By Julie Macbeth
It’s interesting how life works. I had heard the term ‘Biochar’ before, but had passed over it. It came up again when I visited a fellow Tree Crops member's garden, but again, I let it slide. On returning home, I decided it was time to educate myself on this, new to me, concept. As a long-time gardener and advocate for the planet I became quite fascinated by what I learnt. Not only can biochar provide long-term carbon sequestration, but it can also improve the soil when it has been inoculated with a fertiliser agent. Almost immediately, an opportunity to be involved in a Biochar Field Day hosted by NZ Landcare Trust and Slow Farm Ltd arose, through the Environment Network Manawatu newsletter.
I attended the workshop, and from the perspective of a home gardener, have been inspired by the various presenters to embark on my own biochar venture. Four different methods of making biochar were demonstrated, with each advocate giving freely of their enthusiasm and knowledge to encourage others to take up the challenge. Massey University are engaged in research into biochar properties, the carbon footprint of biochar, and the economics of small scale biochar production, and have a mandate to share their findings with interested parties - meaning you and me!
Whether you are a home gardener or a large land owner, there is a method of production to suit your use. There are some complexities regarding method and materials used in production, but these can be regarded as a learning curve and it’s probably best just to dive in and get started. The simplest method is to just dig an inverted cone shaped hole to start your fire in. 70 degree angles to the sides work best as this creates a vortex of air flow over the top which keeps the flames and gases spread over the surface layer and prevents the air/oxygen getting into the deeper layers as you build the fire higher. One demonstrator had a ring of steel made which was placed on the ground over a smaller hole, reducing digging work if it was required to move it.
Another model was the kon-tiki kiln which is a stand-alone unit that can be transported anywhere.
There was a trough type arrangement, and also a wood-filled drum that was placed inside another container with a chimney on it.
When the burning is deemed finished, the open fire methods are quenched with water. This seemed to me an important step, as it opens the pores of the charcoal, producing an even great surface area for interaction with soil organisms and moisture retention. Some methods miss out this step. After cooling, the biochar is crushed to 5 cm or smaller pieces, and then inoculated with your own brew of fertiliser to activate it. This could be a tea of any manure, seaweed, comfrey, etc.. It can also be mixed into a compost.
The scope for experiment with burning and inoculation materials is wide open, and could keep any curious gardener occupied for some great amount of time while they evaluate the results they achieve in production. Myself, I have procured two 44 gallon drums, and am going to use them lying on their sides, after cutting out an opening that leaves me with a nice curve, that hopefully encourages a vortex air flow on the top of the fire. Using the drums means I will also be able to retain the quench water which is full of minerals, and could be used in the making of a fertiliser tea. I also think digging a pit is a valuable method for the home gardener, if you have one area you collect your prunings etc in. There is a wealth of information out there on biochar production - hopefully more and more people will take up the challenge.