CHICAGO, Sept 24 (Reuters) - U.S. corn and soybean futures dropped to their lowest in more than a week on Thursday, with investors locking in gains made from a recent rally as combines rolled across key production areas of the Midwest, traders said.

"The grains appear to be in full-on profit-taking mode this week as the 2020 harvest ramps up, with yield reports particularly for soybeans) undeniably producing phrases like 'better than expected' or 'producer pleased', despite dryness in much of the heart of the Corn Belt this summer," Matt Zeller, director of market information at StoneX, said in a note.

A flurry of export sales to China, together with concern over weather damage to U.S. crops, had fanned a rally in Chicago prices.

Wheat futures ticked higher after sagging 3.8% so far this week, with speculators covering short positions as the U.S. dollar consolidated around a two-month high. The currency rally, which makes dollar-denominated commodities like wheat more expensive to overseas buyers, had depressed prices.

Traders shrugged off a weekly U.S. Agriculture Department report that showed export sales of corn at 2.139 million tonnes and export sales of soybeans at 3.195 million tonnes. Both topped the high end of market expectations.

But the USDA did not report a fresh deal for soybeans to China in its daily reporting system, snapping a stretch of 14 straight trading days a so-called flash sale has been announced.

"Beans were down all day, off harvest pressure, lack of Chinese buying overnight," Charlie Sernatinger, global head of grain futures at ED&F Man Capital said in a note.

CBOT November soybean futures dropped 14-1/2 cents to $10.00 a bushel and CBOT December corn ended down 5 cents at $3.63-1/2. Both contracts hit their lowest since Sept. 16.

CBOT December soft red winter wheat gained 3/4 cent to $5.49-3/4. (Additional reporting by Naveen Thukral in Singapore and Gus Trompiz in Paris; Editing by Mark Potter, Jonathan Oatis and Cynthia Osterman)