Gypsum is an element called calcium sulfate. It is used to loosen up stubborn, compacted or clay soils. Gypsum works by pulling together clay particles in the soil to make bigger particles, creating porous spaces for air, water and plant roots. For saline-infused soil, gypsum removes sodium and replaces it with calcium. For all soil types, gypsum adds calcium and sulphur, which are necessary elements for plant growth. Gypsum also helps soil retain water and helps decrease soil erosion.