SYDNEY  - U.S. corn futures edged up on Monday, extending gains into a fourth session as strong Chinese demand and concerns about North American production pushed prices towards a three-week high.

Soybean prices inched higher, while wheat firmed.

The most active corn futures on the Chicago Board of Trade were up 0.3 percent at $3.79-1/4 a bushel by 0202 GMT, having gained 0.5 percent in the previous session when prices marked their highest since Feb. 8 at $3.80-3/4 a bushel.

"The U.S. Midwest remains too wet for planting in some regions. That delay still has the potential to mean that less corn might be planted overall," said Tobin Gorey, director of agricultural strategy, Commonwealth Bank of Australia.

A farmer survey by crop advisory firm Farm Futures on Friday said U.S. growers will plant 1.9 percent more corn acres this year and 3.7 percent less soybeans.

The U.S. Department of Agriculture announced corn sales totalling 300,000 tonnes to China on Friday - the largest purchase by Beijing in five years.

The orders came following weeks of rumours that Beijing was poised to make a goodwill purchase of the grain amid ongoing U.S.-China trade talks.

The most active soybean futures Sv1 were up 0.2 percent at $9.05-1/2 a bushel, after ending down 0.6 percent on Friday.

The most active wheat futures were up 0.2 percent at $4.66-3/4 a bushel, having closed down 0.1 percent on Friday when they earlier touched their highest since Feb. 27 at $4.74 a bushel.

The USDA is due to release its annual planting prospects report next Friday.

(Reporting by Colin Packham; Editing by Joseph Radford)

(( colin.packham@thomsonreuters.com ; +61-2 9321 8161; Reuters Messaging: colin.packham.thomsonreuters.com@reuters.net ))

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