Lately I've been dealing with high pH sandy soils, trying to help different people get their gardens performing on limestone. These are common along the western coastline of Australia right up into the tropics, and I know certain parts of Florida and the Keys have the same issues. These soils are basically marine derived and have large amounts of Calcium carbonate often in percentages in the soil. Dropping the pH even a couple of points can be extremely difficult due to the actual presence of pure Calcium carbonate rocks in the soil. Typically these soils are in excess of a pH of 8 and can go right up into the 9's. The theory is, if your raw soil has a pH of 8.4 or above you are basically fighting a losing battle as you may have up to 5% pure limestone in the mix. This is because what ever acidifying agent you put into the soil must react with all the available calcium carbonate before the pH will start to go down at all. This can require enormous amounts of sulfur, iron sulfate or ammonium sulfate, and in most cases this is totally impractical.
The biggest problem with high pH is that it locks up iron first rather tightly. So iron is the first deficiency you'll see, that is yellowing new growth, that may eventually yellow out the leaf veins and in extreme cases cause a serious whitening and then sunburn of the leaf. Usually these extremely deficient leaves can not be brought back. High pH can also lock other trace elements like Manganese, Zinc, etc.
I came across this interesting way of getting iron deficient plants growing on limestone soils healthy again, and to me it makes sense. It should be applied with some sort of acidifying action to the surrounding soil, but this technique should give trace element deficient plants a shot in the arm while the rest of the soil takes it's time to react with other treatments.
Basically you get one cup (approx 230g) of iron sulfate, and mix it with 10l (a bucket) of compost, well rotted manure (NOT CHICKEN MANURE), or peat. You then dig a series of holes about 1ft deep or more around your deficient palms and plants, and stuff it full of the iron rich compost mix. You then water it in heavily. Eventually the roots will in theory make their way into these pockets of rich nutrients and because they are quite strong, the surrounding limestone can't lock up the nutrients quickly. This treatment is meant to last a few years, although it would depend on the pH of the soil and nutrient demands of the plant. Also you could probably add other trace elements this way, but of course not going over the 230g/ 10L bucket ratio.
I thought this may be of some use to those on Palmtalk in similar situations. I know that Wodyetia's can seriously set back when the pH is high. They can get all sorts of nutrient and growth issues then fungi come along and finish them off. I hope this can be of some use to others, and it would be interesting to hear what others think of this treatment.
Best regards
Tyrone