Hi Adrian, when you say you are applying magnesium sulfur, are you referring to Epsom salt? Can you apply as a foliar rather than a soil application? Epsom salt is about 10% Mg so if that’s what you are using you’d be adding 20 kg/ha/yr Mg, which will never be enough to significantly raise Mg base saturation on a soil test. What are your soil EC levels? Are they increasing? What is your pH?

You are probably stuck with the high Ca base saturation. Sulfur will generally combine with Na first, then K, then Mg, then Ca, so it would be difficult to reduce Ca base saturation. You would also need enough rainfall/irrigation to leach the nutrients below the root zone to make it work.

If available in your area you could run a soil test that reports total nutrients in the soil rather than just ‘available’ nutrients to see what you are up against.