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As there have been quite a few questions asking about biochar I thought I would dedicate a thread to explaining what it is.
Basically biochar is a form of charcoal made from woody waste that has been charred at a relatively low temperature, with a restricted supply of oxygen. The process is called pyrolysis. The result is a very stable form of carbon that is proven to be an excellent soil amendment that leads to healthier crops and can also reduce atmospheric concentrations of CO2 when buried in the ground.
Biochar has been referred to as ‘the oldest new thing you’ve never heard of’ which is a pretty apt description given that not many people seem to have heard of it. It is not commonplace in British horticulture although it has been a by-product of traditional woodland management in the UK for many years, along with charcoal making. But use of biochar goes back even further than this.
Knowledge of biochar and the benefits of adding it to soil have been around for millennia. Studies of soil at sites throughout the Amazon Basin suggest that ancient Amazonian civilisations made a type of biochar and added it to their soils to help grow their food. The result was a rich and fertile black earth - or ‘terra preta’ - with a high carbon content, which is still evident today.
The attached pic (if it works!) is an extreme close-up (from a scanning electron microscope) of the structure of biochar which shows why it works so well as a 'refugia' - the pores of biochar provide a safe haven for beneficial microbes such as mycorrhizal fungi and associated bacteria. This ensures their populations are resilient in the face of predation from other soil organisms such as mites, protozoa and nematodes. Thanks to the UK Biochar Research Centre for this one.
