Some of you might be interested in topic that is currently active on the tree forum. Lot's of really good information.
Here is a link that might be useful: Soil Ammendments
Back Yard Guy:
Really interesting thread. Thanks for sharing that with us. For the last few years, I have tended to plant the trees in the soil as is, top dress the bed with amendments (manure, compost), mulch, and let the worms go do that voodoo that they do so well.