Agronomic and Environmental Benefits of Gypsum.

Gypsum has been used to improve soils and crop growth for over 2000 years. The ancient Greeks followed by the Romans were the first to use gypsum in agriculture but the practice was then abandoned when these Empires declined. It was resuscitated in the middle of the 18^th Century in Europe and North America where it was extensively used as a soil amendment, being promoted by Ben Franklin who had been impressed by its benefits on a trip to France. However its mode of action was unclear. In the 1930s the establishment of the US Salinity Laboratory introduced science into gypsum use and demonstrated its benefits in reclaiming sodic soils. Subsequently as a result of considerable research in Australia, Brazil, South Africa and the United States, gypsum use on soils expanded to cover topics such as the supply of calcium and sulfur as nutrients for crops such as peanuts, apples and tomatoes, and the improvement of soil physical and chemical properties promoted by clay flocculation such as the amelioration of soil crusting and improvement in infiltration, improved internal soil hydraulic conductivity, reduction in penetration resistance of subsoil hardpans, and mitigation of subsoil acidity. The resulting improved soil properties usually allow roots to penetrate deeper into the subsoil where they can access water previously out of their reach thus avoiding drought stress. The chronology of these improvements will be presented and discussed with illustrations to demonstrate gypsum efficacy in all these areas.