Friday, 13 May 2011

RE: Pre-Columbian raised field agriculture: a review

Umberto: Hello again, here goes Delphine Renard and Doyle McKey’s reply to my last post. I am hoping to make this blog an open space for discussion about the Amazon’s past – so I’ll be more than happy to post people’s comments and views on the subjects here reviewed or any other that you might want to put forward for discussion. If you have articles, reviews or announcements you would like to share with other ‘amazonists’ pass them on to me and I will include them in future entries. 

Delphine Renard and Doyle McKey:

Thank you for your interesting comments on our paper. We would like to address two points you made.

First, you consider that some of the hypotheses about functioning of raised-field agriculture are “contradictory” and regret that we don’t “take a position” in these cases.  We see this a bit differently. Some of these hypotheses apply more to some systems and others to other systems. We thus see these hypotheses as complementary rather than contradictory. An example of the difference in our viewpoints is seen, we think, in your criticism that we do not take a position on whether fallows were necessary or not. We do “take a position” on this point. Our “position” includes two points: (1) We think it likely that the need for a fallow period was variable among these systems, depending on soil fertility. The chinampas were built on quite fertile young soils, with volcanic influence and alluvial import. The underlying fertility of this starting material may explain how agriculture can be conducted continuously there. In areas with poorer soils, fallows may have been necessary. Also, pest buildup could well be more rapid in warm lowland sites; escaping pests might thus confer a greater advantage of incorporating fallows in such sites. (2) We think that experimental field studies so far have been of much too short duration to settle the question in any site. As you pointed out in one of your JAS papers, some of these experiments have also had methodological problems that call their results into question.

Secondly, you conclude that better drainage is the only thing all these systems have in common, and wonder why we didn’t conclude the same. We think this view is too narrow, and that different raised-field systems also have other things in common. One of these is the alternation in time and space of aerobic and waterlogged compartments of the ecosystem, which introduces more complexity in nutrient dynamics and could, as we point out in our review, increase nutrient availability to crops. Input of muck from flooded inter-mound areas onto mounds is one way raised-field agriculture could benefit from this, but there are other ways, for example, putting onto mounds mulch from waterlogging-tolerant vegetation that grew in the flooded spaces during a fallow period. We thus think that the mix of waterlogged and aerobic compartments could have been of functional importance in many different raised-field systems.

Finally, we would like to point out that raised fields, like terra preta, are not “magic bullets” for achieving sustainable agriculture, and it is wrong to consider them so. But they could be useful ingredients of solutions. Some of the criticisms leveled at raised-field rehabilitation projects merely reflect paradoxes that we will have to overcome in any attempt to make agriculture ecologically sustainable today—the loss of knowledge and social capital on which such agriculture depends. Transforming agriculture anywhere is going to be difficult. But this doesn’t make it any less necessary, and we don’t think it’s wise to conclude on the basis of studies so far that raised-field agriculture has nothing to offer.   

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