GYPSOIL alters soil chemistry. Soil particles and organic matter have negative charges on their surfaces. Mineral cations (with positively charged surfaces) are attracted to these negative charges on the soil particles. The number of exchangeable cations that a soil is capable of holding and available for exchange with the soil water solution is called the CEC. This is an indication of the level of nutrients the soil can hold. Clay soils tend to have a high CEC.
GYPSOIL is calcium sulfate dihydrate (CaSO4 • 2H2O). It dissolves (dissociates) with moisture into free calcium and sulfate. The sulfate (SO4) attaches primarily to excess magnesium (Mg), aluminum (Al) and sodium (Na) in the soil complex, making soluble compounds that move down and out of the crop rooting environment. The remaining Ca from the gypsum then attaches to the exchange sites, replacing the excess Mg, Al, Na, etc. in the soil complex. This is what sets the stage for improved soil structure.
Calcium is a positively charged ion called a cation. Cations are absorbed by the plant roots and also held on exchange sites in soils. The positive charges of calcium are attracted to negative electrical charges found on the exchange sites on clay particles and Organic Matter (OM). The more clay and OM, the larger the attraction. This attraction of the positive Ca with negative charges in the clay particles -- binds the clay soil particles together so they become flocculated and resist dispersing and soil structure breakdown.
Reference: Hydrologic properties and leachate nutrient responses of soil columns collected from gypsum-treated fields Rebecca Tirado-Corbala´ *, Brian K. Slater, Warren A. Dick, Jerry Bigham, Edward McCoy.