Been studying on how to turn clay to good garden soil, and one way seems to be using wood chips for mulch....just keep adding them year after year. Went to a presentation at the MEN fair couple months ago. Guy passed around a jar of his original dirt, then another after a year of wood chips, then another after 2nd year and so on. By the 3rd year, it was some darn good looking soil ! I just happen to have a good source of wood to make chips...slabs off my sawmill that here to fore had been going in a pile and burned when the pile got big enough and weather conditions permitted. I bought a WoodMaxx 8M tractor PTO driven chipper and plan to chip all my slabs from now on, as well as the normal accumulation of brush/tree tops around here. Cut about 1500 bdft of lumber last week, and saved all the slabs, plus I had some old poplar logs that were half rotted....cut them into stuff that will go in the chipper. It will handle up to 8" wide, and according to them, 6" thick....but I've found 3x6" is about the max slab it will handle without popping the shear bolt in the PTO. Put a couple hours in this morning chipping what I'd set aside, probably ended up with a single axle dump truck load of chips. Pretty much filled one of my compost bunks, which are 8x10 x 3-4' deep.