One source of gypsum is old sheetrock. Not being one to waste a resource, I've been using it to add the gypsum. It takes forever to break into useful small bits for incorporation into the soil.
So today, I tried using my Corona grain mill. I fed it busted up chunks of sheetrock and easily got out nice, easy to spread and incorporate particles. It's much faster than the hammer and flat rock method I was using before.
/johnny
A new use for stuff is always nice.