It started yellowing last year after transplantation. Perhaps it was to old to be moved (transplantation stress)? Fungal disease? I'm afraid it will eventually loose all of its needles. I gave it liquid fertilizer several times throughout the previous year. Recently I added some organic fert.(manure). Not sure about the exact soil pH, but it was not acidic at the time. Btw, I threw some gypsum powder around the pine 6months ago, soil was somewhat hard.