It all started when…

We came across a way to make reasonable quantities of biochar using resources we have to hand. We have been aware of biochar and the debate around its efficacy for some years. It was when we came across the Kon tiki kiln (pictured above) that we realised we could integrate biochar into the Carmyllie system.

Carmyllie produces huge quantities of woody biomass. A small amount of it ... we use to heat our house. Some more ... we sell as firewood. And the overwhelming majority of it remains in the environment and decays and returns to the soil from whence it came. In doing so it provides habitat for creatures small and smaller.

By transforming some of that woody biomass to charcoal we create a process that will lock up and amount of carbon for a very, very long time. While doing so, it changes the soil in ways that are not yet well understood. That said, the evidence is that biochar:

• acts as a long term carbon sink;

• improves soil structure and increases water retention;

• retains and replenishes soil nutrients;

• reduces nitrous oxide and methane emissions from soil;

• provides more secure habitat for micro-organisms and fungi; and

• acts as a pH buffer.

Our Kon tiki kiln takes about a tonne of woody biomass and produces 3 to 00 kgs of charcoal.

The system

The kiln was manufactured in Tasmania by Terra Preta Developments. It uses a particular conical shape to do what is necessary to produce charcoal (rather than ash) from the burning of woody biomass … that is it excludes (most) oxygen. Frank Strie (TPD owner) has come up with several innovations over the basic Kon tiki kiln concept. Three are critical to the effectiveness of our system:

• the kiln is mounted on a frame and can tilt. This makes it easy to unload the charcoal after a burn;

• the kiln has a system that delivers liquid to quench the burn from below. The same system also allows the quench water to be drained for use elsewhere; and

• the kiln has a heat shield made from stainless steel. It hangs about 10 cm out from the kiln and is very effective in shielding the operator from much of the radiant heat.

The next part of the system is woody biomass we collect. There is no lack of this at Carmyllie. We try to organise it so that the process of collecting serves at least two purposes. Most often it is is a ‘tidy up’ of some sort that is the ‘other purpose’ … a fallen limb, coppice prunings or slash needing to be moved.

Collecting firewood for sale or our own use produces heaps of material. The photo to the left shows us picking up firewood that has dried in the forest. It is collected using the firewood trailer built (to my design) by James Sciberras. The next photo below shows stacked firewood in the background. When the sticks are cut to (firewood) length, the short bits go for biochar. See the Firewood page.

The photos below shows slash jammed into our firewood frame for cutting up - and then stacked ready for use. The kiln works best with a mix of material size, but only up to about 10 - 15 cm diameter. Over that and we can get unburned bits left when we quench.

The stuff pictured goes … whoosh … and gets things started. We need bigger material later on in the burn. The next photo shows the variety of material that we collect for burning. Lately we have been recovering pine logs that were not taken in the latest pine harvest. The quantity of fibre that the forestry industry leaves behind on the forest floor … does not amuse me. It’s not even clear to me why they do it sometimes.

As the burn proceeds, we watch for signs of ash on the burning material. That is the signal to add more biomass - and to keep on doing so for 4 or 5 hours. By that time the kiln should be fairly full of charcoal. It is then time to quench …

Charcoal is not biochar. However it is extremely porous and has a huge surface are (300 m2 / gram). It also has cation exchange capacity (CEC) - that is an ability to bind positively charged ions to its surface and to make them available later to plants and microorganisms. Porosity and CEC are at the centre of biochar’s ability to positively affect soils.

The process of turning charcoal into biochar into better soil involves (as best we can determine) several steps:

• quenching with water that has minerals and biology in it;

• adding minerals and organic matter to the charcoal when it is pulverised; and

• mixing it with compost prior to application.

Our biochar mentor has access to a pig farm ‘lagoon’. That is a nice name for the dam where a mix of urine, faeces and water is stored before being applied to paddocks. It is pretty rich stuff. We have to make do (for the time being) with horse poo we get from a trotting track nearby.

After we have quenched the fire - and drawn off the quench water we take advantage of the tipping feature of the kiln (after removing the heat shield.