Corn is the pillar of our food chain. Not in the same sense as, say, Mexicans who get the majority of their carbs directly from corn-based foods such as tortillas. No, our methods are far more indirect.
What we refer to as "corn" is actually maize, a cereal whose survival is symbiotically as dependent on us as we are on it.
Interestingly, the corn plant is capable of absorbing all carbon isotopes - even the heavier ones that most plants can't. This means that we can run samples of food through a mass spectrometer to determine what percentage originated as corn. The simple answer is lots.
That's because corn is the main feed for our industrial-scale dairy cows, our hens, and our livestock. It's also the raw material for a plethora of derivatives such as: corn starch, corn syrup (sucrose/ fructose used in colas and most other sweets), dextrose - a thickener, corn oil, vegetable oil, margarine, shortening, xanthan gum, and multodextrin. Try finding a processed food that doesn't contain at least one of those... I dare you. And don't forget that a huge amount of corn gets fermented into Ethanol for our cars.
Why do we rely on corn so much?
A good guess would be that it's highly efficient at converting sunlight into energy. It's pretty efficient at making carbs and sugars, but when you factor in all the extra energy that goes into farming, shipping, and processing corn... not really.
Then there's the argument that it's simple economics: corn is so cheap that it's profitable to use over other crops. Indeed, corn is cheap but that's because US farmers sell it at losses, sustained by their government.
Next argument: It makes great feed for livestock. It's known as an excellent "finisher" (ie: fed to them in their last weeks) for cows, causing a nice marbling of proteins and fats. But cows, and most other livestock, didn't evolve eating corn and have a difficult time with it; So much so that it is the greatest source of malady among industrial cows.
The author provides a starkly juxtaposing system, Management-Intensive Grazing, that is more productive/ efficient than modern farming, doesn't rely on fossil fuels (in the form of pesticides, fertilizers, and energy), is based on symbiosis and multicultural farming, and produces high-quality meats.
Management-Intensive Grazing is such a simple concept on the surface. The farmer divides his land into several dozen plots. He initially seeds all the plots with a variety of grasses that are allowed to grow wildly. Then he rotates animals through the plots.
The cycle of each plot begins with grazing cows at a time when the grass is at its "sweet spot." The cows pick and choose to eat whatever grass suits their needs - they're skilled grass connoisseurs - and as they graze, they fertilize the plot with their manure. Two days after the cows have feasted, the chickens and hens sanitize the plot by picking delicious grubs out of the cows' manure. They finish off whatever shards of grass has been left, all the while aerating the lot with their pecking. Then the lot is allowed to recover, free of animals, until is again at its "sweet spot," for the cycle to start over.