Iowa's fields require the energy of 4,000 Nagasaki bombs every year.

           

        we humans take 40 percent of the globe's primary productivity every year. You might have assumed we and our livestock eat our way through that volume, but this is not the case. Part of that total—almost a third of it—is the potential plant mass lost when forests are cleared for farming or when tropical rain forests are cut for grazing or when plows destroy the deep mat of prairie roots that held the whole business together, triggering erosion

           

        A functioning grassland prairie produces more biomass each year than does even the most technologically advanced wheat field. The problem is, it's mostly a form of grass and grass roots that humans can't eat. So we replace the prairie with our own preferred grass, wheat. Never mind that we feed most of our grain to livestock, and that livestock is perfectly content to eat native grass. And never mind that there likely were more bison produced naturally on the Great Plains before farming than all of beef farming raises in the same area today.

          

          On average, it takes 5.5 gallons of fossil energy to restore a year's worth of lost fertility to an acre of eroded land—in 1997 we burned through more than 400 years' worth of ancient fossilized productivity, most of it from someplace else. Even as the earth beneath Iowa shrinks, it is being globalized.

           

          On average, about 10 percent of all other biomes remain in something like their native state today. Only 1 percent of temperate grasslands remains undestroyed.

           

           Plato wrote of his country's farmlands:

          What now remains of the formerly rich land is like the skeleton of a sick man. . . . Formerly, many of the mountains were arable. The plains that were full of rich soil are now marshes. Hills that were once covered with forests and produced abundant pasture now produce only food for bees. Once the land was enriched by yearly rains, which were not lost, as they are now, by flowing from the bare land into the sea. The soil was deep, it absorbed and kept the water in loamy soil, and the water that soaked into the hills fed springs and running streams everywhere. Now the abandoned shrines at spots where formerly there were springs attest that our description of the land is true.

          

         We have a clear answer. In about 1960 expansion hit its limits and the supply of unfarmed, arable lands came to an end. There was nothing left to plow. What happened was grain yields tripled. 

           

         The accepted term for this strange turn of events is the green revolution, though it would be more properly labeled the amber revolution, because it applied exclusively to grain—wheat, rice, and corn. Plant breeders tinkered with the architecture of these three grains so that they could be hypercharged with irrigation water and chemical fertilizers, especially nitrogen. This innovation meshed nicely with the increased “efficiency” of the industrialized factory-farm system. With the possible exception of the domestication of wheat, the green revolution is the worst thing that has ever happened to the planet.

           

         The common assumption these days is that we muster our weapons to secure oil, not food. There's a little joke in this. Ever since we ran out of arable land, food is oil. Every single calorie we eat is backed by at least a calorie of oil, more like ten. In 1940 the average farm in the United States produced 2.3 calories of food energy for every calorie of fossil energy it used. By 1974 (the last year in which anyone looked closely at this issue), that ratio was 1:1.

           

          Nitrogen can be released from its “fixed” state as a solid in the soil by natural processes that allow it to circulate freely in the atmosphere. This also can be done artificially. Indeed, humans now contribute more nitrogen to the nitrogen cycle than the planet itself does. That is, humans have doubled the amount of nitrogen in play.

           

          Rainfall and irrigation water inevitably washes the nitrogen from fields to creeks and streams, which flows into rivers, which floods into the ocean. This explains why the Mississippi River, which drains the nation's Corn Belt, is an environmental catastrophe.

           

          America's biggest crop, grain corn, is completely unpalatable. It is raw material for an industry that manufactures food substitutes. Likewise, you can't eat unprocessed wheat. You certainly can't eat hay. You can eat unprocessed soybeans, but mostly we don't. These four crops cover 82 percent of American cropland. Agriculture in this country is not about food; it's about commodities that require the outlay of still more energy to becomefood.

           

         The Department of Agriculture says the ratio is closer to a gallon and a quart of ethanol for every gallon of fossil fuel we invest. The USDA calls this a bargain, because gasohol is a “clean fuel.” This claim to cleanness is in dispute at the tailpipe level, and it certainly ignores the dead zone in the Gulf of Mexico, pesticide pollution, and the haze of global gases gathering over every farm field.

           

          Green eaters, especially vegetarians, advocate eating low on the food chain, a simple matter of energy flow. Eating a carrot gives the diner all that carrot's energy, but feeding carrots to a chicken, then eating the chicken, reduces the energy by a factor of ten. The chicken wastes some energy, stores some as feathers, bones, and other inedibles, and uses most of it just to live long enough to be eaten. As a rough rule of thumb, that factor of ten applies to each level up the food chain, which is why some fish, such as tuna, can be a horror in all of this. Tuna is a secondary predator, meaning it not only doesn't eat plants but eats other fish that themselves eat other fish, adding a zero to the multiplier each notch up, easily a hundred times, more like a thousand times less efficient than eating a plant.

           

         This is fine as far as it goes, but the vegetarian's case can break down on some details. On the moral issues, vegetarians claim their habits are kinder to animals, though it is difficult to see how wiping out 99 percent of wildlife's habitat, as farming has done in Iowa, is a kindness. In rural Michigan, for example, the potato farmers have a peculiar tactic for dealing with the predations of whitetail deer. They gut-shoot them with small-bore rifles, in hopes the deer will limp off to the woods and die where they won't stink up the potato fields.

          

          Eighty percent of the grain the United States produces goes to livestock. Seventy-eight percent of all of our beef comes from feed lots, where the cattle eat grain, mostly corn and wheat. So do most of our hogs and chickens. The cattle spend their adult lives packed shoulder to shoulder in a space not much bigger than their bodies, up to their knees in shit, being stuffed with grain and a constant stream of antibiotics to prevent the disease this sort of confinement invariably engenders. The manure is rich in nitrogen and once provided a farm's fertilizer. The feedlots, however, are now far removed from farm fields, so it is simply not “efficient” to haul it to cornfields. It is waste. It exhales methane, a global-warming gas. It pollutes streams. It takes thirty-five calories of fossil fuel to make a calorie of beef this way; sixty-eight to make one calorie of pork.