Corn plunged the most allowed by the Chicago Board of Trade, and wheat and soybeans fell, after the government said U.S. stockpiles will be bigger than analysts expected, easing concern about tight supplies of food and fuel.

Corn inventories before next year’s harvest may climb to 900 million bushels, from a 15-year low of 730 million this year, the Department of Agriculture said today. The price as much as doubled in the past year, helping to send world food prices to a record in February, and boosting costs for livestock producers including Tyson Foods Inc. and JBS SA, and makers of ethanol including Archer Daniels Midland Co.

Exports of corn by the U.S., the largest grower, may drop to 1.8 billion bushels in the marketing year that begins Sept. 1, the lowest in nine years, the USDA said. The agency also lowered its estimate for shipments this year, reflecting slowing world demand as prices rise, said Jason Britt, the president of brokerage Central States Commodities Inc. in Kansas City, Missouri.

“At higher prices, you will eventually ration demand, and the market does its job,” Britt said. “We’re still historically tight, so you have to put everything in reference.”

Corn futures for July delivery tumbled 28.5 cents, or 4 percent, to $6.7875 a bushel at 10:09 a.m. on the CBOT. Earlier, the price dropped the 30-cent limit to $6.7725, the lowest since March 31. Before today, the grain rose 91 percent in the past year on record usage by ethanol producers and increasing demand from livestock farmers.

Wheat, Soybeans

Wheat futures for July delivery fell 27 cents, or 3.4 percent, to $7.7175 a bushel in Chicago. Before today, the most- active contract was up 62 percent in the past year, as drought slashed output in Russia while floods eroded supplies from Canada and Australia.

Domestic wheat stockpiles may total 702 million bushels next year, more than the 683 million expected by analysts, the USDA said. That’s still 16 percent less than projected inventories at the end of this marketing year on May 31.

Soybean futures for July delivery fell 15.25 cents, or 1.1 percent, to $13.2275 a bushel on the CBOT. Before today, the price rose 39 percent in the past year on record Chinese purchases of the oilseed, used to make livestock feed and cooking oil.

Corn is the biggest U.S. crop, valued at $66.7 billion in 2010, followed by soybeans at $38.9 billion, government figures show. Wheat ranked fourth at $13 billion, behind hay.