This is the final part of a two-part review. You can find part 1 here.
So is there anything I don’t like about Darwinian Agriculture? Actually, yes. Intercropping and polyculture, which is usually taken to mean mixing different crop species in space (and sometimes animals too), is, in Denison’s view, not proven to be more productive than growing the component species on their own in rotation. Fair enough; too often the long-term comparisons over a full cycle or two of rotations haven’t been done. But he doesn’t consider how polyculture might affect year-on-year stability; in marginal systems, especially, that may be a more important consideration than total productivity. The same goes for what I would argue is one of the clearest ways in which imitating Nature might be a good idea: mixtures of varieties of the same crop.
Denison explores the reasons for the 1971 epidemic of Southern Corn Leaf blight in maize, and uses it to make some telling points. But having said that “this disaster is often used, rightly, to show the need for more genetic diversity within crop species,” and promising that he would return in later chapters to the question “which is more useful, diversity within fields or diversity among fields?” he doesn’t, at least not for diversity within a species.
Of course it isn’t fair to criticise an author for not covering a topic close to my own heart, but I do wish he had given at least some space to the question of intra-specific diversity as a perfectly good Darwinian response to the threat posed by pests and diseases: lack of diversity in the response to a threat is risky. This idea comes into the management of resistance to GMO plants, with a good discussion of the need for refugia of non-engineered plants as part of a strategy to delay the emergence of resistance. But as a more general mechanism, it gets short shrift, which is a shame. And it isn’t as if the evidence is lacking, at least for damping down yearly yield variability.
You could get the impression from this review that Ford Denison is long on the problems with agriculture and short on solutions. You would be wrong. In fact, some of his proposed solutions are so exciting I honestly wished I were just starting on a long research career. Boost the cooperation between legumes and nitrogen-fixing bacteria? Count me in. Figure out how to use plant-animal signals more effectively than always-on alarm pheromone? You bet. Ask in detail how this year’s crop could benefit next year’s? Yes please. Just because trade-off blind biotechnology and unthinking mimicry have so little to offer is no reason to despair.
Perhaps the most important thing Denison has to ask, in what is either true humility or unbridled academic chutzpah, is “What if my proposed core principles turn out to be wrong?” This is the central argument for his rider, on the need for a bet-hedging approach that allows ideas to compete. This, too, appeals to my confirmation bias. Simplistic, whizz-bang approaches suck the air out of the room, leaving less shiny ideas gasping, and nutrition, breeding and sustainability are three particularly vulnerable areas. Right now a squillionaire philanthropist, with, say US$30m to invest, has a couple of choices. Increase the donor budget for simplistic whizz-bangery by somewhere between 1% and 10% – nice, but hardly a big deal. Or double the budget for “other” approaches, which could indeed make a real difference.
You’ll have gathered that I think Darwinian Agriculture is the best non-fiction I’ve read in a long, long time. Anecdotally, others in the field seem to agree. The big question is, how to get those who make the big decisions, and who clearly don’t understand either ecology or evolution as they apply to agriculture, to pay attention. Answers in the comments, please.