GRAINS-Corn futures higher on export demand, short-covering

* Soy futures sag on big U.S. harvest but still gain for week

* Drier Midwest weekend seen after rains this week

(Updates with closing U.S. prices) CHICAGO, Sept 21 (Reuters) - U.S. corn futures climbed more than 1 percent on Friday to their highest in more than a week, buoyed by end-user demand and fund short-covering, analysts said. Wheat and soybean futures declined but still recorded weekly advances. Chicago Board of Trade December corn settled up 4-3/4 cents at $3.57-1/4 per bushel after reaching $3.57-3/4, its highest since Sept. 12. CBOT November soybeans ended down 3 cents at $8.47-1/4 per bushel and December wheat fell 2-1/4 cents at $5.21-3/4 a bushel. Corn rose for a third straight session after hitting a contract low at $3.42-1/2 on Tuesday, with analysts citing a mix of technical and fundamental factors. Commodity funds hold a sizable net short position in CBOT corn, leaving the market vulnerable to bouts of short covering. After the close, weekly Commodity Futures Trading Commission data showed funds in the week to Sept. 18 had expanded their net short position to the widest since late January. Meanwhile, export demand has been strong. The U.S. Department of Agriculture said private exporters sold 121,700 tonnes of U.S. corn to unknown destinations in the past day, and U.S. export sales data released Thursday showed weekly corn sales exceeded market estimates at 1.4 million tonnes.

"Coming into today, we were still the cheapest corn in the world. End-users want to get covered at these prices," said Don Roose, president of Iowa-based U.S. Commodities. Some analysts are uncertain about the USDA's forecast this month of a record-high average corn yield of 181.3 bushels per acre, given early anecdotal harvest reports. "It looks like a record bean crop is still there. The corn yields are a little more variable," Roose said. Rains slowed the corn and soy harvest in the northwestern Midwest this week, although the weekend should be mostly dry. Soybean futures fell as traders returned their focus to the massive U.S. crop and the ongoing trade dispute with China, the world's top soy buyer. The United States does not have a scheduled date to announce for another round of talks with China, a senior White House official said. Still, the November soybean contract posted a weekly rise of about 2 percent, clawing back from a contract low set Tuesday at $8.12-1/4. Similarly, CBOT December wheat declined on Friday but rose about 2 percent for the week. Traders appeared to shrug off news that Russia's IKAR consultancy lowered its estimate of Russia's 2018 wheat crop to 69.2 million tonnes, from 69.6 million previously. Russia is the world's biggest wheat exporter.

CBOT settlement prices:

Net Pct Volume

Last change change

CBOT wheat WZ8 521.75 -2.25 -0.4 41310 CBOT corn CZ8 357.25 4.75 1.3 145744 CBOT soybeans SX8 847.25 -3.00 -0.4 78996 CBOT soymeal SMZ8 308.90 -5.50 -1.7 46502 CBOT soyoil BOZ8 28.34 0.48 1.7 77566

NOTE: CBOT December wheat and 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 Gus Trompiz in Paris and Naveen Thukral in Singapore; editing by Tom Brown and Diane Craft)