As the name would imply, evaporite minerals form by the evaporation of sea water millions of years ago. Gypsum and limestone are two evaporite minerals found in Kansas and used for agricultural amendments. While both can be used to supply calcium as a fertilizer, they also have separate purposes.
Lime is CaCO3. Used to increase soil pH, it occurs as nodules of calcium carbonate deep in the soil profile in most of eastern Kansas. In western Kansas, it can occur very near the surface.
Gypsum, on the other hand, is CaSO4.H2O. It can occur in many forms — selenite is the crystal form, while alabaster is powdery. Most commonly used in Kansas to remediate sodic soils, a ton of gypsum contains about 320 pounds of sulfur. Unlike lime, it does not affect soil pH — elemental sulfur is the correct form for reducing pH. Gypsum is about 200 times more soluble than lime and is naturally found in the soil profiles of the more arid parts of the state. FGD gypsum (which stands for flue gas desulfurization) is produced at coal-burning power plants in the process of removing sulfur from air emissions, and is approved for land-application in Kansas.
For more information, see a 2011 Extension publication titled “Gypsum as an agricultural amendment” by L. Chen and W.A. Dick, Ohio State University, at: http://ohioline.osu.edu/b945/b945.pdf
For more on saline and sodic soils, refer to the eUpdate: