Some notes on my lab report (above):
- Calcium saturation is high, with 6k parts per million and a ph of 7.1. The recommendation (at the bottom) is for 257 pounds of sulfur per acre to flush out some of the Ca and drop the ph to a 6.8. The recommendation takes into account the high Calcium Exchange Capacity of my soil (which corresponds to the buffer capacity -- meaning I need more sulfur to affect a ph change). I need to reapply sulfur every year or two, since my irrigation system re-introduces calcium.
- I'm lacking in potassium and magnesium. The recommendation is for 61 pounds / acre of potassium and 18 pounds / acre of magnesium. I can satisfy this with k-mag (sul-po-mag or langbeinite), which is an organic product.
- Copper is low. I can satisfy that by spraying a higher concentration copper fungicide (I got the highest OMRI listed copper fungicide on the market -- Nordox 75 WG). In this case I can kill 2 birds with one stone, controlling anthracnose via a foliar spray and enriching the soil with the runoff.
- Manganese is low. This is very typical of south florida soil. I'm using manganese sulfate. I haven't been able to find a local supplier of granular manganese sulfate, so I've just been using Tecmangam, which is a powder. Generally it's not recommended to broadcast it (due to leaching), but given the high CEC of my soil, it should retain a lot of the Mn with a broadcast treatment. I will report back on this after next year's soil sample. The recommendation of 3 pounds per acre is apparently for a foilar treatment, as a broadcast rate would be 10x that.
- My soil has a fairly high nitrate level, due to the monstrous quantities of mulch I have added over the last decade. The recommendation for 50 pounds / acre nitrate would probalby only be valid if I were using a synthetic N fertilizer, which would leach quickly. I haven't used nitrogen fertilizer in many years.
Marl, or soil with ridiculously high levels of calcium is an entirely different ballgame in which some sulfates are not effective, and micros need to be applied via chelate drenches or foliar sprays. But, in my case, I can bring the pH down to neutral and below with sulfur. I do have a layer of limestone just beneath my soil, but I have built up a 10 - 12 inch layer of compost + sand on top of the limestone that I can keep at a neutral ph. The feeder roots thrive in that layer of compost, while the anchor roots dig down into the lime stone rubble.
As a very rough rule of thumb, I think you can effectively modify the pH of your soil if the Ca content is under 1% (or under 10k parts per million).