A Sustainable Steak?: The Mathematics of Nutrient Cycles

I spent the morning reading Adam Merberg’s fascinating blog, http://saywhatmichaelpollan.wordpress.com/ Merberg often comments here at eatingplants.org and I’d encourage a careful look at whathe’s up to. In any case, this post comes directly from what I learned from Merberg’s work. Thank you, Adam.

“A truly sustainable agriculture,” Michael Pollan writes on his blog, “will involve animals.” The justification for this claim, one that’s been further popularized by Lierre Kieth’s The Vegetarian Myth and Simon Fairlie’s Meat: A Benign Extravagance, is that animals “complete the nutrient cycle.” Because ruminant animals return to the earth the nutrients they take from it, and because the process is driven exclusively by solar power, Pollan and others are able to justify meat eating on environmental grounds. “Eating a steak at the end of a short, primordial food chain comprising nothing more than ruminants and grass and sunlight,” Pollan writes, “is something I’m happy to do and defend.” The vast majority of the sustainable food movement would certainly agree.

But Pollan, as well as the sustainable food movement, may very well be defending the indefensible. The most conspicuous example of a supposedly high-functioning nutrient-cycling, diversified farm is Joel Salatin’s Polyface, Inc.–made famous by Pollan’s Omnivore’s Dilemma.  Salatin’s meat, according to Pollan, looks “an awful lot like the proverbial unattainable free lunch.”  However, according to Adam Merberg, a PhD student in mathematics at Berkeley and author of a blog that mathematically scrutinizes Pollan’s major claims, lunch from Polyface is significantly more costly than it seems. The story of the nutrient cycle, it turns out, is a bit more complex than Pollan claims it to be.

Pollan’s steak actually has a lot to do with chickens. Merberg notes that Polyface produces over 12,000 broiler chickens year.  These birds, as Pollan describes their role, do more than meet local demand for chicken flesh.  They’re essential to enhancing soil fertility. Without chicken poop, fertilizer would have to be imported into the system. The catch here is that Polyface (according to Merberg’s estimation) imports roughly 144,000 pounds of feed a year–mainly in the form of corn, soy, and oats–in order to nurture their clucking fertilizer machines (which produce lush pastures to keep the cows well fed).

What this means is that the nutrients that chickens return to the soil are outsourced, leaving a plot of land somewhere outside the Polyface cycle devoid of its nutrients. Pollan writes that, “The chief reason Polyface Farms is completely self-sufficient in nitrogen is that a chicken, defecating copiously, pays a visit to virtually every square foot of [the pasture] at several points during the season.” But that nitrogen, of course, came from elsewhere.

This hidden cost effective torpedoes the idea not only of a closed system, but a free lunch as well. Given that such “self sufficiency” is directly due to externalized environmental degradation (growing corn and soy), Merberg calculates that Polyface ultimately consumes more calories than it produces.  The farm (again Merberg stresses that these are estimates) imports 244,800,000 calories a year and it produces 171, 368, 236–leaving it with a net loss of over 73,000,000 calories of food energy. To convince himself these these numbers were not radically off the mark, Merberg actually asked Salatin at a recent Berkeley conference this simple question: “Do you get more out of the farm than you put into it?” Merberg, cited the environmental cost of grain and, on this basis, surmised the answer was “no.”  To his surprise, Salatin responded, as Merberg puts it, “that I was exactly right.” Salatin added (in Merberg’s paraphrase) “that other people say his farm is sustainable, but he doesn’t advertise it as such.”

In fairness to Polyface, it does remarkably better than industrial methods of animal production. But, to be sure, it’s offering no free lunch, nor is it “truly sustainable.” The nutrient cycle spins not only on sun, but on energy purloined from grain–energy that the animals are not able to return to the cycle.  Merberg’s assessment of his own findings is admirably conservative. He never concludes that we should all run off and eat grain–in fact he treads lightly around the entire vegetarian/vegan debate, evidently awaiting more detailed information before making comparisons.  There’s no denying, though, that animals raised in rotational grazing systems fail to “complete the nutrient cycle.”

“Every time we take food–whether it be from plant or animal source–from a farm,” Merberg writes, “we’re taking nutrients away.” From a narrowly defined idea of environmentalism, it seems safe to say that we need to minimize the impact of what we exact. I find it hard to believe, based in part on my assessment of Merberg’s work, that a pound of flesh could ever cost less (environmentally) than a bushel of grain.