If charcoal (or biochar as it is commonly known) is buried in the soil, it can help retain nutrients and water, increase fertility and fix carbon in the soil for hundreds or thousands of years; thus removing up to 25% of the world’s carbon from the atmosphere. Or so it is claimed.
The idea originated in the knowledge that in Amazonia, dark soils dating from pre- Columbian times are extremely fertile and nutrient bearing. They were created in a long period between 450BC – 950AD by a lengthy, labour intensive process, which involved incorporating charcoal, animal and plant residues, including bones, and manure, over more that twice the land area of Great Britain. It’s thought they resulted from a process of slash and char rather than slash and burn which produces ash.
More recently a large number of trials have shown that a variety of sources of biomass can be used to produce charcoal. Forestry and animal wastes, wood coppicing and other plant material can all be processed using pyrolysis, which burns slowly without oxygen and produces charcoal and gas which can be used for heat. If sewage is used for biochar it radically cuts the fuel costs and carbon emissions from treating the sewage. Some studies around the world claim remarkable results in poor soils, sometimes almost doubling plant growth. In the United States a trial showed that biochar doubled the capacity of the soil to store organic carbon. So it can save water, increase crop yields, reduce the need for carbon intensive fertilisers and remove CO2 from the atmosphere – magic!
But like everything else in this climate changing world we inhabit, not everyone agrees. The dark soils, some say, took many, many years (and lots of hard work) to reach their current fertile condition. Just digging biochar into our fields may not achieve quite the same result. Others claim that the biochar isn’t stable in the soil, losing its effectiveness in a much shorter period of time. And there is a familiar argument, similar to that used about biofuels, that biochar production will remove land from growing food, or involve throwing people off land that isn’t economically productive, or adding to the destruction of rain forest. On the other hand, it’s claimed that there are six billion tons of forestry, agricultural and animal wastes available every year. At the moment, the world’s financial systems reward energy production from waste and other sources, not the production of biochar. This may change, since there is a strong lobby for a massive scaling up of biochar production.
Locally however it could work. We could produce stoves that use biomass for cooking that also produce charcoal for our soil, reducing air pollution at the same time. We could use the organic waste from farms and homes in local pyrolysis burners for biochar to be put back onto the land. Doing this would avoid the ethical issues which query whether large-scale, intensive biomass cultivation is consistent with moves to a more sustainable zero-carbon future.
To find out more about biochar, a good place to start would be the Schumacher Briefing written by James Bruges, an ex-architect and environmental writer. Or come to our next Forum 21 meeting on May 27th when he will be talking about it. It will be at the Methodist Hall in Minehead at 7.30pm. All welcome.