I am painfully aware of the risk we run here at the Agricultural Biodiversity Weblog of becoming single-issue bores.1 To a hammer, everything is a nail. And if your thing is agrobiodiversity, you’ll naturally be tempted to think that every problem can be solved by the judicious application of an agrobiodiversity thwack. How refreshing it must be to occasionally think against the grain, and question your most cherished assumptions. That possibility is why — apart from my native contrariness — I so enjoyed a recent paper in Field Crops Research very appropriately entitled “Conservation agriculture and smallholder farming in Africa: The heretics’ view.”2 Even though it didn’t really have much to do with agricultural biodiversity.
Conservation agriculture (CA), or direct-seeding mulch-based cropping (DMC), is a package of crop management practices — basically, no mechanical soil disturbance, plus permanent organic soil cover, plus crop rotation3 — that is being forcefully promoted by numerous research and extension systems around the world, backed by various international agricultural development agencies, as the alternative to conventional practices. There was a world congress on it recently. Its main aim is to prevent soil degradation, in particular organic matter and nutrient depletion, and cut back on labour and other inputs, while of course maintaining or increasing yields and yield stability.
The problem, according to the paper, is that the evidence for these benefits is at best ambiguous, at least from Africa. In the mixed cropping systems of semi-arid Africa, the opportunity cost of retaining crop residues is often too high. Yields are likely to decline in the short term (though they may well rise in the long term). The labour burden on women may well increase, and overall it stays the same. Reduced tillage on its own has little effect on soil fertility. It is unclear whether CA allows reductions in fertilizer use. Increased soil biological activity under CA may in fact be detrimental to crop production. And so on. No wonder adoption has been limited in Africa. The only really sure thing is that DMC reduces soil erosion, and you see the benefits of that in the long term.
That may well be enough to warrant the use of CA in some “socio-ecological niches,” and CA proponents should be trying to identify what those might be, rather than pushing it as an all-purpose solution. It is no panacea, no silver bullet, the authors contend, piling on the cliches a bit. A lesson there for all one-issue bores. Not all problems are nails, even if all you have in your hand is a hammer. Now, what can us agricultural biodiversity bores learn from it?
- Risk? Becoming? You’re a bit further down that road than you seem to think, bud. Ed. [↩]
- Giller, K., Witter, E., Corbeels, M., & Tittonell, P. (2009). Conservation agriculture and smallholder farming in Africa: The heretics’ view. Field Crops Research. DOI: 10.1016/j.fcr.2009.06.017. [↩]
- Ha, you see, there is agrobiodiversity involved after all! Thwack! [↩]