Start a biochar plant burning biomass for energy but leaving the charcoal as a long-lasting soil improvement and carbon storage product.

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

Sell the biochar to homeowners:

http://www.ultrakulture.com/wp-content/uploads/2015/10/4-Ter...

I have no idea about the economics, though, maybe it's just not feasible without subsidies.

Edit: Why? Because the technique is simple, biomass is relatively cheap, you get electricity and heat you can sell in a cold climate, and that terra preta example makes me envious, as someone interested in gardening. If the char was cheap enough, I would want to buy lots of it myself. Helping the planet and helping my own plants.

I think you need a large scale plant to keep costs down. There are large scale biomass power plants where I live, but they specialize in burning everything, so some investment is needed.