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The Secret Of El Dorado


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Anyone else see this ABC documentary. I had to do a search on it. A remarkable way of maintaing soils with the aid of charcoal has been rediscovered and is believed to be the secret behind an ancient Amazonian civilisation which thrived until New World diseases were introduced and ravaged the population.


EXTRACTS follow.




BBC2 19dec02

Programme Summary

Transcript (below)


In 1542, the Spanish Conquistador, Francisco de Orellana ventured along the Rio Negro, one of the Amazon Basin's great rivers. Hunting a hidden city of gold, his expedition found a network of farms, villages and even huge walled cities. At least that is what he told an eager audience on his return to Spain.


As productive as the rainforest may appear, the soil it stands in is unsuited to farming. It is established belief that all early civilisations have agriculture at their hearts. Any major population centre will have connections with a system of intensive agriculture. If a soil cannot support crops sufficient to feed a large number of people, then that serves as an effective cap on the population in that area. Even modern chemicals and techniques have failed to generate significant food from Amazonian soil in a sustainable way . The thought that indigenous people could have survived in any number - let alone prospered - was dismissed by most scientists. Scientific consensus was sure that the original Amazonians lived in small semi-nomadic bands and that Orellana must have lied.


Bolivia's Llanos de Mojos (Mojos Plains) are 2,000km from Orellana's route down the main channel of the Amazon. The terrain is savannah grassland with extreme seasons - floods in the wet; fires in the dry. Crops are hard to grow and few people live there. But back in the 1960s archaeologist Bill Denevan noted that the landscape was crossed with unnaturally straight lines. Large areas were also covered with striped patterns.




Recently, Denevan's work has been followed up by Clark Erickson, a landscape archaeologist. His attention was drawn to the numerous forest islands dotted across the savannah like oases. Down on the ground he found them littered with prehistoric pot sherds, a clear sign of early human habitation. Some mounds were as much as 18m high and much of the pottery was on a grand scale as well. Such huge vessels were too big for wandering nomads. Here were permanent settlements, where hundreds or even thousands of people had once gathered for huge ceremonies. To Erickson, these were signs of an advanced society - a civilisation.


"Their work is on a par with anything the Egyptians did"

Dr Clark Erickson, University of Pennsylvania Museum


Denevan and Erickson have shown that the striped patterns are relics of a system of raised fields. From the air, the area which appears to have been turned over to such agriculture is clear. It covers thousands of square kilometres. In conjunction with the controlled irrigation a canal network might offer, it could have sustained hundreds of thousands of people. Erickson believes the Mojos Plains were home to a society which had totally mastered its environment.



The secret of the soil.


The Indians may have used a 'slash and char' technique.


Soil scientists analysing the terra preta soil have found its characteristics astonishing, especially its ability to maintain nutrient levels over hundreds of years. 20th century techniques of farming on cleared, torched rainforest - so-called slash and burn agriculture - have never been sustainable. With the vegetation burned off, the high rainfall soon leaches all the nutrients out of the soil. Research has shown that even chemical fertilisers cannot maintain crop yields into a third consecutive growing season, yet terra preta remains fertile year after year.


"The material is alive. The biology is the important thing"

Prof William I Woods, Southern Illinois University Nature and nurture.


Again, Orellana's accounts offer potential insight. He reported that the indigenous people used fire to clear their fields. Bruno Glaser, from the University of Bayreuth, has found that terra preta is rich in charcoal, incompletely burnt wood. He believes it acts to hold the nutrients in the soil and sustain its fertility from year to year. This is the great secret of the early Amazonians: how to nurture the soil towards lasting productivity. In experimental plots, adding a combination of charcoal and fertiliser into the rainforest soil boosted yields by 880% compared with fertiliser alone.


Yet terra preta may have a still more remarkable ability. Almost as if alive, it appears to reproduce. Bill Woods has met local farmers who mine the soil commercially. They find that, as long as 20cm of terra preta is left undisturbed, the bed will regenerate over a period of about 20 years. He suspects that a combination of bacteria and fungi is causing this effect.


Today, scientists are busy searching for the biological cocktail that makes barren earth productive. If they can succeed in recreating the Amerindians' terra preta, then a legacy more precious than the gold the Conquistadors sought could spare the rainforest from destruction and help feed people across the developing world.




Not to mention growing filthy buds year after year!



I saw the experimental plots and the yield from charcoal imbedded soils combined with fertiliser was staggering. The other plots were useless within 2 years but the terra petra grown crops were huge. This would be great to try in Australia.


It looks as if charcoal in and of itself is good for the soil. So nect time you have to do some back burning scrape up some of that half charred vegetation and use it on your veggie patch.


Slash-and-char: a feasible alternative for soil fertility.

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