> Biochar is the lightweight black residue, made of carbon and ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment".

You may be thinking of biochar specifically as a soil amendment, where it is sometimes loaded with probiotics and such:

https://en.wikipedia.org/wiki/Biochar#Soil_amendment

> She pointed out that when pre-charged with these beneficial organisms, biochar promotes good soil and plant health.