Biochar EN – Académie Permaculture de Tomate & Basilic

Biochar, or how to resuscitate a dead soil

Its utility, production and use: biochar, a new black gold for agriculture and the climate?

Biochar, or charcoal for agricultural use, has its origins in an extremely dark and rich land in the Amazon studied by scientists at the end of the 20th century: terra preta. They noticed that this land had been created by the Amerindians between -800 and 500. Indeed, during this period, the Amerindians integrated coal in the earth, giving it this color so dark and this great richness in carbon and in minerals essential for plant growth.

In recent years, biochar has been used again in agroecology, agroforestry and permaculture to amend and fertilize very poor and acidic soils. It can be produced by charring any kind of plant material, which can give different interesting characteristics.

If the biochar comes from wood or woody material, it will have a very high concentration of carbon but few nutrients (Magnesium, Calcium ..). On the contrary, if it is from grass like hay, it will be relatively low in carbon but will contain many other elements.

As always in permaculture, you must therefore know your environment and soil before using biochar to determine which type you need!

The dual utility of biochar

Biochar has interesting properties, both for agriculture and for the climate and the environment.

Agriculture first. Biochar is a powerful and natural fertilizer that allows very poor and acidic soils to be amended to make them fertile and stable. It acts like a sponge that will diffuse water if the soil is dry or absorb water when it is too full. If the soil is sandy, it can go so far as to double the water holding capacity of the soil, while if it is clay, it will on the contrary allow the surplus to drain better. It acts in such a way as to always return the soil to a stable equilibrium situation, which is generally ideal for our crops.

For the climate and the environment, biochar acts on two levels:

by sequestering carbon in the soil, and therefore preventing it from ending up in the form of CO2 in the atmosphere
by filtering rainwater before it reaches the water table, which greatly limits the pollution of the latter by human activities

Emerging criticism

Some criticisms are nevertheless felt because if the biochar is very interesting at the level of the ground and the environment, some put forward the fact that, to produce it in industrial quantities (and therefore in sufficient quantity from the point of view of sequestration and agriculture), immense amounts of organic matter have to be carbonized. This is a problem that operates on two levels:

in terms of the energy consumed (and its discharges) to produce biochar which could cancel out its beneficial effects
in the forest from which organic matter is extracted. Its disappearance from the natural cycle of organic matter returning to the soil can prevent the forest from regenerating and eventually destroy it.

There is also the question of our right to sustainably modify poor soils around which unique ecosystems have developed: soil enrichment could destroy these ecosystems.

Obviously, these criticisms are being researched and ways to avoid these problems are being investigated.

Handcraft guide

To make biochar, all you have to do is carbonize plant material in a pyrolysis process: the plant is heated to a very high temperature, without allowing it to burn by preventing the supply of oxygen necessary for the formation of flames. The following video shows a simple and effective method of making biochar that you can reproduce at home.

The video is in French, you can add English subtitles on Youtube if you want to

The use of biochar

First and foremost, biochar cannot be used under all conditions: it acts like a sponge so it must be soaked in water before it is used. Ideally, it is advisable to incorporate compost or potting soil (up to 50%) to further concentrate the nutrients.

You can then integrate it into your soil by mixing it 20 to 30 cm so that it is well distributed in depth. A quantity of 1L of charcoal for 10m2 is sufficient to amend your soil and you can do it over several weeks or even years to strengthen it in the long term.