Gypsum IS calcium and sulfur, plus oxygen (CaSO4). The AST part means 'Advanced Soil Technology'. I've never used it, so I can't say how well it will perform. The coating might swell up a lot in soils (see link below), but it's only 2% of the product.

Al

Calcium Sulfate-Dihydrate (CaSO -2H 0) .......................................... 92%
Calcium (Ca) ................................ 20%
Sulfur (S) .................................. 16%
16% Combined Sulfur (S)
Derived from mined gypsum (calcium sulfate dihydrate (CaSO -2H O)) F14

ALSO CONTAINS NONPLANT FOOD INGREDIENTS:
SOIL AMENDING GUARANTEED ANALYSIS

ACTIVE INGREDIENTS
1.5% Polymers
1.0% Anionic Polyacrylamide Copolymer (Emulsion)
0.5% Anionic Polyacrylamide Copolymer (Solid)

INERT INGREDIENTS
Gypsum ...........................92%
Lignosulfonates (Binding agent) ........................... 2%

Here is a link that might be useful: Read more about the polyacrylamide coating

Thank you. I have -no- idea what I'm doing... hoping I don't kill the tangerine seedlings I've been nursing along.

You can be sure we're all hoping right along with you. ;-) Good Luck!

Al