History of Biochar
We all know what charcoal is, having used, or seen it, in a BBQ, but many of us will not have come across the term biochar. These substances are almost the same thing, but with one important difference: biochar is exposed to more oxygen when it is being produced. This has the effect of burning out some of the more volatile compounds within the original structure. The charcoal we burn on our BBQs is much denser and burns hotter and slower. Biochar on the other hand has a sponge like structure which makes it brittle. It will still burn, but does so far more quickly, which is not ideal for BBQs.
Mother Nature has been producing charcoal and biochar since vegetation first appeared on earth. Both are produced in every forest fire. Crudely speaking, as vegetation burns, it first transitions to charcoal, then to biochar and finally to ash. We have all seen images of the charred stumps and branches of trees after a fire has passed through. This black residue is carbon-rich charcoal, (biochar) which was unable to maintain sufficient heat to continue burning. Forest charcoal and biochar will gradually break apart (but not break down) and mix with the surrounding soil. Here it will remain for centuries. Eventually, much of it ends up in the sea or in swamps such as the Everglades, as a result of natural soil erosion. Before that, the biochar element will have enriched the soils it mixed with along the way.
We think of carbon sequestration as something mankind has come up with to combat climate change, but Nature has been doing it since the beginning of time. A forest fire releases huge amounts of carbon into the atmosphere as carbon dioxide, but, assuming the forest completely regrows, more carbon will be captured than was originally released. That’s because some of the forest’s original carbon load wasn’t released into the atmosphere as carbon dioxide: it remained locked in charcoal and biochar. Plants extract carbon from the atmosphere in order to grow. When they die, that carbon is eventually released back into the atmosphere. In this way, carbon shuttles back and forth without loss or gain. However, if some of that carbon is trapped in charcoal and biochar, thus prevented from returning to the atmosphere, then the net effect is less carbon dioxide.
Some forests and savanna lands burn naturally on a fairly regular basis. Their soils are continuously being topped up with natural biochar, which increases fertility. However, other environments, such as rain-forest, hardly ever burn naturally, so receive very little, if any, biochar. As you will learn in the section on ‘using your biochar’, biochar is Nature’s storage facility for plant nutrients and beneficial microbes. Soils that cannot hold onto nutrients and moisture have very low residual fertility. This is the case in most rain-forests. To combat this, rain-forest ecosystems are very efficient at recycling. A leaf that falls to the forest floor is rapidly devoured. Although the nutrients which the leaf contained will gradually pass into the soil via animal dung or decomposing micro-organisms, they won’t stay there for long. The forest flora is adept at catching nutrients and transporting them back to the canopy. The net result is that virtually nothing of much value remains in the soil.
This fact became apparent to early humans who cleared rain-forest to plant crops. Those crops soon used up any nutrients left behind after clearing, so one or two crop cycles was all the land could sustain. The earth then became rock like or ‘laterized’. Early farmers understood that adding manure and organic matter aided crop growth, but any precious nutrients the farmers added soon leached away. Farming was revolutionised by the discovery that adding biochar to organic fertilisers would help the soil retain nutrients and moisture. The same land could then be cultivated year after year.
Most of us think of the Amazon rain-forest as an ecosystem that has remained untouched for millennia. We now know that large areas of this pristine forest were once intensively cultivated by humans – some 150,000 square kilometres. We know this by what has been found below ground, rather than above; namely a thick layer of dark, carbon-rich fertile soil known as black earth, terra preta in Portuguese. It could only have got there through decades of farming with biochar.
Setting out in 1541, Explorer Francisco de Orellana travelled through the Amazon basin in search of the fabled city of El Dorado. He wrote of densely populated regions stretching hundreds of miles along the Amazon River. He passed through large cities with well-established infrastructure and surrounding farm land. It is arguable that this extensive civilisation was only possible because of biochar.
What happened? The Spaniards brought with them deadly diseases, such as small pox, against which the native Amazonian populations had no immunity. The entire civilisation, along with their farming practices, collapsed. Nature returned the farmlands to forest.
‘Terra preta’ is not unique to the Amazon. Ancient deposits of biochar-rich soils have also been found in equatorial Africa.
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