During her Phd thesis under my direction Stéphanie Topoliantz obsrved that the peregrine pantropical earthworm Pontoscolex corehtrurus was the main component of the earthworm community in French Guianan slash-and-burn agricultural soils. She observed that it ingested charcoal particles which were mixed with mineral particles in its dark-coloured casts. She performed experiments on the ability of P. corehtrurus to ingest charcoal and mix it with the soil. She also demonstrated experimentally that P. corethrurus populations of slash-and-burn areas were differentially adapted to the consumption of charcoal. She also showed that charcoal could used in combination with manioc peels for improving soil fertility, rather than discarding them in the parcels to be cropped, as was common practice. Several papers were published:
https://www.researchgate.net/publication/44986525
https://www.researchgate.net/publication/44922028
https://www.researchgate.net/publication/44922021
In a short synthetic paper I suggested that P. corethrurus could well be the main agent of the formation of Amazonian Dark Earths, in which incorporation of black carbon (issued from charcoal) was considered as a main agent of durable soil fertility (see article and books by Bruno Glaser and Johannes Lehmann):
https://www.researchgate.net/publication/44735820
Since it has been shown that in Pre-Colombian times sedentary agriculture existed in Amazonia and charcoal was used as an amendment (originating in present-day Terra Preta), we may wonder whether this very common tropical earthworm could not be used to improve the application of Biochar, based on its ability to crush charcoal particles and finely mix them with the soil.
Catch as catch can...
Article Ingestion of charcoal by the Amazonian earthworm Pontoscolex...
Article Manioc peel and charcoal: a potential organic amendment for ...
Article Charcoal consumption and casting activity by Pontoscolex cor...
Article Burrowing activity of the geophagous earthworm Pontoscolex c...
At the moment I have no answer for your question. In case I come across any article or document related to your question I will let you know.
Very interesting. Who would the chemist then? Who would transform this charcoal into available nutrients for plants?
Dear Inaki, there are many papers about chemical effects of charcoal particles (also called black carbon). Among many others read:
https://www.researchgate.net/publication/200736437
https://www.researchgate.net/publication/237079805
https://www.researchgate.net/publication/226309557
https://www.researchgate.net/publication/222161946
If you are interested I can send you a more complete bibliography.
In short, most effects of charcoal (when finely subdivided and mixed with the bulk soil, i.e. reworked by P. corethrurus, or man if necessary) are not direct (the provision of nutrients) but rather indirect, by adding to the soil fine particles with highly sorptive properties: they retain nutrients and water, making them available to plant roots in place of being lost by leaching. This is due to the plant origin of charcoal: wood vessels when void of contents (the result of buring) have a huge surface/volume ratio. Since most chemical exchanges in the soil are related more to surface than to volume, it is easy to understand what could be the advantage of adding particles which increase to a great extent the contact surface between soil skeleton (solid particles) and the soil solution in which plants find what they need for their growth.
Article Ameliorating Physical and Chemical Properties of Highly Weat...
Article Black carbon—possible source of highly aromatic components o...
Article Nutrient availability and leaching in an archaeological Anth...
Article Effect of Charcoal on Certain Physical, Chemical, and Biolog...
Presentation Vers une meilleure utilisation des traits fonctionnels des i...
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