Science Forums 2

[gaudencio]

Originally Posted by gaudencio
>>Moreover, it seems obvious that the top layer in that photo HAS been tilled, due to the random angles of the pieces.
>Maybe this recent activity was not in keeping with the traditional way of tending those "mounds." These days don't the locals harvest the TP, rather than grow stuff on it?
Agreed - I actually deleted a sentence where I wrote exactly that because it confused the message I was trying to get across, and I was worried it was sounding a bit incoherent anyway
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>But I think the prevention of leaching is the most important function of the shards in that harsh driving-rain environment.
Is there any kind of consensus on this? Have any experiments been done?

As for the theory about using the sherds/shards as a mulch, it's convincing, but there are a few issues. Firstly, for mulch to be effective it would have to be a complete covering - as you said, a kind of pot-sherd pavement. This is not what's shown in the photo; there is not a succession of dense, evenly spaced layers. There is only one dense "base" layer (with a few intriguing little shards underneath it which we'll ignore for now). Of course, it's possible they also used organic material with the sherds, but it seems unlikely to me.
Secondly, if I understand correctly, the charcoal and organic content are only a fairly small (if prominent) part of the soil. The rest is actual soil - identical to other soil in the area. If they were simply piling organic material, charcoal and potshards in successive layers, the soil would not contain soil - if you catch my meaning. Of course, over time the beasties would certainly mix it all up, but I find it hard to imagine they would do so to such an extent. What I'm trying to say is that they must have been piling soil on top as the layers progressed - whether it was all done in one go, or over a period of years. If we agree on this, then where would they have got the soil from if the ground were covered in sherds? It's not feasible that they farmed it from the surrounding area for all sorts of reasons.
Finally, as an (admittedly poor) amateur gardener, I find the prospect of direct sowing of seed into the proposed top layer rather unlikely. For the scenario which you suggest to be true, they would be sowing seed into a mix of sterile charcoal and bits of old pot, which I don't think would be conducive to good growth, though I may be mistaken on that since I've never tried.

I do still tend toward the idea that they built the soil as it is pretty much from scratch. Another good reason for this that's just occurred is that the original soil is so poor that during the early years they would not have been able to support the kind of size of population we suspect they did. I'm inclined to think terra preta only becomes that fertile when it reaches such a large depth. Therefore, we're left with the idea of people going out from one village and "colonising" another area by turning barren soil into terra preta. They could have gone out, a few men, subsisting on native vegetation and wild animals, and spent a year or two preparing the earth in the way I've suggested: digging down, laying the charcoal and the pot sherds loosely in layers. Though I admit this is my imagination running away with itself, and the idea of a natural evolution of the land over time is certainly more in keeping with "peasant" methods. If nothing else, it seems unlikely they would have transported the enormous amounts of pot sherds required rather than making them on site - and if they were made on site solely to dig in the earth, they wouldn't have been decorated. By the way, I think the fact that they are decorated precludes your idea of a "clay paste" spread over the burning organic matter.

OK....time for a breather. Sorry if that seems a little incomprehensible. This terra preta mystery has the potential to set off all sorts of ideas. And yes, any moderator who chooses to can incorporate the thread I started into this one if they want.

Gaudencio