(Updates with closing prices, adds soybean sale)
By Mark Weinraub
CHICAGO, Sept 29 (Reuters) - U.S. soybean futures firmed on Thursday on a mild round of bargain buying and short-covering ahead of a key government report on Friday, traders said.
Signs of strong export demand for the oilseed also lent support to soybean futures but gains were kept in check by reports of good yields from fields in the western part of the U.S. Midwest as harvest ramped up.
Wheat futures fell on a technical setback amid ample global supplies. Corn futures ended unchanged as traders squared positions ahead of the U.S. Agriculture Department's closely watched quarterly stocks report on Friday.
"Nobody wants to really make a commitment one way or the other," said Bill Gentry, a broker at Risk Management Commodities in Lafayette, Indiana.
Chicago Board of Trade November soybean futures settled up 4-3/4 cents at $9.50-1/4 a bushel.
USDA on Thursday morning reported export sales of U.S. soybeans in the latest week at 1,692,900 tonnes, topping a range of trade expectations for 1.1 million to 1.3 million.
Additionally, USDA on Thursday morning said that exporters reported the sale of another 120,000 tonnes of soybeans to China for delivery in the 2016/17 marketing year. That followed announcements of other deals with the world's top buyer of the oilseed earlier this week.
"Soybeans are edging higher .... but it's hard to get any big rally in prices because of plentiful supplies," said Phin Ziebell, agribusiness economist at National Australia Bank.
CBOT December corn futures were unchanged at $3.29-1/4 a bushel.
USDA said export sales of corn totaled just 575,000 tonnes, below a range of trade expectations for 750,000 to 950,000 tonnes. The bearish figure hung over the corn market throughout the trading day.
CBOT December soft red winter wheat futures ended down 4-1/4 cents at $3.99 a bushel. The contract firmed during overnight trading but hit resistance as it neared its 30-day moving average, a level it has not traded above since Aug. 22.
Rains could continue slowing harvesting of corn and soybeans in the eastern Midwest up to the weekend, but the west of the crop belt looks dry until at least Tuesday, the Commodity Weather Group said in a daily note.
Additional reporting by Naveen Thukral in Singapore and Gus Trompiz in Paris; Editing by David Evans and Tom Brown