(Updates headline, byline; updates closing prices)
CHICAGO, Jan 6 (Reuters) - U.S. soybean and corn futures climbed to fresh 6-1/2 year highs on Wednesday, as worries about dry weather hurting Argentine crops attracted speculative buyers, analysts said.
Wheat futures fell on a lack of fresh supportive news and an upturn in the dollar, which tends to make U.S. grains less competitive globally.
Chicago Board of Trade March soybeans closed 14-1/2 cents higher at $13.61-1/2 per bushel after earlier reaching$13.78-1/4, the highest price on a continuous chart of the most-active contract since June 2014.
CBOT March corn added 3-1/4 cents to $4.95 per bushel after reaching $5.02-3/4 in mid-session trading, the highest benchmark corn price since May 2014.
March wheat slipped 6-1/2 cents to $6.47-1/2 per bushel.
Dry weather continues to threaten soy and corn yield prospects in Argentina, and labor issues in the South American country have added to concerns about supplies.
“A water deficit persists mainly in Argentina, leading to fears of a downward revision of corn production,” consultancy Agritel said.
The union representing Argentine port-side grain inspectors was to meet on Wednesday with agro-export companies to try to clinch a wage deal to end a strike that started on Dec. 9.
Underscoring recent volatility in the grain markets, the CME Group, parent of the CBOT, said it would raise the margins to trade its soybean, corn and wheat futures after Wednesday’s close.
“We have shaken some shorts out of the market with the CME increasing their (margins) ... If we continue to see a rally in this market, margins could potentially go up again,” said Terry Reilly, senior analyst with Futures International.
Meanwhile, traders have begun adjusting their positions ahead of the U.S. Department of Agriculture’s next monthly supply/demand report on Jan. 12, in which the government will release updated estimates of U.S. and South American crop production and usage. (Reporting by Christopher Walljasper; Additional reporting by Julie Ingwersen in Chicago, Gus Trompiz in Paris and Colin Packham in Sydney; Editing by Lisa Shumaker)