Swanson started out by planting 20 percent of his acreage with Roundup Ready soybeans, which are spliced with a gene developed by biotechnology giant Monsanto to make them resistant to the company's popular and biodegradable Roundup Ready herbicide.

Like the quiet revolution in Swanson's fields, genetically modified (GMO) soybeans have won the hearts of most U.S. farmers and account for 63 percent of the oilseed grown this year.

But just as eagerly as he embraced Roundup Ready soybeans, Swanson turned his back on gene-modified corn this year for the same basic reason: it saved him no money.

Most gene-altered corn is modified with a bacterium from the soil to make the crop deadly to the European corn borer, an insect that in some years has caused farmers millions of dollars in damage. "We haven't had much of a problem with the pest. Not enough to justify planting GMO corn," Swanson said.

"Roundup Ready soybeans have been economical and benefit the environment because there is no run-off in Roundup herbicide," he said in a telephone interview.

Swanson said savings from using Roundup herbicide ranged from $5 to $10 an acre, working out to about $2,250 in average savings for an American farmer with 300 acres (121 hectares) of soybeans. That is significant savings for a farmer, who will earn only about $47,000 for his 300 acres of soybeans at current prices.

Such savings for cash-strapped farmers - less fuel, less tillage, less herbicide - remain the driving force behind the success of GMO soybeans.

Preliminary results of a study done this year by the National Center on Food and Agricultural Policy of 30 crops conclude that Roundup Ready soybeans cut grower costs by an average of $15 an acre (0.447 hectare), representing savings of $735 million for 49 million acres.

Insect-resistant cotton was estimated to have earned farmers an extra $99 million from an extra 260 million pounds (117.9 million kg) of cotton from the GMO acreage, which also cut pesticide use by 2.7 million pounds (1.225 million kg) annually.

WARY EYE ON EUROPE, CHINA

But the flip side of the cost benefits for farmers has been disrupted demand for GMO crops, especially for corn and soybeans, the use of which spreads out all over the food chain from animal feeds to cooking oils.

In Europe, consumer groups have been ferocious opponents of gene-altered crops, destroying test plots and demanding research to guarantee that GMOs will not harm humans, animals or the environment.

European consumers, worried after a decade of mad cow disease and more recently foot-and-mouth, have been wary, leading European food makers and retailers to demand "non-GMO" ingredients from suppliers.

The result is that a farmer in Illinois harvesting GMO soybeans this month will usually earn 5 cents to 10 cents a bushel less than a farmer with non-GMO beans.

Top processor Archer Daniels Midland, which ships huge amounts of grain products to Europe, is offering up to 20 cents more per bushel for non-GMO soybeans this month at its giant Decatur, Illinois, processing complex.

The European Union has proposed strict labeling and traceability rules for GMOs - rules that the United States says are unworkable, unrealistic and unreasonable.

U.S. Agriculture Secretary Ann Veneman has said that if no compromise was found, a World Trade Organization complaint was an option. The United States and Europe have already fought to a WTO stalemate over the EU's refusal to allow imports of U.S. beef produced with a genetically altered bovine growth hormone.

China, another huge U.S. market for soybean exports, jolted traders in June by announcing vague new rules that require labeling and certification of GMO products.