I agree with Michael, it is only redundant if you know for certain that the wood ash in question has a good boron content to it.
I was recently at a field day at UC Davis and the discussion turned to the high boron content in the well water around the campus, itself, and surrounding farms. Many growers see boron toxicity often and regularly test for its presence in the soil and in tissue analysis.
A&L Western Labs offers a soil test specifically for Boron for a mere $8
here is a link to see that test as well as dozens of othersIf you really want to test your wood ash for boron (and any other trace minerals) call a reputable soil lab and ask them what they suggest. Might be relatively easy to do. If you do it, post up the results to our forum. Would be an interesting reaad
You may have a good Ag soil testing option locally, including some universities, that can do exactly the same thing.
Good luck
Gopher Hill ApplesZone 8 in California