SIOUX CITY, Iowa — The world needs more corn, and U.S. farmers will do everything they can to meet the demand.

"That's just the nature of the American farmer," said John Scott, who runs a farming operation with his brother near Odebolt in Iowa. "We will give the market what it wants."

But to produce more corn, needed to feed livestock and the booming ethanol industry, the nation also must create more nitrogen fertilizer. Such fertilizer is used to treat about 96 percent of corn planted in the United States to ensure high yields.

That increased demand has pushed manufacturers to crank out fertilizer at near capacity and has pushed up profits for many companies. Manufacturers have seen stock prices more than double since last summer.

Charlie Rentschler, an analyst with New York-based Wall Street Access, said improved profits and higher trading prices for fertilizer companies are driven mostly by the immense popularity of planting corn. Higher corn prices are expected to drive farmers to plant millions of additional acres this spring.

"Farmers are going to pile into producing corn this spring," Rentschler said. "The reason why corn prices are up is initially because of ethanol. That's been a tremendous consumer of corn."

Corn is a huge consumer of nitrogen fertilizer.

"Certainly we're very positive about the fact that growers today have a very good income opportunity in grain production," said Michael Bennett, president and CEO of Terra Industries Inc. The Sioux City-based company operates six plants and makes anhydrous ammonia, the basic ingredient for most nitrogen fertilizers; urea ammonium nitrate, known as UAN, a liquid fertilizer widely used in North America; and ammonium nitrate and urea, both nitrogen-based fertilizers.

Terra's stock hit all-time highs in recent weeks, up to $18.93 earlier this month. Shares had been trading at below $6 a share as recently as last June.

Other companies also are seeing strong performance: