Jim Porter recently told me he was not wild about bio-char because this might be a better use of the wood. I've done this unknowingly in the past but vs. a raised bed, filled pits with the wood then buried it. Very interesting concept! I am in the process of turning my old apple snail pond into a giant Water Wise Container Garden by having stabbed the sides in many places with a machete about 2 feet from the bottom to turn it into a bog garden in which to grow my new guava tree and my long-suffering jaboticaba tree......I'll ask the Universe for some log sections to toss in too along with the soil and mulch, etc. Plus I will start burying the wood waste I've been putting around my banana clumps.
Thanks for this link Jim! John