North American Fruit Explorers mailing list at ibiblio

[Alan Haigh <alandhaigh@gmail.com>]

"I did read that calcium sulphate was an even better source of sulphur to
acidify soil; have not tried it though."

I wonder where you read that.  Calcium sulphate or gypsum is used in sodic,
alkaline soils with insufficient calcium to avoid raising the pH in soils
already too high.  In such soils that are clays it helps separate the small
particles, creating better drainage.  That last sentence is from memory so I
may not have it quite right but basically gypsum can improve sodic clays.  I
never encounter such soils here in the northeast so I don't have to have my
facts completely straight.