by Nicholas Chambers
In 1542 the Spanish conquistador Francisco de Orellana sailed down the Amazon River to its mouth with the Atlantic Ocean. In what has been termed an improbable voyage, reports describe densely populated settlements running for hundreds of kilometers along the river’s edge, suggesting much higher population densities than have been there since. Due to the subsequent demise of these cultures from cultural uprooting and disease epidemics brought about because of the Spaniards, the heirs of these cultures are no longer as populated nor as settled as they were before Contact. What they did leave behind, however, is a legacy of highly productive organic agriculture, and extremely dark and rich soils that have come to be called Terra Preta de Indio or Amazonian Dark Earth (ADE).
The “terra preta” (dark soils in Portuguese) soils of the Amazonian Basin are more than just black and fertile. They are extremely high in available minerals and nutrients and retain moisture like a sponge. Their ability to promote the spread of mycorrhizal fungi, that web-like immune system of healthy soils and forests, contributes to it becoming firmly established and long lasting. It can be up to 6 feet deep and possess the intriguing ability to regenerate at the rate of 1 centimeter per year. Agricultural crops planted in this soil can yield four times the harvest as compared to nearby fertilized “terra comum” (common soils).
The secret of this soil is that it is anthropogenic in nature. It contains ash residue, pottery shards, fish and animal bones, and the composted remains of plant residues, kitchen scraps, and human and animal feces. The one remarkable constituent is charcoal, black carbon, or what has been recently realized with the name, biochar.
Whether these pre-Columbian Amazonian natives were practicing a deliberate soil management practice, or were just “throwing away” their organic by-products, is a matter of the chicken and egg. The fact that some of these terra pretta soils are up to 2500 years old, though, suggest these “primitive” farmers were indeed practicing a soil sustenance regime that could support dense settlements over thousands of years. Positive feedback loops promote enduring legacies.
While the remains from cooking fires of ash and charcoal were definitely spread over food-producing soils, there are “slash and char” practices in the Amazon that are still being done to this day. This is compared to the “slash and burn” practices that only yield tremendous carbon dioxide (CO2) emissions and very thin and fragile soils. Slash and char practices utilize earthen kilns to fire the woody biomass of the felled timber in an oxygen deprived pyrolysis. The product of this is charcoal, or biochar, and the gaseous emissions including carbon monoxide (CO), hydrogen (H2), methane (CH4) and still some CO2, among others. Most of the carbon that was absorbed from the atmosphere as CO2 during the photosynthesis of those trees is retained in the biochar as carbon. Then, as this biochar is added to soils it becomes a carbon sink that remains there for thousands of years. As it contributes to engendering increased plant growth, even more CO2 is absorbed from the atmosphere resulting in huge carbon sequestration potential. Since it is not consumed within the soil it acts as a long lasting catalyst for optimal chemical, physical, and biological processes.
Researchers at Cornell University have described biochar soils to have “the potential to revolutionize the concepts of soil management.” Having both this affinity for nutrients plus its long stability could be invaluable to address the problems such as soil degradation and food security, water pollution from agro-chemicals, and climate change. In essence: “Soils with biochar addition are typically more fertile, produce more, and better crops for a longer period of time.” Char additions of 4 to 20 tons, sometimes 160 tons, per acre have been reported to yield up to three to four times the yield in crops.
This is also good news for the numerous nascent biomass gasification technologies around the world, along with the many that are already well established. They are realizing the by-product of their low temperature pyrolysis, the biochar, is a potential way to theoretically have a carbon-negative biofuel.
Biomass gasification is already a carbon-neutral renewable energy process. This means no more CO2 is released in the process of capturing energy than was absorbed during the prior biomass life cycle. Adding the char to soils banks up to half of the original feedstock carbon as a solid soil catalyst and prevents it from becoming a greenhouse gas. Biomass gasification already has many potential derivatives such as electricity, hot water, and liquid fuels, and now it has the ability to fix carbon, contribute to sustainable agriculture, and promote soil remediation.
In Colorado, eleven out of the twenty-two rural electric co-ops lie within regions severely affected by the current and massive beattle-kill epidemic. Reducing this tremendous wildfire hazard by removing the substantial timber resources, creating value-added wood products, and generating negative-carbon electricity with the by-products could prove to be a productive management solution. The ability to then return at least some of the resulting biochar to the forest soils could promote healthy new stands of resilient timber and undergrowth.
As was the case with many early European penetrations into the interior of the Americas, Conquistador Orellana witnessed the intact and huge populations of indigenous people that were present before European diseases took their toll. These people relied on highly-productive agricultural practices, like the chinampas or floating gardens of the Aztecs, which are now demanding the attention of modern researchers and agriculturalists. They are finding the legacies of these ancient civilizations had practices that are out-performing some of the developed world’s notions of agricultural productivity, such as the alleged “green revolution” of synthetic pesticides and fertilizers. It turns out what is the newest is not necessarily the most productive.
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