Gypsum vs. lime: Facts about minerals
Evaporite minerals occur naturally in Kansas as geologic deposits. As the name would imply, these 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. Some facts:
- Lime is CaCO3. The chemical name is calcium carbonate.
- Gypsum is CaSO4.H2O. It can occur in many forms. Selenite is the crystal form shown in the photo below. The powdery form mined for sheetrock and agriculture is called alabaster.
- Lime and gypsum can both be used to supply calcium as a fertilizer.
- Gypsum contains sulfur (S) and a ton of gypsum contains about 320 pounds of S.
- Lime is used to increase soil pH.
- Gypsum does not affect soil pH. Elemental S is the correct form to use to reduce pH.
- Gypsum’s most common use in Kansas agriculture is to remediate sodic soils.
- Gypsum is ≈200 times more soluble than lime.
- Gypsum is usually only found naturally in the soil profiles of the more arid parts of the state.
- Lime 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.
- “FGD” stands for flue gas desulfurization. FGD gypsum is produced at coal-burning power plants in the process of removing S from the air emissions, and is approved for land-application in Kansas.
Figure 1. Gypsum (in selenite form) outcrop in Hodgeman County. Photo by DeAnn Presley, K-State Research and Extension.
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:
DeAnn Presley, Soil Management Specialist