All About Biochar

Biochar-enhanced garlic field

Biochar is great for farms – getting rid of those old corn stalks and the like, and enriching the soil at the same time. It's also ideal for people who normally cook over an open fire – no more smoke, much less wood.

What about those of us – the majority in Western countries – who live in cities, with very small gardens? Well, we can make biochar too, and reduce city air pollution and the pile of green waste going to the landfill, be well prepared for power cuts and fuel shortages, increase garden productivity – and cook wonderful old-fashioned barbecues.

What is Biochar?

Take ordinary charcoal, saturate with nutrients and beneficial micro-organisms, then bury in soil, and you have a product that will do its job for millennia. Crops grown on soil enriched in this way are dramatically bigger, stronger and healthier than those grown in untreated soil.

This electron micrograph of a tiny piece of charred wood gives an indication of its huge surface area. The cell structure of the wood remains intact in the soil for millennia, providing a stable "home" for microbes, water and nutrients which feed the plants growing in the soil.

This and other beautiful images were made on an electron microscope by Jocelyn of

An electron micrograph of charcoal

Carbon sequestration and sustainability

There can be no doubt that our planet is suffocating in carbon dioxide. We humans have generated much of it by burning fossil fuels over the last 200 years. Getting rid of it, and returning the atmosphere to a sustainable state, is the over-riding problem of our time. We're all part of the problem; we can all be part of the solution!

The earth's major carbon sinks are the atmosphere, the oceans and soils. We're generally well aware of the precarious state of the atmosphere, and the oceans are also saturated almost to capacity. Soils, on the other hand, can be dramatically improved by the addition of carbon - indeed most agricultural soils are in desperate need of it. Their biological life increases, drawing even more carbon out of the atmosphere, increasing food production and quality, purifying water, reducing energy and fertilizer requirements, generally increasing biodiversity and thus, sustainability.

Sequestering carbon dioxide in this way is something that any home gardener, farmer or forester can do, by pyrolysing green waste in a small home-made stove or simple retort. It costs almost nothing, the benefits are immediate and spectacular, and it's far more realistic than any industrial carbon sequestration process invented to date!

Mitigating climate change

If we still needed evidence of climate change, the last 12 months have given that to us: super storms, floods, fires, droughts and erratic weather patterns all around the world, causing economic loss, misery and death. Are we ready to take the warnings seriously and do something about it?

While it is undoubtedly true that massive industrialisation based on fossil fuels is the main cause of climate change, it is unrealistic to expect it all to come to a screeching halt any time soon, despite the appalling consequences of "business as usual". Certainly, those who benefit most from it, the global financial elite, will not voluntarily give up their privileges. So what can the rest (99.9%) of us do? As it turns out, we can do quite a lot, just because there are so many of us, some solutions are cheap and simple to implement, and because we have so much to gain.

The degree of global warming, and thus climate change, is proportional to the amount of carbon dioxide (CO2) being added to the atmosphere. To stabilize the climate, CO2 emissions need to be drastically reduced. To actually reverse climate change, further emissions of CO2 must stop altogether, AND considerable amounts of CO2 must be removed from the atmosphere. Sequestering carbon in the soil is a partial solution - it won't cure climate change, but it could significantly mitigate it. Here are a few statistics (1) to make the point:

  • About half the carbon in the atmosphere at present has been produced by human activity;
  • Atmospheric CO2 level is now over 390 parts per million by volume (ppmv), i.e. almost 40% higher than the pre-industrial level of 280 ppmv; 
  • 350 ppmv CO2 in the atmosphere is considered the highest "safe" level, to avoid catastrophic climate change;
  • Atmospheric carbon has been increasing by about 4 gigatons per year over the last decade;
  • Soils world-wide have the potential to take up 1 gigaton of carbon per year;
  • 1 gigaton of carbon is about three times the amount of carbon emitted per year by all the cars in the US.

Clearly, burning of fossil fuels needs to be drastically reduced. On top of that, widespread carbon sequestration will be needed to reverse the upward trend in atmospheric carbon levels. As we shall see, biochar is a cheap and effectual means of sequestering carbon, and one that just about anyone can do.

Simple technology

The technology could hardly be simpler. It is easily adapted for use in the smallest garden, on a productive farm, in forestry operations, in city waste management systems, and is already being used effectively in alleviating poverty and its associated health problems in underdeveloped countries. (2)

City gardens: Garden waste can be easily turned into useful charcoal in a small pyrolysing stove, which may double as a home barbecue. A few stove models are being made, mostly for use in underdeveloped countries where women traditionally cook over smokey fires. Home gardeners can also have some fun making their own stoves from used food cans. To produce biochar, the charcoal produced in the stove is usually mixed with compost to inoculate it with micro-organisms and other nutrients before adding it to the soil.

Farm- and industrial-scale retorts: Green waste can be a problem on many farms, but, as in the city, waste can be turned into a valuable soil enhancement. Depending on the inventiveness of the farmer, a well-designed retort can produce not only charcoal but heat to drive a turbine or heat water as well. On an even larger scale, retorts are being used already in forestry and town waste management facilities, to produce electricity or useful heat. As in a city garden, the charcoal left in the retort is turned into biochar by inoculating it, then spread or ploughed into soil.

The principles are the same, whether applied to a domestic barbecue stove or scaled up to a farm or industrial model - plant material is pyrolysed by heating it in a reducing atmosphere (deprived of oxygen), leaving the carbon behind, and burning only the gases given off by the heated fuel. These gases are similar to natural gas, and burn cleanly at a high temperature.  


1. Albert Bates, The Biochar Solution, Carbon Farming and Climate Change, (New Society Publishers, 2010): p.76.

2. Albert Bates, The Biochar Solution: Chapter 23, Stove Wars.

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