Creating charcoal and assembling a kind of synthetic "terra preta nova" has the added advantage that while the charcoal is being formed by pyrolysing biomass, BioOil and BioGas are simultaneously produced. Ideally, the gas can be used as the fuel for the pyrolysis and the oil can be mixed to an extent of 25% with conventional liquid fuel, in the intention that by 2025, 25% of the U.S. oil requirements will be met by means of it: hence the name of the "25x25" club, a political group with this outcome as its primary agendum. It's a tall order and some of the estimates of how much biochar can be made are staggering, up to 9.5 billion tonnes/year, which I don't think is realistic either in terms of land use (growing enough biomass) or building bio-mass pyrolysis capacity on this immense scale. This is an estimate by Professor Johannes Lehmann form Cornell University, whose expert opinion I respect, but I don't see it personally since it amounts to producing about one tonne of biochar/hectare on two-thirds of the entire land surface of the Earth (95 million out of 150 million km^2).
The International Biochar Initiative (IBI) are working to a more modest 1 billion tonnes/year by 2050, and I reckoned recently that almost this amount could be produced in total throughout a collection of world-wide small communities in which each person made 100 kg of biochar per year - or it was collectively made for them within the activities of their community. The latter strategy cuts-down the prohibitively massive centralised plant-engineering required, if it were done this way, to more manageable chunks.
Now, there is the proposition of a connection between biochar and microbial life in terra preta soils, in which mycorrhiza fungi thrive and produce glomalin. I have noted that there is strong evidence that this glue-like glycoprotein is significantly responsible for the storage of organic matter in soil and for soil health. There is speculation that glomalin is the secret of terra preta soils/biochar as a consequence of the elevated fungal population (thought to thrive in the carbon micropores). Glomalin is produced by hair like hyphae filament structures of fungal bodies.
Overall carbon capture and humification in soil is probably the long-term process by which terra preta soils are produced and I wonder how long it would take for a soil, simply amended by charcoal, to become a fully-fledged terra preta with the properties noted. I envisage it is not likely to be an immediate event, and probably the Amazonian indians created these soils over many years, to their fully self-generating glory. The native people described the soil as physically "growing", which may suggest an accretion process involving fungi and other microbiota.
There is an interesting discussion of some of these topics at the link address below. I would be grateful for any input from those who know more than me about these things.