Gypsum provides plants with much needed calcium and sulfur by conditioning certain types of soil. When used on saline soils gypsum improves the soil structure, fertility and replaces salt content with calcium. This leads to healthier plants. According to Puyallup Research and Extension Center, PREC, with Washington State University, Gypsum effectively changes the structure and fertility of heavy clay soils as well. However, when applied to sandy or non-sodic soils gypsum can actually have a negative impact on plants and the soil system.
What is Gypsum
Gypsum is a sulfate mineral that is mined in a number of states including Oklahoma, Texas and Nevada. The School of Environmental and Natural Resources at Ohio State University states that, gypsum has been used in agriculture since early Greek and Roman times. Today gypsum is used primarily to manufacture sheet rock, plaster, cement, paint fillers and fertilizers. As a fertilizer gypsum offers plants an abundant supply of calcium and sulfur which are used to process other nutrients and produce protein to help plants grow.
Sodic soil refers to soils that are poorly drained and tend to crust on the upper-most layer of dirt. The Colorado State University Extension states that sodic soils often contain a high level of exchangeable sodium but low levels of total salt. This leads to toxicity in sodium sensitive plants as well as nutrient deficiencies in most plants. Gypsum is the most common form of calcium used to improve the soil content, CSUE states.
According to Fine Gardening, an online garden resource, some clay soils contain excessive sodium, similar to sodic soils. "The absorption of sodium by clay particles can cause aggregated clay particles to disperse or come apart, destroying friability and tilth," the web site states. The typical remedy for this is to apply gypsum in an attempt to displace the sodium content.
When to Use as Fertilizer
In addition to amending soil content gypsum can be applied directly to plants as a fertilizer. Plants suffering from a calcium or sulfur deficiency will generally have stunted growth, wilted or curled foliage as well as tip burn. Gypsum fertilizer can be applied either to the soil or directly on the plant.
Effects on Sandy and Non-Sodic Soils
According to PREC, gypsum can cause the leaching of phosphorus, copper and zinc in sandy soils as well as iron and magnesium when applied to acidic or non-sandy soils. This can cause stunted growth, root diseases and negative effects on plants and young trees.