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[Alan Haigh <alandhaigh@gmail.com>]

Phosphoric acid?   Well I won't be the one to try that out to grow blueberries- don't ever need to go very drastic here as soils tend towards the acidic and are never much above 7 and often in the low 5's.

 

Pine needles and pine wood do have less calcium than most hardwood leaves and wood, but you are certainly right that they don't have much of any acidifying affect.  I once tested soil beneath white pines that had been growing their for nearly a century.  I tested under almost a foot of pine needles.  The pH was identical to nearby grassland.

 

I don't think you really have to wait for pH to be homogeneously low to serve acid loving plants.  As long as they can get their iron from a very thin layer of their rhizophere, say directly beneath composting mulch or recently broadcasted sulfur, they seem to thrive-  even if the majority of soil is excessively alkaline.