Gypsum does not change pH nor improve drainage in non-sodic situations. Gypsum is used to add calcium to soils such as serpentine with very high or toxic Mg levels.

Does gypsum alter soil pH?

Gypsum (calcium sulphate): Great for acid loving plants (like rhododendrons) as it adds calcium to ground without altering soil pH. Also good at breaking up clay, especially reactive clays and can improve the structure of most soils.

What does gypsum do to pH of soil?

Gypsum will change soil pH very slightly, yet it can promote better root development of crops, especially in acid soils, even without a big pH change. This is because the gypsum counteracts the toxic effect of soluble aluminum on root development.