I share here a couple of posts by Sean and Gerry from the terra preta list and my responses. These help to refine aspects of the corn stover hypothesis.
#2? What nutrients does the ash provide? The soil is already very alkaline and white ash from complete combustion of any biomass is very alkaline. I do not believe either, that ash is a reasonable substitute for plant nutrients like Nitrogen-N, Phosphorus-P, Potassium-K, Sulfur-S, Calcium-Ca, Iron-Fe, Magnesium-Mg, etc.
Burning is used in all primitive agriculture through the method of ‘slash and burn’ to release nutrients captured by the biomass back unto the surface. It is in the form of ash and this means that most of it is very soluble and easily leached away. Biochar would likely be much more retentive as the evidence suggests.
Charcoal in the original Terra Preta is in large chunks. Larger chunks than will come from corn stover (almost power).
Charcoal from wood will leave chunks that will take centuries to break down, which is why it is not nearly as suitable for the creation of these soils unless they are finely crushed. Plant waste such as stover is already finely divided after charring and is easily incorporated into the soils which have been shown to hold several per cent of carbon.
#5? Do you have SEM micrograph pictures of pyrolized corn pollen (charcoal made from pollen) ? What pollen do you mean? Where is the pollen from? How can the species of the pollen be determined when it is charcoal? Are there other "cell structures" of corn or cassav present in the charcoal?
It was reported that corn and cassava pollen was the main pollen group in these soils. This would be independent of the char. The one thing archeologists can determine with a high degree of certainty is the nature of the crops grown on a site.
I don't have a problem with the possibility of using corn stover or cassava cultivars as feedstock for the production of charcoal. I just do no see the evidence that this was the primary feedstock for the production of charcoal in the Amazon from 4500 to 500 years ago. So far, you are telling a story, but have presented nothing scientific to back up your assertions. Do you have any published scientific papers supporting your claims? I have not heard any of this before or read any of it.
This is my hypothesis drawn from available evidence and a solid grasp of the constraints visited upon a primitive farmer. Actual confirmation came from the pollen profile, rather than the other way around.
Get Johannes Lehman's (from Cornell) book. Its $229, but it is the best reference on the original "Terra Preta" formations found in the Amazon rainforest. Also, Christoph Steiner has actually been in Brazil, studying the development and use of "Terra Preta" soils. He is very familiar with trying to grow corn in the native soils.
The amount of land found covered in "Terra Preta" soils is claimed to be about "the size of France". If there was enough corn and cassava to pyrolyze into charcoal and put into that soil, then where is all of the corn now? What about the cassava? Neither is there in the Amazon rainforest now, enough to produce that much charcoal.
Corn and cassava are human crops that require human intervention. The humans died off shortly after the new world was first discovered.
I do not know the age of the Amazon rainforest? But, I would venture that it is greater than 500 years old. Brazil has certainly been near the Equator for more than 500 years. The Equatorial regions of the planet Earth are ubiquitous with tropical rainforest. Corn fields are rare and always manmade. The nature of that climate zone and the soil there does not support corn. Why isn't there charcoal made from corn in North America? There is and was more corn in North America than there is or was in South America.
That is a very good question. Why was the technique not applied throughout the Mississippi valley and Mexico? My first conjecture is that it simply turned out to be largely unnecessary in these soils and field rotation remained a viable option. Of course, the knowledge may simply have never spread from its homeland. It is a long way without a good intermediary user.
I'm sure that the inventors of terra preta used mud to cover up their fallen trees and brush to make charcoal! It's still made that way in many places around the world. In fact that would largely solve the matter of how they mixed the topsoil and charcoal, because they are both right there together. In contrast, how much effort is it to work all that land every single year - six inches deep - to mix in a few pounds of corn stover charcoal for a culture that didn't even have one single draft animal for cultivation?? It doesn't seem feasible. It makes much more sense to do it all in one shot, considering the amount of work required to mix the two.
The difference with corn is that you have ten to twenty tons of material at hand in a one acre field. And it can be pulled by hand. No other major crop presents this combination. The charring process as I described earlier will naturally mix the produced biochar with at least an equal amount of earth. This can then be carried by basket to the seed hills and either dug into the hill – unlikely – or simply top dressed on the hill.
What we have is a protocol that a stick farmer can use crop after crop with a minimum adjustment in human effort that also maintains his fertility decade after decade. You simply go from pulling the stalks and burning them to actually using them to build an earth surfaced biochar stack.
But how did all this get started? I'll speculate that they learned about it by accident. Perhaps an understanding of it grew out of their firing of pottery and the disposal of the wastes? From the photos I've seen of some terra preta soil profiles, they made lots of
it. Maybe the quality of their clay was poorer than elsewhere and they had to make it more often and thus...??
I simply think that the nature of the corn root gave someone the idea to build a stack as I described that on burning created a lot of biochar which naturally was distributed to the nearby hills. This happened on a rapidly depleting field and postponed locally the abandonment of that part of the field. Once the connection was made, it became fundamental to that society and led to its huge expansion.
Whatever a month or so ago, Saibhaskar Nakka wrote about the terra preta 'signatures' he was finding in India - areas associated with the potter's work. Maybe there lies the answer? Baking of clay within semi-airtight containment, results in a mixture of ash and charcoal. And these wastes were then used by the potters for their fields. Maybe this was the way it all started in the Amazon?
To my mind, the real mystery of terra preta might not be so much how the Amerindians discovered how to use charcoal as a soil amendment, but why no other culture did!
No other culture had a crop like corn which produced ten tons per acre of dry waste that was actually in a packable form. Every other high volume waste is typically brush-like and it cannot be packed by hand enough to make it work well.