CHICAGO – Farmers will plant the most acres in a generation this year, led by the biggest corn crop since World War II, taking advantage of the highest agricultural prices in at least four decades.

They will sow corn, soybeans and wheat on 226.9 million acres, the most since 1984, a Bloomberg survey of 36 farmers, bankers and analysts showed. The 2.5 percent gain means an expansion the size of New Jersey, as growers target fields left fallow last year and land freed up from conservation programs.

Crop prices, some of which reached the highest averages ever in 2011, bolstered the economies of Midwest growing states, sent net farm income up 28 percent to $100.9 billion and pushed the value of farmland to a record $2,350 an acre, the U.S. Department of Agriculture estimates. Global food costs are down 11 percent from a peak a year ago as grain output rises from China to Canada, U.N. data show.

“There is unlikely to be any ground that won’t be planted this year,” said Todd Wachtel, a 40-year-old who farms about 5,700 acres in Altamont, Ill., and plans to expand his corn fields by 21 percent when seeding begins in early April. “Farmers know that they have to plant more when prices are high because they may not last.”

A bigger harvest in the United States, the world’s largest exporter of all three crops, will help compensate for shortages in the current crop year.

Farmers will sow corn, used to feed livestock and make ethanol, on 94.329 million acres this year, up 2.6 percent from last year and the most since 1944, according to the Bloomberg survey.

Soybean fields may expand 0.4 percent to 75.309 million acres, the fifth-most ever. Both crops are harvested after the current season ends on Aug. 31.

Wheat in the season that begins June 1 will reach a three-year high of 57.233 million acres, up 5.2 percent, the survey showed.

Corn may rise 7.1 percent to $6.90 a bushel in six months because of the damage in South America, before dropping to $5.25 in a year as U.S. farmers increase supply, Goldman Sachs said in a Feb. 2 report.

Wheat may tumble 18 percent to $5.50 by July and soybeans may drop 17 percent to $10.20 a bushel, analysts at commodity broker Allendale Inc. in McHenry, Ill., said Jan. 21.

“The area is available to have huge crops this year,” said Paul Meyers, a vice president at Foresight Commodities Services Inc. in Long Valley, N.J., and the former head of grain-market analysis at the U.S. Department of Agriculture from 1974 to 1983. “We are headed for a surplus-supply situation.”

Corn, soybean and wheat futures are down at least 15 percent since the end of August, helping to send the Standard & Poor’s GSCI Agriculture Index to a 16 percent decline.

The MSCI All-Country World Index of equities gained 4.7 percent during the period, touching a six-month high Feb. 3, while Treasurys returned 2.5 percent, a Bank of America Corp. index shows.

World food prices fell to a 14-month low in December, led by declines in grains, sugar and oilseeds, the U.N.’s Food and Agriculture Organization said Jan. 12.

The USDA affirmed its forecast for moderating food costs last month. Prices will increase 2.5 percent to 3.5 percent in 2012, below last year’s 3.7 percent gain, the agency said Jan. 25. The same day, the International Monetary Fund forecast a 14 percent drop in non-oil commodities this year, citing more supply.

Farmers in the Midwest, the main growing region, are less than two months away from planting seeds, and dry soils in some areas could limit output.

The most widely held option on December corn futures gives the holder the right to buy the grain at $7.

“It’s been an abnormally warm winter,” said Alan Tiemann, who is preparing to expand corn planting on his 2,000-acre farm in Seward, Neb., by 15 percent. “That may not relate to what’s going to happen this summer, but it keeps you on the edge of your seat a little bit, wondering when the next moisture event is going to happen.”