Hooray for the Ancient Amazon Farmers

Keywords: Indians; Amazon; rainforest; Orellana, terra preta; black soil; archaeologists; slash-and-burn

Everyone is dismayed because the Indians living in the Central Amazon have been burning huge tracts of rainforest every year – but there’s astonishing new reason for hope. To explain, I have to go back 9,000 years to the time when there was an extensive civilization in South America.

Archaeologists have assumed that there could not have been a real civilization in that area, contrary to the reports of one early explorer named Orellana, who in 1542 had led an expedition searching for El Dorado, the kingdom of gold that supposedly lay hidden in the jungle. He found no gold, but towns that stretched as far as 15 miles. There were many roads and highways, and some very large cities. The land was as fertile as in Spain.

A few years later, Spaniards returned to the Amazon, but found nothing resembling the civilization that Orellana had reported. In retrospect it seems likely that the first explorers had imported their diseases, which swept through the Indian populations, killing almost everyone. Only lately have the traces of roads and raised fields been discovered.

The present Indian population practices slash-and-burn agriculture — not by choice but from necessity. The thin, yellow soil of the region is infertile, and the heavy rains wash away its nutrients, so that after a few years the farmers must move on, burn another part of the rain forest, and try to raise enough food in their new plots to feed their families. Archaeologists believed that no real civilization in that area had been possible, for only settled agriculture can support cities and large populations. They assumed that the current slash-and-burn system was all that had ever been possible.

But not so. In the Bolivian Amazon region, the land is a savannah, interspersed with “islands” of forest. When these forests were investigated, it became clear that they were places where people had lived in large numbers, for the soil was bursting with shards of pots, including huge vats that had been used to cook meals for hundreds of people. These archaeological sites were hundreds, even thousands, of years old. Moreover, there were stripes connecting them that could be seen from the air. These had been roads in ancient times.

Next the scientists explored the inland regions of the Brazilian Amazon, where they found large areas where the soil was remarkably different from the usual yellow dirt. As much as ten percent of the land is actually rich, dark soil called “terra preta.” As the photo shows, this soil is often two feet deep, and occasionally even two meters. It is full of pottery shards dating back possibly even 9,000 years, plus food scraps and other plants that had been used as much. This rich soil had been created intentionally by the inhabitants, and it remained rich throughout the whole period since then. It is so fertile that the owners today even mine it and sell it to other farmers. The dark color comes from the remarkable component that makes it so special: charcoal. The people did slash-and-burn, to be sure, but the way they burned the wood was special: call it "slash and char.” They built mounds around the logs so that they burned incompletely, creating charcoal, which they mixed into the soil. (Complete burning, on the other hand, reduces the plant material to ash, which can be swiftly washed away by rain.) Because the terra preta was so fertile, the ancient farmers did not have to move on and burn new patches of jungle, but could live in settled towns of large population size as long as 1,000 or even 3,000 years continuously. This discovery, if applied today, could confer the same blessings on contemporary farmers.

To explore this old technique, Christoph Steiner, of the University of Beyreuth, replicated the method experimentally, comparing it to current techniques. With the traditional slash-and-burn methods, there was nothing growing anymore after the first harvest. In another plot, he applied mineral fertilizer, but it too failed to produce enough grain to support a family. But where they applied additional charcoal, there was a big improvement, and when charcoal and mineral fertilizers were applied together, the crop was 880 percent higher then just the mineral fertilizer without charcoal. The charcoal seems to hold the nutrients in the soil.

There’s an even more astonishing discovery, too. In the areas where the owners are mining the ancient terra preta soil and selling to their neighbors, the old terra preta regenerates itself! A farmer digs into the soil but leaves 20 cm of it, which he allows to rest for about 20 years, with new vegetation falling on it. At the end of this time, the dark soil is the same as it was before the mining took place. Apparently there are some kinds of micro-organisms in the soil that allow the soil to grow. If this secret can be unlocked, scientists think the technique could be used all around the world, boosting food production. Not only would it bring slash-and-burn methods to an end, but it could help feed the world’s population, save the rain forest, and even help protect the earth’s climate, for terra preta is an excellent carbon sink, absorbing and holding carbon dioxide in the earth. To some extent this could compensate for the disastrous destruction of the rainforest.

That research is worth celebrating! Hooray for those brilliant ancient Amazon farmers – and for today’s archaeologists!