Some studies are quite skeptical. For example,

https://asi.ucdavis.edu/news/new-study-biochar-helps-yields-...

https://journals.plos.org/plosone/article?id=10.1371/journal...

Some studies even show that biochar soil amendments accelerate the breakdown of humus and release net positive CO2 to the atmosphere:

https://onlinelibrary.wiley.com/doi/full/10.1111/gcbb.12376

> However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common.

> Our results showed that biochar application increased soil CO2 fluxes by 43.33% in unfertilized soils, but decreased by 8.61% in N-fertilized soils, consistent with the meta-analysis of Liu et al. (2016).

The metastudy did go into detail about N2O and CH4 as well in both fertilized and unfertilized soil.

Burn, by Albert Bates and Kathleen Draper (2019) - goes into the multitude of ways biochar can be utilised. It's a bit heavy, but in a good (here's the research that backs us up) way.

https://www.chelseagreen.com/product/burn/

I can also recommend this wikipedia article and its surroundings:

https://en.wikipedia.org/wiki/Terra_preta

I found these videos very interesting:

https://www.youtube.com/watch?v=svNg5w7WY0k&t=5s

This is on my to-do list:

http://climatechangeacademy.com/courses/carbon-removal/4

https://bootup.airminers.org/

I found a lot of information from comments here:

https://news.ycombinator.com/item?id=27822694

As others have noted, the wikipedia entry is a great resource.

I was introduced to it on this podcast episode: https://podcasts.apple.com/us/podcast/permaculture-for-the-f...