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If you have a calcareous soil, it's almost impossible to buffer it with sulfur.
Yes, you can use the two together. That's what I do. The top several inches of my soil is Ca deficient, being mostly black compost (the ratio of Ca to K is too far towards the K end). So, I use gypsum to add Ca, which has had notably positive effects on brix, flesh firmness, and flesh color. I use the sulfur to lower the pH to the low 6'es.
Sulfur will take a while to alter your ph significantly, maybe a couple of years. Why are you using calcium sulfate?
isn't gypsum the same as calcium sulfate? I googled it and they use the words interchangeably
Certainly you can't permanently drop the pH unless the amount of free calcium carbonate is small (eg, below 1%). But it is possible to achieve some temporary acidification which can be replenished every so often with a fresh batch of sulfur.In my case, the top 12 inches or so of soil is sand plus compost, which I've been able to acidify quite easily. The soil beneath that (which is more calcareous) is much more difficult to acidify. But feeder roots live in the top 12 inches of soil, so it's a moot point :-).
Why don't you use AMMONIUM sulphate?You add nitrogen and you lower the pH . The effect is fast