The Omnivore's Dilemma - Michael Pollan [97]
“What you want to do is graze a pasture right at this point here”—he tapped my pad sharply—“at the very top of the blaze of growth. But what you never, ever want to do is violate the law of the second bite. You can’t let your cows take a second bite of a grass before it has had a chance to fully recover.”
If the law of the second bite were actually on the books, most of the world’s ranchers and dairy farmers would be outlaws, since they allow their stock to graze their pastures continuously. By allowing cattle a second or third bite, the most desirable “ice cream” species—clover, orchard grass, sweet grass, bluegrass, timothy—weaken and gradually disappear from the sward, giving way to bald spots and to weedy and brushy species the cows won’t touch. Any plant wants to keep its roots and shoots roughly in balance, so grasses kept short by overgrazing lack the deep roots needed to bring water and minerals up from the subsoil. Over time a closely cropped grassland deteriorates, and in a dry or brittle environment, it will eventually turn into a desert. The reason environmentalists in the western United States take such a dim view of grazing is that most ranchers practice continuous grazing, degrading the land by flouting the law of the second bite.
Joel pulled a single blade of orchard grass, showing me exactly where a cow had sheared it the week before, and pointing out the finger of fresh green growth that had emerged from the cut in the days since. The blade was a kind of timeline, sharply demarcated between the dark growth predating the bite, and the bright green blade coming after it. “That’s the blaze of growth, right there. I’d say this paddock will be ready for the cows to come back in three or four more days.”
“Management intensive” it is. Joel is constantly updating the spreadsheet he keeps in his head to track the precise stage of growth of the farm’s several dozen paddocks, which range in size from one to five acres, depending on the season and the weather. This particular paddock, a flattish five acres directly behind the barn that is bordered to the north by a hedgerow and to the south by the creek and dirt road that links Polyface’s various parts and pastures like a crooked tree trunk, now took its place on the mental schedule. The sheer number of local variables involved in making such a determination hurt my head to consider, and help explain the difficulty of fitting intensive grazing into an industrial agriculture founded on standardization and simplicity. The amount of time it takes a paddock to recover is constantly changing, depending on temperature, rainfall, exposure to the sun, and the time of year, as does the amount of forage any given cow requires, depending on its size, age, and stage of life: A lactating cow, for example, eats twice as much grass as a dry one.
The unit in which a grass farmer performs and records all these calculations, deciding exactly when and where to move the herd, is a “cow day,” which is simply the average amount of forage a cow will eat in one day; for his rotations to work, the farmer needs to know just how many cow days each paddock will yield. Though it turns out that, as a unit of measurement a cow day is a good deal more rubbery than, say, the speed of light, since the number of cow days any given paddock can supply rises and falls in response to all the aforementioned variables.
As destructive as overgrazing can be to a pasture, undergrazing can be almost as damaging, since it leads to