Thank you Andre for your comments. I have been working on increasing Ca with gypsum, which I hope will improve the S as well. A soil test shows that Ca is high in comparison to Mg. (Ca:Mg = 76%:10%). My main concern is the Mn, as this can regulate K which in turn can regulate Ca, but I am not sure in which form I can best introduce Mn (Mn EDTA is the only thing I cabn easily get here and I try to avoid EDTA).

My other thoughts are that the high Fe levels in the soil are somehow blocking the Mn uptake.

I plan to make a LAB from Manganese Sulfate.

Any other thoughts?