Gypsum (CaSO4 • 2H2O) is a soft mineral that often appears in nature in crystalized formations and masses called selenite. Alabaster is a very fine white grain or tinted gypsum used in ornamental works. Today, farmers use co-product gypsum that is a readily available and consistently pure, soluble form of calcium sulfate dihydrate.
The benefits of applying gypsum to agricultural soils were established more than 200 years ago. Ben Franklin is often cited for having recognized the beneficial effects of gypsum or “land plaster” to his crops. Thomas Jefferson also reportedly used gypsum on his farm fields. But because gypsum was expensive to mine and transport the practice was lost, except in certain specialty crops, such as peanuts and potatoes.
Now GYPSOIL® is a better and much more economical source of gypsum.
GYPSOIL brand gypsum has the exact same chemical composition as mined gypsum but it is typically more pure than mined gypsum. GYPSOIL is a co-product of the process that cleans the air from coal-fired plants and is sometimes called FGD gypsum. GYPSOIL is also made as a co-product of certain processing plants for food-grade products.
The Clean Air Act Amendments of 1990 gave rise to new scrubbing systems used by many coal-fired utilities to remove sulfur dioxide (SO2) from their emissions. These scrubbers produce high-quality and very pure FGD gypsum.
The scrubbers create gypsum via a wet process that first forms calcium sulfite (CaSO₃ • 0.5H₂O) which is then oxidized into gypsum (CaSO4 • 2H₂O) and dried. The resulting material is ideal for land application because it is consistent and free of debris or impurities.
Gypsum is unlike other bulk-applied materials and so it requires the operator to understand a few basic things about handling it. It isn’t difficult to apply once you learn these basics and how to set up your spreader.
People often make the mistake of thinking of gypsum as an alternative to liming. Gypsum is not a liming agent even though it contains calcium. It does not affect the pH of the soil. It will not acidify soils like some other sulfur sources.
Proper pH is important in improving soil quality. If pH is too high or too low, nutrients are not as available and biological activities are not as efficient. Growers still need to correct any pH issues with appropriate levels of lime.
GYPSOIL is more soluble in water than lime (about 2.5 grams per liter) so the calcium in GYPSOIL is more mobile than the calcium in lime and so it moves easily deep into the soil profile.
For soils with highly acidic subsoils, GYPSOIL can help eliminate the toxicity that is associated with high levels of exchangeable aluminum (Al3). Generally, the lower the soil pH, the greater the concentration of soluble and available aluminum. For many plants growing in acid soils, the high levels of exchangeable aluminum prevent roots from flourishing.
Soil scientists at Ohio State University have completed a comprehensive field guide on the use and benefits of gypsum. To learn more click here.