Very old farming techniques almost always carry old wisdoms.So, it is foolish to think that agricultural improvements move in a straight line: no matter whether it is closed-loop farming or, as a new study shows, a 700-year-old soil enrichment method!
Although it may appear illogical, but tropical forest soils are generally horrible for modern farming. This fact is due mostly to the insanely-dense amount of verve in these environments.
In contrast, in forests with lesser degree of lifecycles, dead plant and animal remains have time to decompose and release its nutrients into the soil. In the tropical forests, an immense number of insects, fungi, and bacteria speedily devour any decomposing matter before it has a sporting chance to enrich the soil with nutrients.
Rainforests like the Amazon basin, above ground, flourish as biological hot spots with exuberant growth and a riot of plant and animal species. Unfortunately, the red and yellow soils below are particularly poor in nutrients and organic matter. Once the lush vegetation is cleared, the heavy rains and tropical sun quickly decompose even that small reservoir.
Exception to this are the numerous patches dotted along the Amazon River and its tributaries, where dark, friable soil extends meters deep, fertile in nutrients and organic material. On the whole, an area [the size of France territory] may be covered by this Indian black earth, called terra preta in Portuguese.
“The textbooks say it shouldn’t be there. That’s justification enough for me to explore why it is there,” says Johannes Lehmann, a Cornell University professor specializing in the chemistry and geology of soils. Lehmann is one of a small-band of examiners in the U.S., Europe and Brazil who are deciphering the mysteries of terra preta after the phenomenon was “discovered” for the 3rd time ten years ago.
At a major scientific meeting, they explained that the black earth of the Amazon is exciting for widely disparate scientific reasons:
- Archaeology and anthropology. Terra preta typically is packed-full of shards of sophisticated pottery discarded as much as 2,000 years ago by an advanced civilization whose existence wasn’t even supposed.
- Sustainable agriculture. Unlike the typical rainforest soils, the black earth can be worked on for years, with minimal fertilization. Yet, it is essentially man-made, created by community activities that could be reproduced today by industrial means.
- Climate change. The key step in producing terra preta traps large amounts of carbon in the soil, avoiding the release of carbon dioxide, the leading greenhouse gas from human activities. Moreover, lab tests demonstrate that black earth also gives off less than regular soils of two other atmospheric bad actors: nitrous and oxide methane.
So, the crucial step is a method of weed control and land clearing called cool burning or slash-and-char, to distinguish it from slash-and-burn, widely used in tropical regions and widely condemned.
Indeed, in slash-and-burn, dry brush and grass are burned in open fires, spewing vast quantities of carbon dioxide into the atmosphere and leaving only small amounts of nutrients in the ash that’s then dug into the ground.
By comparison, slash-and-char involves burning wet vegetation so that it smolders underneath a layer of dirt and straw. Being robbed of oxygen, the fire only partly burns any wood or stalks, leaving most as tiny chunks of charcoal. This bio-char is turned into the soil.
Mr. Johannes Lehmann told a news conference at the annual meeting of the American Association for the Advancement of Science that only tiny 7 % of the carbon content of vegetation gets transferred into the soil by the slash-and-burn approach. On the contrary, the slash-and-char approach transfers almost half the carbon and most of the nutrients like phosphorus and nitrogen.
Why people living on hills overlooking many rivers in Brazil 2 millennia ago devised this approach is still a subject of argument, as is how they added all the extra organic content and ensured the soil was teeming with other micro-organisms and beneficial bugs.
However, multitudes of people around the world still live right in the tropical forests, so they had to examine the old way to make the soil actually productive for their sustained survival as well – the effects of the destruction of these forests on the eco-system excluding.
So, they have started using the same method that, for hundreds of years, rainforest farmers have used to enrich soil with biochar that is charcoal. They continue to use one of the oldest techniques already mentioned above – the black earth or terra preta technique.
Wet vegetation is burned, producing little bits of charcoal, which are ground into the soil. Eventually, this creates an incredibly rich, fertile soil for many abundant crops.
Researchers at universities around the world have realized that the oldest Amazonian farming technique is replicated in various forms around the world, including West Africa, in only the past few years!
The new study, led by researchers at the University of Sussex, analyzed 177 sites in Liberia and Ghana and proved that biochar additions, employed for centuries in these areas, have increased the carbon levels in the soil by 2-3 times.
By living in villages in these countries, researchers described the techniques: ash and bones, along with kitchen waste, are recycled back into the soil. The press release for the study says the practice could help alleviate climate change problems. What they mean by that is that the biochar method transfers carbon to the soil, reducing the amount of carbon dioxide released into the atmosphere.
Yet, this depends on the specific method: The infamous slash-and-burn method, in which material like trees and plants are simply burned in open fires, transfers a very small percentage of carbon to the soil, spreading much of it into the atmosphere in the form of harmful carbon dioxide.
But slash-and-char, in which wet vegetation under a layer of straw is burned into charcoal, is much more efficient since it transfers almost half of its carbon content into the soil!
You might notice that both slash-and-burn and slash-and-char include the word ‘slash’ and involve deforestation, one of the most destructive acts for the environment. The carbon sequestration that results from slash-and-char makes it the lesser of 2 evils, but yet not good enough.
It is obvious that there are sustainable sources of biochar that can be used by a home gardener. If you want to use the technique without burning down the woods in back of your house, check out this Washington State University guide for more guidance.
American Association for the Advancement of Science
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