I was interested in using biochar due to my excessively draining soil. My timber-company neighbours just made a bunch of burn piles. Does it make sense to collect the char (excluding the ash) to make my own biochar?
There was a guy named Michigan gardener who advocated using charcoal for barbeques on You Tube. He mentioned that it would go away after 3 years and you'd have to put in more. I think the problem with this stuff is that it isn't burned to the point that it becomes char. It still has volatile oils, burnable wood, and natural plant products in it, so it is partway in between being wood and char. One strategy you could use would be to burn it intentionally to try to make char, which wouldn't take as long as one would if he were starting with regular wood.
I burn my wood until the flame dies down to just above the height of the char. Then I know it is ready to be doused with water, to stop it at char and prevent it from becoming ash. Before I do that, I normally try to chop it until the pieces are roughly similar. If I don't do that, the big wood pieces are still burning when the others are done. Then I crush and inoculate it with nutrition. There are usually a few larger pieces that get reburned in the next char.
Another alternative could be to just keep replenishing it every 3 years like the Michigan gardener guy.
I also live in the PNWet and we do have acidic soils. That's one reason I was motivated to make biochar and try it out.
I usually drench it when the flames are just 3-4 inches above the char. I find that to be the best timing. I have tested it empirically, and that way I don't get a lot of pieces of unburned wood, which happens when I drench it when the flames are too high and active. I also don't get a lot of ash, which happens if I burn it too long. I get very light, jet-black metallic, musical sounding char. Then I crush it and give it nutrition, and it becomes biochar, ready for the garden.
People use different supplements. I usually give it worm compost, regular compost, rotten wood mycelium, whole wheat flour, rotten fruit, and crushed oyster shells. Then I soak it in urine. Some people add seaweed, compost tea, or any other nutritious organic material. Some people will put it in the compost pile and leave it for awhile.