GRAINS-Soybeans retreat as demand worries overshadow USDA's production cut

By Karl Plume

CHICAGO, Aug 14 (Reuters) - U.S. soybean futures declined for the first time in four sessions in a profit-taking setback on Thursday after a rally ignited by the U.S. government's lower-than-expected harvest outlook took prices to six-week highs.

Concerns about soybean export demand due to trade tensions with top buyer China continued to hang over the market.

Corn futures drifted lower under continued pressure from the U.S. Department of Agriculture's bigger-than-expected harvest forecast earlier this week, although strong export demand limited losses.

Chicago Board of Trade wheat, meanwhile, dropped to fresh contract lows on ample global supplies.

Grains markets stumbled after this week's soybean-led advance, and traders are awaiting further production updates from private forecasters, including from a large corn and soybean crop tour scheduled to survey yield potential across seven states next week.

November soybeans SX25 were down 14-3/4 cents at $10.29-1/2 a bushel at 12:30 p.m. CDT (1730 GMT) earlier climbing to its highest point since July 3.

"We had a 60-cent rally from the lows in soybeans last week and that's probably about enough," said Jack Scoville, analyst with the Price Group.

"And even though we're going to have less supplies, I don't think anybody's of the opinion that the Chinese are going to be buying anything soon, so we still have to find homes for all those beans," he said.

U.S. soybean exporters risk missing out on billions of dollars worth of sales to China as trade talks between Washington and Beijing drag on, according to traders.

December corn futures CZ25 were down 1 cent at $3.96-1/4 a bushel as strong export demand blunted supply pressure from a likely record-large U.S. crop.

CBOT September wheat WU25 was down 4-1/4 cents at $5.03 a bushel after sliding, along with all other contract months, to a fresh lifetime low.