The use that comes to mind is as a soil amendment, but it appears to have limited value.
"A Source of Calcium for Plant Growth? Yes, the calcium from gypsum can be taken up (absorbed) by plants. Amount of calcium needed for crops, however, is relatively small."
"A Liming Material? There has been some suggestion that the application of gypsum will raise the pH of acid soils. Although gypsum, like lime, contains calcium, the calcium is not responsible for an increase in pH where soils are limed. It is true that the use of gypsum increases pH when applied to acid soils in the southwestern United States. That increase is due to complex reactions with soluble aluminum. Soluble aluminum is certainly not a concern in Minnesota soils. Therefore, we can't justify the application of gypsum as a liming material."
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.
