Hello,
In addition to plant available Calcium (about 22%) gypsum also contains roughly 17% available Sulfur. The phosphoric acid business produces mass quantities of gypsum as a side product, however trace quantities of radioactive elements have placed a voodoo on its potential to be a side product and it is normally used as a filldirt for the excavated mining area.In the fertilizer industry gypsum is used primarily as a filler in NPK Granulation/Blending plants (it is normally not applied directly to plants). To the best of my knowledge selling gyspum as a filler to fertilizer plants is a possible way to rid yourself of unwanted gypsum, however it must be in a suitable form (granular or fine powder) and the selling price is not such that the business would be lucrative.