Michael Pollan's excellent Omnivore's Dilemma, ISBN-13 978-1594200823, features an anecdote about the Mayans early on in the first chapter. The Maya word that referred to themselves and their civilization was "corn walker," and often you hear Chicanos and other Mexican indigenous peoples using that term on themselves even today. But Pollan points out that in fact North Americans are truly corn, walking. The reason we know this is because corn is particularly greedy when it comes fixing carbon, especially carbon-13, from the atmosphere, which leaves a nice carbon trail throughout the food chain; to wit, our carbon-13 to carbon ratios in body mass often exceed persons with corn visibly more abundant in their diets (eg, the bulk of the average Mexican's diet consists of tortillas, tamales, things fried in corn batter, drinks made with corn, etc). But a more thorough look at the diet of a typical American reveals a food landscape overwhelmed with corn: high fructose corn syrup, corn emulsifiers, modified food starches, corn-based vitamin supplements (some which even enrich bleached white flour!) and perhaps most insidiously, livestock feed. And everywhere corn is, so goes carbon-13.
One resource that corn uses in abundance to fix carbon-13 and create carbohydrates and some proteins is nitrogen, which was found in the soil abundantly only 100 years ago. Since corn taxes the nitrate levels of soil, traditional multi-purpose farming would rotate in crops capable of fixing nitrogen from the atmosphere. Carbon is abundant and easyc to fix from gas, nitrogen is not easy to fix from the atmosphere and is therefore more scarce than carbon in terms of its availability to plants. One such crop that would rotate in after corn is a legume such as soybeans or peanuts, which lives in symbiosis with bacteria which fix nitrogen in exchange for glucose on the plant's roots. And for centuries, corn and legumes would rotate, one consuming the soil's supply of nitrogen and the other replenishing, year after year. This changed in last century when in 1909 a German Jew named Fritz Haber figured out an industrial process for fixing nitrogen to create ammonium nitrate, the industrial fertilizer used today to feed millions of acres of hungry corn stalks (as well as blow up federal buildings). He used his know-how in World War I to create a vast array of nitrate for explosive manufacture, as well as developing poison gases. He developed Zyklon B, which was ironically used to gas Jews during the Holocaust.
The downside of industrial nitrate fixing is that it requires a great deal of energy to do, energy that comes from burning coal or oil. A conservative estimate is that for each calorie of corn created, three calories of fossil fuels is burned -- but the true cost may be as much as 6-10 to one calorie where a farmer over-fertilizes, in transportation and processing cost, etc, or even more. All for something which growths naturally with neutral or even negative carbon impact on the environment. Consider the disparity of pounds of feed to pounds of meat in raising beef, and you begin to see the negative impact of industrial corn and meat cultivation in the United states: it takes roughly 32 pounds of corn to produce 4 pounds of weight gain in cattle (an 8:1 ratio), as opposed to a 2:1 ratio in chicken. Work backwards from a single calorie of grain-fed beef and you're burning maybe 100 calories of fossil fuels.
All of this, *ALMOST* makes me want to become a vegetarian. And then, gordonzola lights up my Friends Page with something like this: Suzanne Sommers, poet, and I want to eat a steak.
Excerpted in salon.com: http://www.salon.com/books/awards/2006/12/14/pollan_excerpt/index.html
Reviewed in salon.com (includes interview with author): http://www.salon.com/books/int/2006/04/08/pollan/index.html