Modern-day Biochar by John Hermans *

John raking up the end product beside his ‘biochar producer’. Nice t-shirt too!

Biochar use has been documented as far back as the Amazonian Indians, who created tera preta or ‘black earth’. These nutrient-enriched soils retain much of their higher fertility, and their char, thousands of years after they were created. Biochar can also permanently lock up carbon to help neutralize our carbon footprint. In this world where governments are largely failing to mitigate a climate catastrophe, this is another path for a ‘bottom-up’ global effort.

Biochar is now commercially available as a soil conditioner, at around $10/kg, but if you are not confined by allotment size, it is quite easy and cheap to make instead. You can also then control what goes into it. In my case, I have been using the sticks and leaves that I would otherwise have burnt to reduce summer bushfire risk.

Making it has also given our household another option for becoming truly carbon neutral, other than planting trees. Biochar means we can now lock up atmospheric carbon in the soil, potentially for thousands of years, rather than have it re-enter the atmosphere when the ground litter rots or is burnt. Once it is added to the soil, it remains mostly inert to oxidation and hence does not re-enter the carbon cycle. At the same time, it increases the soil fertility in our extensive food garden.

When organic matter is burnt in the open air, it nearly all burns to ash, with only very small amounts of unburnt black char. In biochar manufacture it is preferable to use enclosed steel drums to control oxygen delivery. When the fuel is burnt in controlled conditions, gas is converted to CO2. An added advantage is that it is a fairly smoke-free production process— far more neighbour-friendly than open-air fuel reduction burning. But because so many people use this method and will continue to do so, I have describe an option that has little added effort to this procedure.

There are many ways that char is produced commercially or in back yards. A method which I have recently developed allows char to be made from leaves and small sticks that are routinely racked up from under Eucalyptus trees in the spring and summer period. By using a modified rake with the lower section of the handle being made of steel, to avoid being burnt, there is little else required to achieve the task.

A long row of leaves and sticks around a meter wide and 20 cm high is created with a simple leaf rake, and around 6 meters long, the up wind edge is set alight, it is helpful to use an accelerant such as kerosene, to get it all going at once. When the leaves are mostly all alight, you then use the extended handle rake and roll the leaves from below the row over top of the burning leaves, continue doing this for as long and as quickly as you can, and before you know it the flames go out and you are left with nothing but small leaf sized of biochar! This season I ended up with two 200L drums of char using this method.

Reduce atmospheric CO2, reduce wild fire fuel loads, and increase your garden soil nutrition capacity. Happy biochar making!

* an edited version of an article by John that appeared in Renew 124