CAT Biochar

Our relationship with the soil is a complex one, and the way that we treat this resource is crucial to the sustainability of farming and food security, as well as the capacity of the land to retain and absorb carbon.

Biochar is an increasingly popular product, a means of storing carbon dioxide from the atmosphere in the form of charcoal. This charcoal can then be permanently stored in the soils in a stable form.

At the same time charcoal can be used as a soil improver, absorbing nutrients that can then by taken up by the plants when necessary. Biochar or 'agrichar' is therefore being hailed as a major breakthrough for the future of soil management, but is in the early stages of being researched.

The concept of using charcoal in this way comes from the discovery of 'terra preta' in the Amazon. Through a process of 'slash and char' which was practised for thousands of years, the indigenous peoples of the Amazon created a rich, fertile black soil beneath the thin and fragile top soil. It is now known that this black soil has a remarkable capacity to retain nutrients for centuries, and release it to plants.

At CAT we have tested the capacity of charcoal to act as a soil improver. We make our own charcoal in a retort. This system is more efficient than a traditional kiln because it burns off the wood gases before they are able to escape into the atmosphere. It is also a much quicker method. This process is taught on our charcoal course. This charcoal was soaked in urine for a month, and then added to soil. Against a control, the biochar incorporated soils produced much larger bean plants. The clay soil was also given better structure by adding the biochar, enhancing the drainage capacity. We are planning open field trials to begin early next year to test the long term effects of adding charcoal and the best means of application.