO - U.S. soybean futures fell to a one-week low on Friday and recorded a second straight weekly decline, pressured by fresh cancellations of U.S. soybean sales, traders said.

Corn futures fell for a fourth straight session and also notched a weekly drop, while wheat futures firmed after a three-session slide.

Chicago Board of Trade November soybean futures settled down 6-3/4 cents at $8.56-3/4 per bushel. CBOT December corn ended down 3-3/4 cents at $3.67 a bushel. December wheat rose 1-3/4 cents at $5.14-3/4 a bushel.

Soybeans turned lower, retreating from early gains, after the U.S. Department of Agriculture said private exporters cancelled sales of 180,000 tonnes of U.S. soybeans to China, the world's biggest buyer.

The USDA said exporters also cancelled another 120,000 tonnes of optional-origin soybeans sold to unknown destinations.   

The soybean market has been roiled by the Sino-U.S. trade conflict, with Chinese buyers steering clear of beans from the United States, instead increasing purchases from Brazil and reducing their use of the bean in animal feed.

"We really are struggling with exports, and to have cancellations on top of an already slow export pace, evidenced by our weekly export sales yesterday, it's really another negative blow for the bulls," said Brian Hoops, analyst with Midwest Market Solutions.

The USDA's weekly U.S. export sales figures for both soybeans and corn, released Thursday, fell well below trade expectations.

Corn futures fell following a pick-up in U.S. harvest activity and farmer selling this week. However, some unexpected rains stalled fieldwork in the northwestern Midwest, Hoops said.

"Some rain showed up overnight in parts of Iowa and Minnesota. This is on top of very wet conditions," Hoops said. 

"We are behind the normal pace of harvest, and next Monday we are going to be way behind."

The soybean harvest in No. 2 producer Iowa was only 19 percent complete by Oct. 14, the slowest for this time of year in USDA records dating to 1981.

CBOT wheat futures ended modestly higher in a technical bounce after the December contract notched a one-week low at $5.10-3/4 a bushel. However, for the week, the contract fell about 0.5 percent.

CBOT November soybeans declined of 1.2 percent and CBOT December corn fell 1.8 percent.        

(Additional reporting by Nigel Hunt in London and Naveen Thukral in Singapore; editing by David Evans and Tom Brown)

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