- Agricultural waste
- Municipal plant waste
- At least some animal excrement (great source of minerals)
- Algae?
- Seaweed (kelp)? (great source of minerals)
- Coppiced tree plantations?
- Biomass grown for biochar?
For each of these, we'll want estimates of amount available, difficulty (energy and money invested), suitability for biochar and/or landfill, and alternative or existing uses.
