(Updated with further details from the government's 2011 crop forecast.)

NEW YORK (

TheStreet

) -- The boom in crop prices will motivate the nation's farmers to plant more acres of corn and wheat this year than experts were anticipating, the USDA said in its annual planting forecast Thursday.

The news would normally put pressure on ag commodities prices -- and agricultural shares tend to trade in line with commodities.

But the USDA also released crop-inventory data alongside its planting forecast, and grain stocks continue to be so low that a bigger-than-expected harvest in 2011 wouldn't affect the supply-demand picture enough to undermine the trends that have lifted food prices since last year, agricultural pros say.

According to the USDA, corn inventories in the U.S. have declined by 15% from a year ago. Stocks now stand at 6.5 billion bushels, a little more than half of it stored in silos on farms.

Likewise, soybean inventories decreased, though not as severely, falling 2% from last March. Wheat stocks, however, grew by 5% from a year ago.

In late-morning trading on the Chicago Mercantile Exchange Thursday, the May corn futures contract was approaching $7 a bushel, adding 30 cents.

On the equities markets, meanwhile, shares of fertilizer producers were mostly higher.

Potash

(POT)

was rising by about 1% to $58.66,

CF Industries

(CF) - Get Report

was gaining more than 4% to $137.97, and

Agrium

(AGU)

was adding 2% to $91.50.

Farm-equipment maker

Deere

(DE) - Get Report

saw its shares rise 2% to $96.41.

Shares of

Mosaic

(MOS) - Get Report

, which reported results that appeared to underwhelm investors after the closing bell Wednesday, were in the red, shedding 1% to $79.63 at around noon on Thursday.

The USDA said it expects U.S. farmers to plant 92.2 million acres of corn, slightly more than 91.7 million acres that the conventional wisdom in the market had been targeting, according to the trade web site

Agriculture.com

. That's up 5% from a year ago and would represent the second-largest planted acreage in the U.S. since 1944. In 2007, farmers planted 93.5 million acres.

Wheat acres are expected to come in at 58 million, higher than the 41.2 million expected by market participants.

The soybeans forecast, however, was slightly below expectations. The USDA believes farmers will plant 76.6 million acres, while the market was predicting about 77 million, according to Agriculture.com.

-- Written by Scott Eden in New York

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