GRAINS-Corn extends slide as trade woes, big S.American crops spur selloff

Recasts; updates prices, adds quotes, changes byline, changes dateline from previous HAMBURG

By Julie Ingwersen

CHICAGO, March 3 (Reuters) - Benchmark U.S. corn futures fell on Monday for a sixth straight session, sliding nearly 3% as worries about trade tensions and ample South American harvests appeared to spur commodity funds to liquidate more of their large net long position, traders said.

Soybean and wheat futures turned lower as corn futures sagged.

As of 12:59 p.m. CST (1859 GMT), Chicago Board of Trade corn Cv1 was down 12-1/2 cents at $4.57 per bushel after hitting $4.54-1/2, the lowest on a continuous chart since January 9. CBOT soybeans Sv1 were down 12-3/4 cents at $10.13 a bushel and wheat Wv1 was down 8 cents at $5.47-3/4 a bushel.

The most-active contracts for all three grains hit their lowest levels since mid-January.

U.S. President Donald Trump is expected to decide what levels of tariffs he will impose early on Tuesday on Canada and Mexico amid last-minute negotiations over border security and the flow of fentanyl.

Meanwhile, China has American agricultural exports in its cross hairs as it prepares countermeasures against fresh U.S. import tariffs, China's state-backed Global Times reported.

Late in the CBOT trading session, Trump alerted America's farmers to coming U.S. tariffs on "external product," telling them to get ready to sell their goods domestically.

China is a major importer of U.S. soybeans and Mexico is a key corn buyer, while wheat could also be hit by retaliation against any U.S. tariffs.

In Brazil, farmers are roughly halfway through the harvest of what is projected as a record-large soybean crop.

"(South American) supplies are set to overwhelm the global marketplace regardless of any localized crop concerns, and the trade is reflecting that export issue right now. Lingering tariff talk just adds more fuel to that fire," StoneX senior market analyst Matt Zeller wrote in a client note.

Commodity funds hold a hefty net long position in CBOT corn futures, leaving that market particularly vulnerable to bouts of long liquidation.

Traders shrugged off news that the U.S. Department of Agriculture confirmed private sales of 114,000 metric tons of U.S. corn to Mexico.