It’s possible to get char for Terra Preta from rice husks, the hard shell surrounding rice seeds which is often discarded and burned as a waste. The burner detailed here produces char with each rice husk fuel load if it is fired once, fired twice and you get ash. It’s being used as a replacement for LPG stoves in the Phillipines. I am sure it could burn a lot more than just rice husks, which would mean that it could replace heating furnaces and gas stoves in even developed countries.
http://www.crest.org/discussiongroups/resources/stoves/Belonio/Belonio_gasifier.pdf
It produces a gas which burns. I do wonder whether the waste heat could be used to power a stirling engine boiler and electricity unit such as the ones that are being produced by Whisper Tech of New Zealand as a combined heat and power unit (CHP) for home use.
http://www.whispergen.com/
That way you would get cooked food, heat for water and electricity from the one unit. Then when your fuel is spent you can take it out and grow vegetables with it.
CHP is an incredibly efficient way to burn stuff.
