The first time I heard about terra preta (the highly fertile black soils of the Amazon basin) and what made them, biochar , I was blown away. What fantastic stuff! Then we started hearing about people making it and it seemed so convoluted. Then people started coming up with backyard kilns to make their own biochar - and the scientific community started weighing in on the argument. Better not to make it at home. It had hydrophobic qualities unless it was made at a minimum of 450° C, they say. Could make the soil too alkaline. Could deplete the nitrogen in the soil initially.
Well, they are very possibly right. We may not be able to make biochar as well at home as under controlled industrial conditions - but when has that stopped us. And I'm pretty sure the Amazonians didn't have controlled industrial conditions! However, proceeding with caution seems a good idea. Make some biochar, and do your own experiments. Put some into the soils around some plants and don't put any around other plants. Keep everything else as much the same as possible. What is the difference?
We don't have a special backyard kiln. Instead, we live on a farm with wood heating. Every morning in winter we clean out the hearth. Within a few days we have a 12 L metal bucket full of ashes and charcoal. We sieve it to remove the ash, then crush the charcoal. To start converting it into biochar, we add the nitrogen rich nutrients and other goodies at this stage (chicken pooh is a good start – better in the charcoal than on the verandah!) because charcoal alone is like one of China’s ghost cities – apartment building after apartment building is empty. If you add charcoal straight to your soil, its empty structure will adsorb (not absorb - there's a difference) nutrients from all around thus depleting the soil of nutrients. Over time, it will become biochar, but your plants will get hammered until it has achieved this balance. Answer: fill the charcoal up with nutrients before adding it to the soil.
I think everyone who has been playing around with biochar for a while has their own favourite recipe or they may even have different recipes depending on the needs of the plants being grown. We’ll make our own version of biochar and you can see what you think.
Here we are cleaning out the wood fire, sieving the ash out and collecting the charcoal. By the way, we don't sieve the ash directly onto the garden anymore. Yes, it contains potassium, but too much potassium will make the clays in the soil stop working properly. Now we collect the ash and make lye for soap making etc. Two useful products out of what others consider a waste product. Robyn (see New from Old) will be proud of us!