Sources and Properties of Gypsum
Gypsum is a soluble source of the essential plant nutrients, calcium and sulfur, and can improve overall plant growth. Gypsum amendments can also improve the physical properties of some soils (especially heavy clay soils). Such amendments promote soil aggregation and thus can (1) help prevent dispersion of soil particles, (2) reduce surface crust formation, (3) promote seedling emergence, and (4) increase water infiltration rates and movement through the soil profile.
It can also reduce erosion losses of soils and nutrients and reduce concentrations of soluble phosphorus in surface water runoff. Chemical properties improved by application of gypsum include the mitigation of subsoil acidity and aluminum toxicity. This enhances deep rooting and the ability of plants to take up adequate supplies of water and nutrients during drought periods.
Gypsum is the most commonly used amendment for sodic soil reclamation and can also be included as a component in synthetic soils for nursery, greenhouse, and landscape use. These multiple uses of agricultural gypsum represent a great potential to provide benefits to agricultural and horticultural users.
Regular use of gypsum is essential to the sustainability of most irrigated soils. It has been used as a soil amendment and fertilizer for over 200 years. Gypsum is calcium sulfate. The most common form of it is the dehydrate which means that each molecule of calcium sulfate has two water molecules associated with it. It is expressed as 〖CaSO〗_4.2〖 H〗_2 O. The plaster of Paris used commercially has only one-half water and another form called gypsum anhydrite has no water. Much of the gypsum used in agriculture is mined and then pulverized to desirable particle sizes. The smaller sizes go into solution more rapidly than do large sizes. Gypsum is also a by-product of various manufacturing operations.