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Bio-Char: What is it and why is it important?


Who can benefit from Bio-Char?

Forest Gardens, Urban Gardens, Bio-Intensive Gardens, Orchards, Dairy Farms and many more – all can benefit from more carbon in their soil!!

In the current state our planet we are losing approx. 9 kg of top soil for every 1 kg of vegetables in the supermarket! Drought is a concept we hear about too often in NZ (and not because of less rain, but because of the lack of carbon that we have created in the soil)! Our water ways are being polluted with the chemical fertilisers that we are needing to pour more and more of (again, because of the lack of carbon to hold the minerals in the soil)!

In this state, every action that has anything to do with the soil – has to be incorporated with increasing the carbon!

Bio-Char is one of the key techniques that now many around the world are researching and experimenting with, although it is not new!

It seems that people, for many thousands of years, have been using Bio-Char as one of the key elements in creating the ‘Terra Preta’ or ‘Black Earth’ found in the Amazon basin, and made it to be as fertile as we can find it today.

A simplified explanation:

On our miraculous planet, exists a fine equilibrium between organisms that are in the process of photosynthesis and use the energy of the sun in order to convert CO2 (Carbon Dioxide) from the air, to oxygen (O2) that is released back to the air, and carbon that is incorporated into their bodies or passed on to the soil in various ways – these are most plants.

On the other side of the equilibrium are most other living organisms, or ‘breathing’ organisms, those breath-in oxygen and breath-out that oxygen after it had been combined with carbon from their bodies.

As well, humans have found faster ways to release that carbon back to the atmosphere, while making use of the energy- fire, or burn.

The consequences of breaking this equilibrium have been talked about enough… although understanding how slow the process of putting carbon in the soil (not faster than a growing plant) and how fast is the process of releasing it back to the air (as quick as that same plant burns) is critical!

When we realise how every bit of energy released from fuels on our planet is originally solar energy, stored in our environment in different ways (wood, coal, char, petroleum) and we look at how much energy is being used daily and how much is falling on earth in the shape of light, it is easy to see that this equilibrium is being broken…

Char, or charcoal, is organic matter, put in high temperature for a period of time, with no oxygen.

The triangle of fire (of which we wish to avoid) is: Fuel, Heat, Oxygen.

When we put those 3 together we get fire, for example: with some fuel like a forest / a piece of wood or a sheet of paper with enough heat from the sun or a lighter plus the oxygen that is available in the air, we get fires.

During the process of burning, carbon molecules (which are a main ingredient of which most fuel is made of) are combining with the oxygen in the air, creating CO/CO2 molecules which is a gas released to the air.

When we put a piece of wood in the fire any moisture is being heated, and released, the material is getting hotter and hotter, other gases and tars are being released (burned or not), the heat is breaking the woods’ structure, oxygen is combined with carbon (and released to the atmosphere as CO2) and some molecules are left as ashes (calcium, potassium, phosphate, and many more…)

Making char is a very similar process, the only difference is that excluding oxygen from the process means that the carbon is staying with the woods’ structure (as it can’t combine with oxygen). We still burn the tars and other gases – so we still have a fire, only that we’re not releasing the carbon! We get energy while releasing much less carbon into the atmosphere!

The molecular structure of char is one of a vast amount of surface area, it can hold as much as four times its weight in water, it can keep large amounts of oxygen in it and it can be a more stable carbon than humus – it will last longer in the soil, the result of that is a fast, low cost, long term structure for holding moisture, minerals, and microorganisms. All are key for building soil.

There are many ways to make char, using TLUD- top lit up draft burners, retorts of many sorts and more, I’ll focus on one way which is somewhat different.

For a while, we have been making biochar using TLUDs and Retorts, experimenting with different fuels, and techniques. Sense we have a lot of large size or odd shape prunings (coming to us in large quantities from feeding the urban garden rabbits with Tagasaste branches and from our forest gardens) I’ve been looking for a simple, low tech, versatile and time/ energy efficient way to char those. I looked a bit into traditional charcoal making in a pit – that seemed like an amazing way to make char, though is very skilled (of which I have no experience with yet) and at second look seems somewhat polluting, as much of the tars/ gases are left un burned, as well the temperatures are usually low which results in low quality char. While researching I have found the work of ‘Ithaka Institute’ in Switzerland –, Hans-Peter Schmidt, has done some amazing research, and put together the kiln he is calling ‘Kon-Tiki’- simple, easy to build, can make all sorts of gnarly wood into char without processing, is clean burning, easy to operate and makes high quality char, seemed to be exactly what i was looking for! So quickly found a way to make one and try it!


The main idea is to burn wood in the kiln in a way that makes the fire protect the char from oxygen.

When we burn wood in an open fire we can observe how as we add wood, first the fire is burning on top and above the wood – burning the tars and gases, only after those are consumed the heat and the oxygen increase around the wood and carbon is being released as CO2, at that point we can observe white patches (ash) starting to appear on the wood.

If burning wood in the kon-tiki we add layer after layer of wood, each layer we put in the heat releases its gases (which are being burned in the fire and releasing more heat) at the point that the wood is starting to ash, we add another layer of wood, the top layer is now in the heat, releasing its gases and consuming the oxygen above the top layer – protecting the previous layer from oxygen – keeping the char intact.

As we add more and more layers, the structure breaks, and the char takes less and less space, until the whole cone is filled with char and there is no more space to add wood on top of the fire, we stop the process with pouring water into the kiln (or from a bottom attachment which allows us to start filling the kiln with water while still burning at the top and create more even char while releasing less pollutants at the end) the bigger the kiln the bigger the amount of char per batch.

In the first burn it took us 3 hrs – from starting to collect the wood bringing it next to the kiln, to having 300 Litters (volume) of char. If you tried making char before you’ll know that this is very good for any back yard operation.

We can add to the kiln thin or thick pieces of wood (as long as similar within each layer), we can up-scale or down-scale the size of the kiln to our need, and it is made out of materials that will last for years.

The next stage is to put it on big wheels, attach a long handle, and we will be able to take it to a walk around the village, and make char where its needed, or where the fuel is being piled. Add a rim around the kiln so that the air being burned in the kiln is pre-heated by the outside of the kiln – which will result in hotter cleaner burn and better char, and a way to heat large amounts of water using the heat releaset at the top.

If you are making your own just make sure that the walls are in 65 degrees from the ground and the opening at the top is at least 1 meter wide.


Warning! – do not add the raw char to your garden!
It will take time and minerals until the char is saturated and makes the minerals available to your plants.

To charge and inoculate your char add it to your compost piles, put it into your composting toilets, add it to your worm farms or black soldier flies farms, soak it in urine, or don’t charge it, and use it as a water filter, as an insulation material, as animal supplement, or many more…

Biochar4.1– Written by Shaked From

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