Jeremy Cherfas recently interviewed me on Eat This Podcast, which has many interesting food- and agriculture-related interviews.
Earlier, Cherfas cofounded my favorite blog, the Agricultural Diversity Weblog, so I was delighted when he was the first to review my book. In Darwinian Agriculture I argued that crop rotation (with both crop diversity over time and lanscape-scale spatial diversity) often makes more sense than crop diversity within a field (intercropping). Jeremy's mostly-positive review points out that I neglected to discuss diversity within a species, such as growing a mixture of two or more wheat varieties. So I talk about that some in the podcast interview.
But in asking "how should we deploy crop diversity in space and time" both book and podcast implicitly assume that total usable diversity is limited. If there are currently only two wheat varieties that can be grown profitably in a given region, you have to choose between growing the same two-variety mixture every time you grow wheat, versus rotating (alternating) between them. (Growing them as a mixture further assumes they can be managed similarly, including planting and harvesting the same day, similar irrigation, etc. A rotation that alternates different wheat varieties could also include other crops or fallow years.)
If there are dozens of suitable wheat varieties, though, you could have lots of diversity both at different spatial scales and over time: different two-variety mixtures in different fields, without having to grow the same variety in the same field in successive years.
My main worry, though, is that world food security relies so heavily on just three crops (corn, wheat, and rice). In both the book and the podcast, I argue that farmers making rational decisions about their individual risks and benefits will collectively choose less crop diversity than we need to ensure global food security. I doubt that this example made it into Robert Frank's book (see last post), but the issues are analogous to those that caused the recent Great Recession.