I've found cardboard to take a while to break down here (should be gone toward the end of next summer, but probably not by spring) and I wanted the char closer to the root zone of the berries rather than over the cardboard. I added the bedding/manure under the cardboard because I'm not totally convinced that the char was fully charged with nitrogen etc in my quench. Mostly I'm throwing stuff at the wall, the main variety of raspberry (doublegold) has been vigorous for me, so chips over cardboard would probably work fine, but I had char and manure too.
Discussion
Thank you! this is very helpful. my guess is that the cardboard will take a while to breakdown for me as well, so I may try another area with your layering order to see how that works.
For my fruit trees that were already in the ground before we started making biochar, I've been adding a layer of it under compost/leaves/mulch and just hoping that at some point it works its way into the soil.
I'm sure it will, especially the smaller pieces as the soil critters do their work.