Perennial grains debate

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Thanks to Billy Kingery for calling my attention to a recent paper by Chris Smaje, titled "The Strong Perennial Vision: A Critical Review", published in Agroecology and Sustainable Food Systems. The same journal published responses by Steve Gliessman and by Timothy Crews et al., to which Chris has responded on his blog, Small Farm Future.

These authors have probably thought about these issues more deeply than I have. And I don't want to try the patience of a couple of coauthors who are waiting for revisions on papers. So, for now, I'll just make a few comments on Chris's paper.

Among his points are 1) "there is no reason to suppose that lower-yielding perennial cereal crops cannot play a significant role in the sustainable food systems of the future" but 2) it's unrealistic to expect that they won't be lower-yielding. I tend to agree with both points. In my book, arguing for a diverse agricultural-research portfolio, I wrote:

"As explained in Chapter 7, I have my doubts about perennial grain crops. But do we really want to focus 100% of our grain-breeding efforts on annuals?"

One argument against claims that perennial grains will probably have lower yield is that apples sometimes allocate as much of their photosynthate to fruit as annual grains do to seed, as noted in a paper by Van Tassel et al. Chris points out that the apple trees in question were "physically supported and on strongly dwarfing rootstocks-- [and] are rarely grown commercially for [more than 10 years]." Chris's point is that this apple system isn't reliable evidence that perennial grasses could have high allocation to grain. I agree, but how much could we push the protein and calorie yield of tree crops? For example, could almonds be bred and managed to match the yields of annual grains? Even dwarf trees are taller than most weeds, so weed control could rely more on mowing and/or cover crops than erosion-promoting tillage or herbicides.

Chris notes that:

"some perennials (often C-strategists) can undoubtedly outperform some annuals in yearly resource capture, and this has been shown empirically in some cases, for example, in comparisons of Miscanthus with maize, alfalfa with soybeans, and perennial with annual sorghum (Piper and Kulakow 1994; DeHaan et al. 2005; Dohleman and Long 2009)"

but questions how much "breeders can manipulate plant allocation" to put extra resources acquired by perennials into seeds. He discusses this issue in some detail, but this still seems like an open question. Key to his arguments is Grimes' classification of plant strategies as competitive, stress-tolerating, or disturbance-adapted. If these strategies are really discrete and reflected throughout a plant's genome, I guess it would be hard to change. But given the apparent ease of transitions between annual and perennial (Silvertown and Dodd, 1966, cited by Smaje) or unicellularity to simple multicellularity, I suspect that it may not be too hard to change these strategies through plant breeding.

This wouldn't eliminate tradeoffs between individual-plant competitiveness and whole-crop yield, however. As Chris's paper states:

"It may indeed prove possible to select for high seed allocation in short-lived, C-strategy perennials whose growth habit enables them to accumulate more photosynthate than their annual counterparts, thereby simultaneously funding seed production and perennation. But, as Van Tassel (2012) concedes, these plants will be less competitive than co-extensive wild or weedy species--suggesting that the margin for cultivating them without resort to irrigation, tillage, fertilization, pesticide application and other such practices that perennial cereal cultivation aims to circumvent may be thin at best."

There's much more, including comments on sociological issues, so I expect this paper (and responses to it) will stimulate a lot of discussion.

Videos of my talks

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My recent talk in Dublin, hosted by by the Irish agricultural-research agency, Teagasc, is now available on YouTube. Unfortunately, the photographer apparently thought video of me talking and the audience listening was more interesting than my data slides. Maybe it was a mistake to wear a tie. The Q&A session, where I respond to questions about organic farming and genetic engineering, didn't rely on slides, so might be more interesting.

Previous videos that show my slides well include:

* My 2013 lecture series at the International Rice Research Institute .

* My 2013 department seminar at UC Davis.

* My 2010 keynote talk at the Applied Evolution Summit.

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. My book argues 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.

The Darwin Economy

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That's the title of Robert Frank's latest book. Like my book, Darwinian Agriculture, it emphasizes cases where individual and group interests are in conflict. I suggest reversing past natural selection for traits that make individual crop plants more competitive, at the expense of whole-crop yield or water-use efficiency.

Similarly, Frank suggests that people make individually-rational choices that leave everyone worse off. For example, how much risk should an individual accept for a higher-paying job? Beyond a certain income, a higher salary mainly increases ones relative status. Buying a relatively more expensive house gets you into a neighborhood with better schools, but it doesn't increase the total number of kids who get to go to that school. So, more workplace injuries, but no overall improvement in education. He suggests progressive taxes on consumption rather than income.

That's the title of a review Andy McGuire and I just published (online now) in Global Food Security.

Thanks, Joan!

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Joan Strassman, known for her research on cooperation in Dictyostelium, mentioned my book (and my research on individual-vs-community tradeoffs in solar tracking by alfalfa), in a recent talk at a meeting on "collective behavior", sponsored by the National Academy of Science. Thanks to Will Ratcliff for the photo.

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On the Ohio Investor Network, Paul Meagher has a good summary of my book's critique of biotechnology's exaggerated claims, from the perspective of a potential investor.

Emma Marris and I shared the stage at a recent event at Washington State University, organized by Andy McGuire. Emma argued that "hands off wilderness" and "preserving natural ecosystems in their 'pristine' state are incompatible. If keeping species from going extinct is more important than keeping them where they were in 1491 (or earlier, presumably, outside the Americas), then we should bet-hedge with a variety of approaches to conservation. Watch for her upcoming op-ed.

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Open access week Oct. 20-24

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Just Royal Society publications, unfortunately, but now's your chance to get three papers I published with Toby Kiers over the years:


Sanctions and mutualism stability: why do rhizobia fix nitrogen? (2002)


Human selection and the relaxation of legume defences against ineffective rhizobia (2007)

Inclusive fitness in agriculture (2014)

...or some of those other Royal Society papers you've been craving.

In Darwinian Agriculture, I argued that accepting tradeoffs rejected by past natural selection is key to past and near-future crop improvement, whereas novel phenotypes never tested by natural selection may eventually make major contributions. In this post, I will briefly discuss two recent papers relevant to this hypothesis.

Lee DeHaan and David Van Tassel published "Useful insights from evolutionary biology for developing perennial grain crops", in American Journal of Botany, while Lin et al. published "A faster Rubisco with potential to increase photosynthesis in crops" in Nature.

Perennial plants often develop more extensive root systems than annuals, reducing the risk of erosion. Well-managed perennial forages (pastures and hay fields) are arguably our most-sustainable agricultural system, supplying milk, meat, wool, and leather, and often getting most of their nitrogen from symbiotic rhizobia bacteria (the main focus of my own research) rather than external inputs.

The Land Institute, where DeHaan and Van Tassel work, has been attempting to develop perennial grain crops. I have argued that greater investment of photosynthate or nitrogen in roots will usually leave less of these limiting resources for grain (seeds). All else being equal, DeHaan and Van Tassel apparently agree:

"where annual crops can use a similar amount of water, light, and nutrients as the perennials... annuals will indeed have greater yield potential"
But they have argued (and I agree, on p. 97 of my book) that perennials may sometimes capture more of these resources than annuals can. The last chapter of my book, on diversity and bet hedging, therefore included perennial grains as an example of high-risk approaches deserving some funding.

The potential of perennials to photosynthesize more months per year than annuals also implies using water more months per year, but their superior root systems can sometimes help water soak into the soil rather than being lost to runoff.

Actual results so far are somewhat discouraging, however. DeHaan and Van Tassel cite a paper by Culman et al., which found greater above-ground biomass in a perennial grass, kernza, relative to wheat. So it might be a better forage than wheat, but its grain yield (with moderate fertilizer) was only 4% that of wheat in year 1 and 39% in year 2. So it would take about 5 acres of kernza to produce as much grain as 1 acre of wheat. Where are those extra 4 acres (and the water to irrigate them) going to come from? Or can we realistically expect significant yield increases without losing the benefits of perenniality?

I have argued that while some tradeoffs (e.g., root vs. grain) constrain crop improvement, other tradeoffs can represent opportunities. For example, the fastest versions of the key photosynthetic enzyme work best at CO2 concentrations greater than atmospheric. Lin et al. transferred genes for one of these enzymes from cyanobacteria into tobacco. The resulting plants grew more slowly than unmodified tobacco, even at 9000 ppm CO2 (atmospheric is now 400 ppm). So this looks like a step in the wrong direction, but it's only a first step. The cyanobacterial enzyme works well in cyanobacteria because they also have a CO2-concentrating mechanism. Some plants, including corn, have different CO2-concentrating mechanisms. See "The evolutionary ecology of C4 plants" for an interesting discussion of how these mechanisms evolved in plants. If someone could combine the faster cyanobacterial enzyme with a plant or cyanobacterial concentrating mechanism, they might achieve significantly greater photosynthesis.

That could take a decade or more, but it's worth noting that perennial grains have been a significant focus of the Land Institute for most of their 38-year history.

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