Corn futures in Chicago plunged to the lowest levels in more than three months after the government reported higher than expected acreage and stockpiles, indicating easing pressure on tight grain supplies and relief for livestock producers squeezed by soaring feed costs.

The nation’s farmers sowed 92.28 million acres to corn this year, up 4.6 percent from 2010 plantings and the second-highest total in the past 67 years, the U.S. Department of Agriculture said in its Acreage report June 30.

Grain traders and analysts were caught by surprise by the plantings figure, which exceeded expectations by about 1.5 million acres, based on a Dow Jones Newswires survey. CME Group corn futures fell the daily 30-cent trading limit in some contracts and may have further to drop, meaning a record rally since the beginning of 2010 is probably finished, some analysts said.

“The party is over for the corn bulls,” Chad Henderson, an analyst with Prime-Ag Consultants, Inc., in Brookfield, Wis., said in a June 30 e-mail.

In trading June 30, corn futures for July delivery fell 69 cents, or nearly 10 percent, to $6.29 a bushel, after sinking as low as $6.15 ¼, the lowest price for a closest-to-expiration contract since $6.08 in mid-March. The 69-cent decline was the second-largest one-day price drop in the history of the corn futures contract, next to a drop of $1.31 ½ in July 1996, according to Garrett Toay of in Clive, Ia. The front-month contract trades with no price limits.

December corn futures, which reflect expectations for this fall’s harvest, fell 30 cents, the maximum initial daily move allowed by the exchange, to $6.20 ½, a decline of 14 percent from a contract-high settlement of $7.14 June 9.

Corn futures are down 20 percent from a June 10 settlement of $7.87, an all-time closing high for a front-month contract, but still up 78 percent from $3.54 ¼ a year ago.

The December contract “could have difficulty holding a $6 handle,” Mike Zuzolo, president of Global Commodity Analytics & Consulting LLC, said in a report.

Estimated corn plantings for 2011 would trail only the 93.53 million acres seeded in 2007 as the highest since 1944, according to the USDA report. In a separate June 30 report, the USDA said nationwide corn stockpiles at the beginning of this month totaled 3.67 billion bushels, down 15 percent from a year earlier but higher than analysts’ expectations by about 350 million bushels.

Hedge funds, Wall Street banks and other speculators recently cut bullish bets on corn prices after buying heavily over the past year. The USDA reports will likely prompt speculators to further reduce “long” positions, which profit when prices rise, analysts said.

Speculators holding longs “will endure further pain with no help from weather,” Rich Feltes, vice president of research with R.J. O’Brien & Associates, said in a report. He expects longer-term corn futures to decline to the $5.50 to $5.75 area.

“Things are looking up for ethanol plants and livestock producers,” Feltes said.

Planting got off to a slow start this spring because of wet conditions across much of the Midwest, and was at a “virtual standstill” during mid-April due to heavy rains and lowland flooding in the central and eastern Corn Belt, the USDA said. But drier weather in late-May and June allowed many farmers to catch up on fieldwork, and barring a severe drought or any other widespread weather problems this summer, the nation’s farmers may be headed toward a record corn harvest, based on USDA estimates.

Farmers are expected to harvest 84.9 million acres, the USDA said June 30. Based on a previous USDA estimate for an average U.S. yield of 158.7 bushels an acre, this year’s acreage would generate a crop of about 13.47 billion bushels, up 8.2 percent from last year and above the current record of 13.09 billion bushels in 2009.

U.S. corn stockpiles by the end of the 2010-11 marketing year Aug. 31 are expected to shrink to 730 million bushels, a 15-year low, according to a previous USDA forecast. With this year’s higher acreage, supplies next year may surpass 1 billion bushels, said Dave Kurzawski, an analyst with INTL FCStone, LLC, in Chicago.

“This is a very bearish report on corn,” Kurzawski said.

For soybeans, this year’s plantings will total an estimated 75.21 million acres, the USDA said. That’s down 2.8 percent from the 77.4 million acres seeded 2010 and about 1.27 million acres below analysts’ expectations.

In trading June 30, July soybean futures fell 28 cents to $13.06 ¼ a bushel, while November futures fell 29 cents to $12.94.