Making Biochar is an immediate way of beginning to tackle the vexed problem of carbon dioxide and methane emissions. I’ve decided to try and bring it to the attention of a wider audience so that anyone can experiment in their back yard.
- What is biochar?
Biochar is made from wood or woody plant material. It is cooked in the absence of oxygen until all the volatile elements have been driven off, leaving the carbon behind. Since oxygen is excluded the carbon does not burn. This process is called pyrolysis. Another term you may come across is ‘gasification’ which focuses on the gaseous by-products of pyrolysis.
- How does it lock up carbon?
The carbon dioxide utilised by the tree to make sugar and then timber is rendered into a fairly inert form of carbon called wood. By pyrolysis we are able to separate the carbon from the more volatile fractions of the wood. If the carbon is then utilised in the right way, the carbon that came from the air is retained as a solid. From timber that is dry, it is possible to lock up about half the carbon involved using modern pyrolysis retorts.
- How can we preserve biochar for centuries?
You might be tempted to landfill it but like coal, someone in the future might decide there was a profit in mining and burning it. Fortunately, there are better ways of utilising biochar. It makes a very effective soil improver. Adding around 3-10% by volume to poor soils can have a dramatic improvement effect on crop yields. If the biochar is mixed with compostable material, the biochar provides a home for mycorrhizal fungi and bacteria which help break down the compost and feed plants. Biochar is porous to water and air. The amount of internal surface area in a lump of biochar is colossal. Water, fungi and bacteria will cling to the internal surfaces turning each grain into a reservoir of resources available to plants growing in the soil.
- How do we spread biochar across fields?
Strange as it may seem, one answer is to add it to the feed of farm animals. It passes right through their gut without being broken down and ends up in their dung. By spreading the dung on the fields, you are adding bacterially and chemically charged biochar to the soil along with the very stuff that earth worms are going to drag into the soil. Since at normal outdoor temperatures, the biochar does not break down, you can build up a fairly permanent improvement in the soil. The farm animals seem to like having biochar added to their feed. Ruminants in particular benefit as the biochar favours the aerobic bacteria which break down grass into bioabsorbable sugars and discourages those that produce methane. This may improve the food conversion rates and reduces the need to burp out methane, a very potent greenhouse gas. Reducing the amount of ‘wind’ probably makes the animals feel more comfortable. Another way of preparing biochar is to mix it with things like worm casts or liquid compost made from comfrey leaves, nettles or seaweed. This can then be mixed directly with soil or potting compost. Digging biochar into the soil where the root system of your crops will grow improves drainage and aeration as well as sweetening clay soils. On a more commercial scale use a fertiliser spreader to apply biochar to the surface of a field prior to cultivation or add it to the fertiliser when drilling wheat or barley – just mix with the fertiliser and up the dosage rate set on the drill. Another use in a field would be adding to drainage. This would capture chemical run-off from a field before it pollutes water courses. Fertilisers would remain in the field. Imagine having a mole plough with a hollow blade and bullet through which biochar was delivered into the cavity formed by the plough. The plug that is dragged behind the bullet would press the biochar into the walls making them more porous and trapping the biochar in the walls where water seeps through to the mole drain.