Category: Indigenous knowledge systems

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Detoxifying cassava

Strategies that minimize one risk…may augment another risk… Peasant farmers are perfectly conversant with such linkages. The neglect of peasant agriculture by both donors and governments is among the deeper causes of current crises, along with the increasing inequality that deprives them of secure tenure to land and other resources, reducing benefits they can expect to receive from stewardship of these resources.

That comes towards the end of a lengthy, information-dense and closely argued paper on cassava’s domestication, evolution and chemical ecology by Doyle MacKey and others. ((McKey, D., Cavagnaro, T., Cliff, J., & Gleadow, R. (2010). Chemical ecology in coupled human and natural systems: people, manioc, multitrophic interactions and global change Chemoecology, 20 (2), 109-133 DOI: 10.1007/s00049-010-0047-1)) Coincidentally — or perhaps not — McKey also has a paper out just now on the evolutionary ecology of vegetatively propagated crops in general. ((McKey, D., Elias, M., Pujol, B., & Duputié, A. (2010). The evolutionary ecology of clonally propagated domesticated plants New Phytologist, 186 (2), 318-332 DOI: 10.1111/j.1469-8137.2010.03210.x)) But that’s something for a future post, perhaps. Back to cassava.

Well, as I say, there’s a lot of stuff in the paper, but let me focus on a just a couple of things here. Some cassava varieties are high in poisonous cyanogens, requiring laborious and time-consuming processing for detoxification, which is almost exclusively done by women and, according to at least one anthropologist, serves to control them, “by limiting their freedom of action, in male-dominated societies.” So let’s replace those high-cyanogen, “bitter” varieties with low-cyanogen, “sweet” varieties, right?

Well, not so fast. ‘‘Interestingly enough, the women that are the custodians of this crop do not perceive the processing or the toxin to be a problem.’’ Bitter manioc is in fact better for food security for at least three reasons: it is protected against pests; immediate processing deters thieving; and the value added through processing reduces the social obligation to share. Overall, therefore, “processing bitter manioc is viewed as a useful and valorizing activity.”

But there are regular epidemics still in some parts of Africa of the paralytic disease konzo, which is “associated with several weeks of almost exclusive consumption of insufficiently processed bitter cassava.” Surely low-cyanogen varieties would be welcome there?

Again, the authors are dubious. They point out that agronomic practices, in particular careful nutrient management, together with adequate processing and a reasonably protein-rich diet are perfectly sufficient to manage the toxicity problem, and in fact normally do so. It is mainly when socioeconomic stability breaks down that konzo erupts. As they trenchantly put it: “This crop needs peace.” And reasonable rainfall. Drought stress tends to increase cyanogen levels. Plus, “[a]s they face food shortage, people may then take short cuts in processing bitter manioc.” In both cases, new, faster, more efficient detoxification methods will have a bigger impact than sweet varieties, with their greater susceptibility to pests.

In general, cassava is expected to be comparatively little affected by climate change, and is being promoted in some quarters as a “food for the future.” Fair enough, say the authors, but this

…will need to be accompanied by the necessary education for processing, as planting less bitter cultivars appears not to be a solution. Farmers have good reasons for preferring bitter varieties.

Indeed they do. So let me end with another heady quote, again from the concluding section of the paper, a little further on from the quote I started with.

We must have the humility and the broad vision to accept that our science can provide essential pieces, but only pieces, of viable solutions. ‘‘Modern’’ science can work in creative ways with folk knowledge. But no technological fix is a ‘‘magic bullet’’.

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Livestock reverse desertification

There’s something delicious about received wisdom being overturned. For example, you’ll hear it said, categorically, that livestock turn fragile landscapes into desert; they eat the plants binding the soil, and their hooves cut up the surface and promote erosion. But it ain’t necessarily so.

Operation Hope, a Zimbabwean NGO and winners of $100,000 Grand Prize in the Buckminster Fuller Challenge, has

[T]ransformed 6,500 acres of of parched and degraded grasslands in Zimbabwe into lush pastures replete with ponds and flowing streams – even during periods of drought.

The quote is from a write-up in Seed magazine, which gives lots of details of the story. In essence, the key to livestock and grasslands is time, not numbers. If animals are on the land too long, their hooves do indeed powder the soil and they do overgraze. But if they are free to move on, or are moved by herders, moderate trampling allows rain to percolate into the soil, rather than run off and cause erosion. It also improves contact between seeds and soil, promoting germination. And dung and urine return plant matter to the soil to increase fertility and sequester more carbon, without becoming pollutants.

Operation Hope grazes animals in one spot for a maximum of three days, and they do not return for at least nine months, mimicking the natural movements of large herbivores on the savannah. At night they are protected from predators in portable kraals, which are also mobile to prevent a build-up of dung and urine. The effects are impressive. (“Animal-treated” field on the right, conventionally managed field on the left. Image courtesy Buckminster Fuller Institute”)

What’s interesting, and this is explored in much more detail in the Seed article, is that this kind of ecosystem thinking, which requires human knowledge and ingenuity to tackle complex problems, could have applications well beyond range management. Allan Savory, the scientist behind Operation Hope and the Africa Centre for Holistic Management, is hard on the Green Revolution.

“We posit the necessity of a new ‘Brown Revolution’, based on the regeneration of covered, organically rich, biologically thriving soil, and brought to fruition via millions of human beings returning to the land and the production of food.”

Of course, that’s hard work. But it is also surely much more interesting and fulfilling.

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How many varieties are there in the world, mom?

Back at the day job, we are often asked by journalists and others how many different types, or varieties, of this or that crop there are in a country, or indeed the world. And, with help from our friendly crop experts, we have tried to provide answers. But it is as well to remind ourselves sometimes how slippery the question is. Because, to paraphrase Bill Clinton, it really does depend on what your definitions of “different” and “variety” are. For example, take rice in a particular part of Thailand, as the authors of a recent paper in GRACE did. ((Oupkaew, P., Pusadee, T., Sirabanchongkran, A., Rerkasem, K., Jamjod, S., & Rerkasem, B. (2010). Complexity and adaptability of a traditional agricultural system: case study of a gall midge resistant rice landrace from northern Thailand Genetic Resources and Crop Evolution DOI: 10.1007/s10722-010-9579-z))

They looked at 20 accessions of a single landrace, defined as a “geographically and ecologically distinctive population, identifiable by unique morphologies and well-established local name.” That is, these 20 samples, though collected from different farmers and even villages, all basically looked the same, and were recognized as belonging to the same type by farmers, who gave them all the same name — Muey Nawng.

But the authors found significant, non-random, patterned variation within the material, not only in microsatellite markers, which wouldn’t perhaps be so bad, but also in endosperm starch type, days to heading and, interestingly, gall midge resistance. So how many varieties were there among the 20 samples of Muey Nawng? Answers on a postcard, please.