* Corn rebounds from contract lows on short-covering
* U.S. corn, soy crop prospects seen improving
* Wheat firms but CBOT December ends August down 13 pct
(Updates prices, adds quotes, changes byline, changes dateline from previous LONDON) CHICAGO, Aug 31 (Reuters) - U.S. corn prices rose about 3.5 percent on Thursday, snapping a four-session slide as grain traders joined a broad rally in commodities on the last day of the month. Soybeans and wheat followed the firm trend. Chicago Board of Trade December corn futures settled up 12-1/4 cents at $3.57-3/4 per bushel after dipping to $3.44-1/4, a contract low. CBOT November soybeans ended up 12 cents at $9.45-1/4 a bushel and CBOT December wheat finished up 4-3/4 cents at $4.34-1/2 a bushel. Corn posted the biggest percentage gain among the grains as traders took profits by exiting short, or sold, positions. "It just feels like anybody that was short probably covered and said, 'Let's make the month of August look good in the books,"' said Joe Lardy, analyst with CHS Hedging. The 19-market Thomson Reuters CoreCommodity CRB Index was up about 2.3 percent and hit its highest level since Aug. 10. Even with Thursday's rally, December corn ended August down 27 cents a bushel, or 7 percent. The market has been pressured recently by improving prospects for U.S. 2017 corn production, which mitigated worries about spring planting delays and patches of dryness in July. After the CBOT close, brokerage INTL FCStone raised its estimate of the U.S. 2017 corn yield to 166.9 bushels per acre (bpa), from 162.8 in its previous monthly report released Aug. 1. The firm raised its forecast of the U.S. 2017 soybean yield to 49.8 bpa, up from its Aug. 1 figure of 47.7. Strong corn export sales data lent support. The U.S. Department of Agriculture reported export sales of U.S. corn in the latest week at 992,500 tonnes (old and new crop years combined), above a range of trade expectations for 400,000 to 900,000 tonnes. CBOT soybeans rose, halting a four-session slide in the November contract. Like corn, November soybeans fell during August, sliding 62 cents per bushel or 6.2 percent. Wheat followed the pattern, with CBOT December ending modestly higher on Thursday on short-covering but posting a sharp monthly decline of roughly 13 percent. CBOT wheat rallied in June and early July, with the spot contract reaching a two-year high as drought gripped the northern U.S. Plains spring wheat belt. But futures have since fallen on reminders of ample global wheat stocks overall.
CBOT settlement prices:
Net Pct Volume
Last change change
CBOT wheat WZ7 434.50 4.75 1.1 77347 CBOT corn CZ7 357.75 12.25 3.5 265094 CBOT soybeans SX7 945.25 12.00 1.3 108045 CBOT soymeal SMZ7 299.50 2.10 0.7 39570 CBOT soyoil BOZ7 35.06 0.37 1.1 57354
NOTE: CBOT September wheat, December corn and November soybeans shown in cents per bushel, December soymeal in dollars per short ton and December soyoil in cents per lb.
(Additional reporting by Nigel Hunt in London and Colin Packham in Sydney; Editing by Subhranshu Sahu and Sandra Maler)