I'm happy to see someone mention this. Too often there are those who justify their heavy use of wood ashes by saying that they've been rained on a few times and therefore neutral. Although most of the nutrients and salts will have been washed out by the rain, the end result is that the ashes then are even more alkaline, not less.In other words, the pH neutralizing effects of soil amendments do not "leach" down deep through the soil profile.
Farmers in Minnesota...especially Northern Minnesota....have been using "industrial" wood ashes for years. Paper mills, oxboard manufacturers, plywood manufacturers and other forest product companies, as well as, some power plants have wood ash as a by-product. Most of the time it is delivered to the farm for free.