Grains are grass seed. Corn, wheat, rice, barley, sorghum, millet, oats, triticale, and rye are in the grass family, whose scientific name is Poaceae. The only exceptions are pseudocereals buckwheat and quinoa.
Corn is produced in the greatest quantity, followed by rice and wheat. A good explanation of why is in Michael Pollan's Omnivore's Dilemma, this decade's most important book about food production. The basic reason is corn is the raw material used to produce beef, chicken, pork, and even fish.
The corn you eat as a table vegetable, on or off the cob, is called "sweet corn." It is not included in agricultural statistics on corn. It is a specialty crop that makes up well under 1 percent of corn grown. Corn grown across the Midwest is called "field corn" or simply "corn." Humans cannot digest field corn (unless it is processed with lye, turning it into hominy). It was historically grown to be cattle food. We now use 40 percent of it to make fuel, primarily ethanol.
Corn is linked to petroleum in two ways. On the front end, petroleum provides irrigation water, fertilizer, and herbicides. On the back end, the price of petroleum determines the value of fuel. Ethanol becomes worth more when the price of gasoline goes up, causing farmers to plant more corn and less food crops. Thus, the price of petroleum indirectly affects the price of all meat and vegetables.
Americans spend only 9 percent of their income on food. That's less than citizens of any other country, and less than half what we spent 50 years ago. We spend the savings on cell phones and cable TV. In order to make that possible, the US government subsidizes the price of petroleum, thus food, through military operations paid for with debt. You can afford a cell phone now because your grandchildren will pay for your food some time in the future.
Our agriculture is becoming monocultural. Not only is corn the raw material for meat and fuel, we also use it to make sugar (high-fructose corn syrup), cooking oil, plastics, fabrics, and half those food additives with chemical names. A 2012 Midwestern drought caused the price of corn to go from its normal $4 a bushel to $8. The effect will be higher prices on half the things in your supermarket and fast food outlets. Prices will not go back down when corn returns to $4, thanks to the ratchet effect. Surplus money will go to the top 1 percent.
Contributing to the increase in corn price is the expiration of federal subsidies on 9/30/2012. Corn farmers had been getting $6 billion per year. They want it back. Perhaps they hope to get it by shocking consumers with higher prices.
Nearly all above-ground crops produce the same 2,000 pound yield per acre. Apples and zucchini, cotton, kumquats, lettuce, and wheat all yield 2,000 pounds per acre. Corn is the exception. It yields 160 56-pound bushels for 8.400 pounds per acre. Some Iowa farms get 300 bushels. When the price of corn is high, as it is now, a farmer can gross $1200-1500 per acre growing corn versus $500 for most crops. When the price of corn is normal, the farmer gets a normal $500. When the price is low, he needs welfare from Washington.