CHICAGO, Jan 4 (Reuters) - U.S. soybean futures extended a rally to fresh 6-1/2 year highs on Monday as dry crop weather and disruptions to exports in South America continued to unsettle investors at a time of brisk Chinese demand, analysts said.

But corn and wheat futures were choppy, paring gains after both commodities surged to six-year highs.

As of 1:06 p.m. CST (1906 GMT), Chicago Board of Trade March soybeans were up 4 cents at $13.15 per bushel after surging to $13.49-1/2, the highest price for a most-active soybean contract on a continuous chart since June 2014.

CBOT benchmark corn was down 1 cent at $4.83 a bushel after hitting $4.97-3/4, nearing the $5 mark for the first time since May 2014. CBOT March wheat was up 1 cent at $6.41-1/2 a bushel.

Life-of-contract highs were set in nearly all CBOT soybean, corn and wheat futures months.

Grain markets pared gains and turned lower at times as Wall Street equities sagged, investors booked profits and U.S. farmers seized the moment to sell some of their last harvest and portions of the 2021 crop as well.

"It's been a long time since we've seen new-crop (prices) this high, especially on beans," said Dan Cekander, president of DC Analysis.

Uncertainty about soy and corn supplies in Argentina and Brazil continued to support the market, sending futures sharply higher in early moves.

"New year, same old issues," Commerzbank said in a note.

"As 2021 begins, it is once again the same concerns about limited supply from South America and strong Chinese demand that are driving up soybean and corn prices."

Argentina's announcement last week of a suspension of corn exports until March, to ensure ample domestic food supply, deepened uncertainty about South American crops as dry weather continued to raise doubts over upcoming harvests.

The news came just after a near three-week strike by Argentina oilseed crushing workers that disrupted supply from the world's largest exporter of soymeal livestock feed.

Grain markets have been sensitive to any risks over South American supply as strong Chinese import demand has already absorbed much available soy and corn on the world market.

These factors helped corn, soybean and wheat futures notch up double-digit percentage gains over 2020.

(Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Bernadette Baum and David Evans)