Soybeans rose, heading for the longest rally since 2007, and corn climbed to a one-month high on speculation that hot, dry weather will reduce crop yields in the U.S., the world's leading exporter.

High temperatures will rise to as much as 12 degrees Fahrenheit above normal for seven days starting tomorrow in the Midwest, Mike Tannura, the president of T-storm Weather LLC, said in a telephone interview. As much as 46 percent of the corn crop and 44 percent of soybeans have drier-than-normal topsoil, and the adverse conditions may extend into August, he said.

"Hot, dry weather will rob yield potential," Don Roose, the president of U.S. Commodities Inc. in West Des Moines, Iowa, said in a telephone interview. "The crops are getting smaller, and we don't have any excess inventories to offset the losses."

Soybean futures for November delivery rose 11.5 cents, or 0.8 percent, to $13.955 a bushel at 10:27 a.m.. on the Chicago Board of Trade. The oilseed headed for the 10th straight gain, the longest rally since September 2007. Before today, the price climbed 44 percent in the past 12 months.

Corn futures for December delivery jumped 14.75 cents, or 2.2 percent, to $6.9325 a bushel. Earlier, the price reached $6.96, the highest for a most-active contract since June 14. Before today, the grain surged 71 percent in the past year.

Corn is the biggest U.S. crop, valued at $66.7 billion in 2010, followed by soybeans at $38.9 billion, government figures show.