CORN IS EVERYWHERE. At the recent ag fair in Tulare, I was shown a government brochure that described all the different uses for corn: Swine food. Adhesives. Industrial wax. Herbicides. Read a label for any processed food, and you'll see corn lurking everywhere, disguised as "corn syrup" or "lecithin." Although operations like Monsanto strive to increase productivity—higher-yielding corn on bigger plots of land—we are not in need of more corn at the moment. According to some commodities brokers I spoke to, last year's "carry-over" of surplus corn was 2.1 billion bushels! (Each bushel weighs 56 pounds.) People may be starving elsewhere, but in America, granaries are brim full. In fact, there are so many corn products on the market precisely because of this excess—someone had to invent all those other uses for the surplus.

And then a Super Bowl ad came along and told us to go yellow—specifically, General Motors and its "Live green, go yellow" campaign. "Going Yellow" means using ethanol, a corn-based fuel additive that can be blended in some gas engines at an 85 percent blend. It's been around for a while, but now money-strapped GM is betting the, er, farm on it. The company has built 1.5 million flex-fuel cars and trucks already and seems ready to build more, if it can increase demand.

The ads have a feel-good quality. Forget irony or wit—this comes from the heart, GM wants us to know. The ad called "Maize" features questions asked by a lone person standing in a cornfield. "What if the answer to our dependence on oil was growing right in front of us?" for example. The choice of subjects—"young, multiethnic"—speaks to GM's bid for the hip audience. "Volunteers" shows young adults running around Manhattan passing out yellow T-shirts until everyone has one on. It's a growing trend!

On GM's website, the video "corncast" shows more interviews. They are supposed to feel improvised, as if these people weren't actors. The brilliant thing about the concept is that no GM executive has to make any statements of fact; the ads just let the people speak. One guy—"I like corn on the cob—popcorn!" reminded me of Forrest Gump. "At one point, a woman talks while a Toyota Prius is parked behind her. I can't believe that the ad makers didn't do this intentionally, sending some subliminal message about Earth-friendliness. If not, then what a goof. Then the people seem shocked that they can run corn in their engines. "I can never imagine a car running on a corn-based gasoline," Gump says, followed by a cool guy apparently asked the same question: "No problem with me."

Here's a problem. One-third of greenhouse gases are caused by agriculture. One-fifth of fossil fuel is used to grow and ship food. "When we eat corn, we're eating petroleum," Michael Pollan, a food writer, recently said. The petroleum-based fertilizers that are poured on the greedy corn, the pesticides sprayed on the crop, the combines and the tractors, and finally the semitrucks—all use or are derived from petroleum products.

The other problem with corn is its efficiency. According to the Worldwatch Institute, corn is fifth on the list for productivity—after sugar beets, sugarcane, cassava and sweet sorghum. Ethanol from corn yields only 1.5 units of energy for each energy unit used. The other bummer is a flex-fuel engine loses efficiency when running ethanol, so fuel mileage goes down.

Still, I know we need solutions. We are addicted to oil—even President Bush dared admit that for half a second before getting bitch-slapped by the Saudis. I would hope that a more efficient crop could be used, but in the meantime, we do have piles and piles of corn. So maybe we should use it.

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