The mineral gypsum is a byproduct of sulfide oxidation and is known as hydrous calcium sulfate or selenite. Mined worldwide, gypsum is found in shale beds, according to the Mineral Information Institute. Gypsum is an excellent source of calcium and is heavily used as an agricultural soil amendment.
Improves Soil Structure
Gypsum penetrates the particles in heavy soils or the layer of hard subsoil and serves to loosen the structure. In doing so, air and moisture are able to work their way into the mix and further break up soil structure. A neutral base, the mineral counteracts acidity by replacing aluminum and other acid-forming ions, allowing roots to successfully penetrate previously stiff soil.
Gypsum contains two of the 13 nutrients vital to plant growth--calcium and sulfur. While these nutrients are delivered with an application of gypsum, it is important to remember that gypsum is not a fertilizer and should be used in addition to a proper fertilization program. Organic and non-toxic, there is no danger of burning your lawn or plants with an accidental over-application.
Improves Fruit Quality
USA Gypsum, a gypsum refiner, promotes gypsum for fruit growth. Fruit trees require calcium, especially in developing trees, but the element is often just marginally sufficient in most soils. A slow mover, calcium does not always make it to all parts of the tree or vine. Supplementing the calcium with an application of gypsum not only helps fruit development, but it also stems off disease in peanuts and prevents blossom-end rot in watermelons and tomatoes.
Gypsum helps in water efficiency as it allows for deeper root penetration and increased leaching. Water hitting untreated compacted or clay soils will pool or run off, but after a long series of gypsum treatments, water is able to percolate down and keep soil moist longer.
Gypsum has generated a vigorous controversy in the horticulture/agriculture world. While heavily promoted by garden centers and the mining industry, there are many who feel gypsum offers few benefits to merit its purchase and the time spent applying the mineral. Linda Chalker-Scott, Ph.D, from Washington State University points out that, "urban soils are generally amalgamations of subsoils, native and non-native topsoils with high levels of organic and non-organic chemical additives . . . it is pointless to add yet more chemicals in the form of gypsum unless you need to increase soil calcium levels."