Dave,
Contrary to the idle speculation of some, I had a friend whose business was restoring antique clocks. He packed his wood in dog @#$%/!! and buried it in his garden to age it. This was for oak and walnut only, both of which are rich in tannins.
I suspect the theory behind it is that feces are acid rich from digestive juices. Burying the wood allows those acids to permeate the wood due to moisture in the soil from rain. Even without the @#$%/!!, wood will age rapidly if buried. He left his buried for several months. Contrary to conventional surface aging which is fake aging with new wood underneath, this will give results deep into the wood.
One can only experiment by burying a couple of 1x4's and observing the results.