Sunday, October 26, 2014

No-till study illuminates part of the problem space

An extensive review article published on Nature's website, and described on the UC Davis news website, concludes that no-till farming only results in yield increases in dryland areas, and then only when combined with crop rotation and residue retention, and that it results in a yield reduction in moist climates.

While I have no reason to doubt the conclusions of the co-authors, as far as they go, I do have some concerns as to the scope of the comparisons they've made. However, not having read the full article, I can only pose questions and suggest considerations which may offset or even outweigh the modest yield reductions in moist climates, which they've noted.

It's hard to know where to start; this is such a complex subject. As practiced in western countries, no-till usually also means weed suppression by use of herbicides. It may or may not include residue retention, but if the residue is retained it is likely to be in rough form rather than finely chopped, or retained as the dung of the animals that grazed on it after harvest, never as well-distributed as the residue was in the first place. It may or may not include crop rotation, but almost certainly does not include polyculture (also called intercropping), which has become an all too rare practice.

Allow me to back up a bit, and consider an assumption, as expressed by one of the co-authors: "The big challenge for agriculture is that we need to further increase yields but greatly reduce our environmental impacts." Certainly we need to vastly reduce the environmental damage being done by modern agriculture, but just how much do we really need to increase yields. Population growth estimates not taking into account the predictable reduction in fecundity that accompanies prosperity will result in alarmism, but the reality is that what benefits the global economy has to offer the poorest are slowly finding their way to every corner of the planet, and it's reasonable to think that the world population will plateau, if not at ten billion, then perhaps at eleven or twelve billion. Of course, there is hunger now, even starvation, much of it happening in the dryland areas surrounding the Sahara. Yield increases in this region would be particularly helpful, but are complicated by competing uses, as fuel and as animal feed, for the residues which should be left in the fields. Realistically, the bottom line comes down to this: Can we afford to sacrifice long-term fertility for short-term gains in yield?

That question begs another, does the article published in Nature include any long-term studies, by which I mean at least twenty years, preferably longer? Not only does tillage gradually burn through (literally oxidize) soil organic matter, eventually effecting water absorption and retention and nutrient availability, and increasing the energy required for ongoing tillage as the soil becomes denser, but also it takes time for an ecosystem of animals and microbes to develop that can efficiently incorporate crop residues into the soil, particularly in fields that have a long history of routine tillage.

Were any options other than simply leaving residue in the field or grazing considered? Are there any cases of fine-chopping residue during harvest? What about initially removing everything but the stubble and returning it after processing it through animals (as feed), through anaerobic digestion (producing methane gas for fuel), and/or through composting?

Were the costs of production considered? No-till generally involves the cost of herbicide and its application, but tillage is an energy-intensive operation, and over the long term diesel will only become more expensive. If the fuel must be grown, shouldn't the percentage of the overall crop area required to grow it be deducted from the net yields? How does no-till look after performing that calculation?

Nor have we yet seen the full benefits of no-till, because we have yet to develop equipment appropriate to it. Western civilization is so accustomed to tillage that we tend to be blind to assumptions made stemming from a fundamental assumption that tillage is the foundation of agriculture. We see equipment built to perform tillage at work and don't think twice about it. There have been some adaptations – spraying equipment that is only as heavy at it needs to be for that purpose, and oversized tires for heavier equipment – but nearly all of the equipment in use, even in no-till operations, still deals with land as a bulk commodity, measured in acres per hour, rather than at the level of detail required to, for example, selectively harvest one crop while leaving several others, intermingled with it, undisturbed.

Until recently, this could only be accomplished by hand labor, but with the advent of computing using integrated circuits, and its combination with sensory hardware, sophisticated mechanisms, and software to match the problem space (together comprising the field of robotics), the question of whether such work can be mechanized has been transformed into one of how soon. A significant obstacle to this development is cultural, in that we've all but forgotten how to tend land in this manner, and may have to reinvent the practice in order to program the machines. Certainly many in our agricultural colleges and universities will require remedial education.

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