Could there be a new day for this old technology?

by Andy Balestracci


Floating downstream into his own heart of darkness in June 1542, Francisco de Orellana had no idea what to expect. What we do know of his murderous journey, as he sought the fabled golden kingdom of El Dorado, is gleaned from a written chronicle of the Spaniard’s observations. His writings paint a landscape populated with bustling villages and even a few cities along the banks of the river. Local men and women justifiably fought Orellana and his soldiers of fortune to protect their homeland, although it was the women archers that eventually gave this area and the river its name: The Amazon.

Like the Greek historian Herodotus’s accounts of Scythian women warriors on horseback, tales of a heavily populated Amazon were relegated for hundreds of years to the realm of a good yarn. Amazingly, and with the help of archaeologists over the last few decades, this depiction of a dense and thriving society along the Amazon has shifted from fable to fact.

Prior to the work of these archeologists, the predominant post-European conquest view of the Amazon depicted untouched expanses of forest, sparsely populated by semi-nomadic hunter-gatherers. Poor, acidic soils throughout the region were thought to limit both quantity and variety of crops. Heavy precipitation and tropical humidity allowed for the rampant growth we picture when imaging the rainforest, but that biomass, and the limited fertility from its inevitable decay, exists in a fragile skin over the land. Rainfall both gives life and depletes it by washing soil downstream.

With the advent of satellite imagery and LIDAR, which uses pulses of laser light that can penetrate through gaps in the forest canopy, we now have detailed maps of the topography underneath the trees. With the help of follow-up ground examinations by geographers and archaeologists, we can now see large scale earthworks and terraces that point to sizeable former settlements that could have only been made by large populations of workers and farmers.

The discovery of these sites and the implications for the area’s past civilization are stunning. Though greatly diminished by pandemics of European disease and genocide, clearly at one point the Amazonian people had the agricultural resources and know-how to support a much larger population than originally thought.

Associated with these sites are soils that are dark and richly fertile even after many hundreds of years of abandonment— uncharacteristic for the lower Amazonian watershed. These dark soils, locally called terra preta, are definitively anthropogenic (human made) in origin, with bits of ceramic, bone and, most importantly, charcoal contained within.

According to researchers, this charcoal is the magic ingredient that can transform a thin layer of easily depleted topsoil into robust and enduring farm dirt. Outside of the Amazon, this carefully rendered charcoal is known as Biochar.


Biochar is not your garden variety charcoal—it has to be made within specific parameters. You can burn any dry vegetable or animal biomass in a low oxygen environment, in a process called pyrolysis. During pyrolysis, the lack of oxygen causes the material to break down chemically, burning off gases and leaving a carbon-rich charcoal. Since charcoal is highly porous, it contains an astoundingly large surface area for its volume. It is estimated that a single teaspoon contains as much surface area as a football field, or 1.32 acres. Combine this with the fact that carbon is highly adsorbtive and binds with any atoms in its vicinity. This is bad news if you add raw biochar directly to your farm or garden soil, as it will rob nutrients from plants and microorganisms. It’s great news if you first combine it with compost or compost teas, as it locks in the available nutrients for future use.

And here we return back to the example of terra preta soils that are still fertile, nutrient-dense and biologically diverse after centuries. If you have ever seen the diversity of life in and around a coral reef, you know that it’s in large part due to its complex, multi-layered structure. Just as a coral reef provides habitat for a diversity of species underwater, biochar acts like a land reef for a plethora of fungi, beneficial microbes, and nutrients. Because biochar resists decay, it could transform annually produced biomass into a substance that captures carbon and carbon dioxide, locking them into soils rather than releasing them into the atmosphere through decay, thereby reducing global warming.

The easiest way to make biochar is to adjust how you approach your winter burn pile. First get your hands on a county burn permit and confirm it’s a county prescribed burn day. You can use fruit tree or vineyard prunings, grape pomace, manure or forest thinning material from your property.

Next light your dry burn pile from the top and allow it to burn downwards. This method, known as a conservation burn, creates the low oxygen pyrolysis burn, much like a match burning from the top down—cleanly, with little or no smoke. Your neighbors will thank you for the smokeless burnpile, and it’s good for the planet. Once the pile is reduced to glowing coals, extinguish with water. You now have raw biochar! The double benefits of sequestering carbon and creating long-lasting, healthy soils could contribute to the survival of our farms and future local food security.

Biochar Compost/Manure mix

To any compost or manure pile add no more than 10% Biochar by volume. Adding biochar will reduce smell, prevent nutrient leeching and runoff, greatly enhance long term fertility.

Biochar Tea Recipe


  • 5 gallon bucket of new Biochar/charcoal
  • 10:1 Water-Compost tea/Worm Compost tea

Add together. Let soak for 1-2 weeks. Mix into garden soil at a rate no more than 10% Biochar to soil.


Andy Balestracci is a writer, gardener, and homesteader living in Boonville. He owns the heirloom seed company, Diaspora Seeds.