Corn and soybeans rose on speculation that adverse weather will limit output in South America and lift overseas demand for U.S. supplies. Wheat gained, capping the longest rally in almost 11 months. Dry conditions the next 10 days will increase stress on crops in Argentina and southern Brazil, where most areas have had less than half the normal rainfall since Dec. 1, Mike Tannura, the president of T-Storm Weather LLC in Chicago, said in a telephone interview. Above-average temperatures beginning Dec. 27 will accelerate soil evaporation, Tannura said. “The forecasts point to the increasing threat for crop losses,� Jerry Gidel, a market analyst for North American Risk Management Services Inc., said by telephone from Chicago. “People are betting that yield losses in South America will increase U.S. exports.� Corn futures for March delivery rose 0.3 percent to close at $6.195 a bushel at 1:15 p.m. on the Chicago Board of Trade, capping the first six-session gain since December 2010. The grain advanced 6.3 percent this week, the biggest such increase since mid-October. Still, the price has fallen 1.5 percent this year on rising world grain production. Soybean futures for March delivery rose 0.1 percent to close at $11.725 a bushel, the seventh straight gain and the longest rally since July 15. The oilseed climbed 2.9 percent for the week, paring the annual loss to 16 percent. Top Exporters The U.S. was the world’s largest producer and exporter of both commodities in the marketing year that ended Sept. 30. The Department of Agriculture says Brazil will top the U.S. this year as the largest shipper of soybeans. Argentina is the second-biggest corn exporter after the U.S. The adverse weather in South America is similar to the 2008-2009 growing season, when a La Nina pattern strengthened in December, T-Storm’s Tannura said, leading to a 30 percent plunge in Argentina’s corn and soybean output, a 13 percent decline in Brazil’s corn production and a 5.3 percent drop in soybeans. This December has been even drier in Argentina than in 2008, Tannura said. China, the biggest consumer and buyer of soybeans, may import 6.1 million metric tons of the oilseed in December, the most in 18 months, the Ministry of Commerce said today on its website. “China may increase purchases� of U.S. corn and soybeans as South American crop risks increase, Don Roose, the president of U.S. Commodities Inc., said today. Wheat futures for March delivery rose less than 0.1 percent to $6.22 a bushel, after gaining 7.3 percent in the prior five sessions. The grain has fallen 22 percent this year on rising world production and slowing demand for U.S. supplies. Corn is the biggest U.S. crop, valued at $66.7 billion in 2010, followed by soybeans at $38.9 billion. Wheat was in fourth place, at $13 billion, behind hay, government data show. The CBOT will be closed Dec. 26 for the Christmas holiday. To contact the reporter on this story: Jeff Wilson in Chicago at jwilson29@bloomberg.net To contact the editor responsible for this story: Steve Stroth at sstroth@bloomberg.net

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