Calcium sulfate is ground into particles for agricultural application, with different particle sizes tailored to the different methods of application. The dissolving speed of calcium sulfate products depends greatly on the size of the particles. Finer particles dissolve more quickly than coarser particles because, pound-for-pound, fine particles present more surface area, which gives water more access to dissolve the particle.

Dry calcium sulfate is commonly spread from a truck, using a grind known as “ag fines.” A typical product such as Arcosa Specialty Materials’ Cal-CM + Agricultural Grade Calcium Sulfate is made of relatively small particles—ranging from 1/8” down to fines—and designed to dissolve and enter the soil gradually, during repeated irrigations.

Dust from ag fines can cling to some types of crops such as lettuce, which would be undesirable. For those crops, or for applications adjacent to such a crop, or anywhere else where drifting calcium sulfate dust would be a problem—a golf course, for example—there are pelletized or “prilled” products that fall more readily to the ground, where they can dissolve. In addition to agricultural applications prilled products are often used for lawns and residential gardening.

Prilled products can be made with very finely-ground materials for more rapid dissolving. For example, Art Wilson Cal-CM + Mini Prilled Calcium Sulfate ranges from 100-mesh to 325 mesh, with more than 50% of the product in the high end of that range.