Even if everything else were equal, it would still be difficult, even for a computer, to compare the nutrient value of bulky manures with that of bags of fertilizer. A truck will hold by volume a certain weight of a certain fertilizer, while manure on a manure spreader, from one load to another, might vary not only in plant nutrient analysis but also in weight, depending on moisture and the ratio of dung to bedding in each load. In other words, it is impossible to spread manure from a manure spreader with the same precision with which you can apply powdered or liquid fertilizer with a mechanical applicator. These calculations become critical when determining the net value of hauling manure from an animal factory. Someone has to pay the freight, and the amount of plant nutrients in a truckload determines how far you can haul it profitably. And based on the amount of nutrients in both materials by weight, it is much cheaper to haul fertilizers than manure. Fuel cost becomes part of the equation too, of course.

Most important of all, agronomists have not yet been able to agree on a precise figure for the value of organic matter and humus that manure adds to the soil. I doubt if a precise figure is possible. It gladdens my heart to think that organic matter in the soil is so priceless that not even science can put a dollar value on it.

But it is fun and instructive to muse on the relative value of manure versus chemical fertilizer—a good thing to contemplate. For example, let us muse that Farmer A milks forty cows on an organic dairy farm. He has lots of manure as a free by-product of his dairying—the amount varies, of course, but you can roughly figure at least 15 tons of manure and bedding for each milk cow and half that for calves and replacement heifers. The manure, in fact, is essential to his operation because it would be very difficult (if not impossible) for him to make a profit organically without it. Since he gets a premium for his organic milk, his manure is worth even more than it would be for the dairy farmer not selling organic milk. Let us say that non-organic farmers in his neighborhood routinely apply fertilizer that costs—in summer 2009, as I write—about $80 per acre. Last year it could have cost twice that. For every acre Farmer A fertilizes with animal manure and green manure instead, he saves that much money right off the whirling blades of his manure spreader. If he manures 100 acres that way, he's saved $8,000, less the hauling and labor, before he puts a milker on his first cow.

Farmer B, however, grows 1,000 acres of corn and soybeans. His situation is vastly different when it comes to making decisions about fertilizer. He must buy all of his. Let us say he is not close enough to an animal factory to make hauling manure cost-effective, even if he could buy it cheaper than chemical fertilizer. He must buy the chemical stuff instead, at least for the 500 acres of corn. We'll assume that he doesn't put fertilizer on his soybeans, as many farmers do not. At $80 per acre, he has already spent $40,000 on his corn crop before he even climbs on his planter. You can readily see why my friend with 8,000 acres just might be getting interested in a cattle feedlot even if the beef side of the business only breaks even. With 4,000 acres of corn, his fertilizer bill is in the $320,000 range. And what if next year fertilizer prices go up again? The cow manure to replace that fertilizer begins to look like a very hot commodity indeed.