Gypsum, chemically known as calcium sulfate (CaSO4), is well established as an effective soil amendment for treating clay soils, improving water filtration, providing a source of calcium, and more. More recently, however, gypsum is being recognized for its ability to also provide crops with a source of plant-available sulfur, a nutrient soils have become increasingly deficient in.
For this reason, along with the many other benefits associated with gypsum soil amendments, use of gypsum in agriculture continues to grow. And due to the many advantages offered by a granular product, pelletized gypsum is the best way to deliver it.
Benefits of Gypsum Pellets as a Source of Sulfur
Sulfur deficiencies in soils around the globe have become a growing problem in recent years due to a reduction in the amount of sulfur deposited from the atmosphere, as well as a few other factors impacting the amount of sulfur soils naturally hold. As a result, growers are finding that they need to supplement the sulfur in their soils to provide more balanced crop nutrition, and applying gypsum is one way to do that while also accruing other benefits.
Gypsum can supply around 18 percent sulfur, making it an excellent source of the nutrient. In selecting a source of sulfur, gypsum is frequently chosen for the following benefits:
Gypsum Won’t Modify Soil pH
Unlike some other forms of sulfur that can increase soil acidity, gypsum is neutral and therefore will not modify pH, allowing growers to incorporate sulfur into their soils without having to worry about altering the pH.
Gypsum Provides an Optimal Release of Sulfur
While the sulfate in gypsum supplies an initial boost to plant-available sulfur, it is not as soluble as some other forms of sulfur such as ammonium sulfate, providing a slower release after the initial boost. Research has shown that depending on the rate at which it is applied, the gypsum-supplied sulfur may even provide sufficient sulfur for multiple growing seasons.
At the same time, the sulfate in gypsum provides a quicker release than elemental sulfur, which is often too slow for practical needs, so farmers can count on near-term results.
(Natural) Gypsum is an Organic Source of Sulfur
Natural gypsum is considered organic by the Organic Materials Review Institute, serving as an organic source of sulfur. Note that synthetic gypsum does not fall under this category.
Gypsum Provides an Array of Benefits to Soil
In addition to providing a source of plant-available sulfur, gypsum also supplies calcium, plus a host of other benefits, including natural aeration, improved soil structure and reduced erosion, better water infiltration, reduced runoff, and more.
Sources of Gypsum
Gypsum for use as a soil amendment may be obtained through three primary sources:
Natural Gypsum
Natural gypsum is mined all over the United States and the world. Gypsum mined from quarries and underground mines is crushed and if needed, processed in a gypsum dryer.
Synthetic Gypsum
Synthetic gypsum, or syn gyp, generally refers to FGD gypsum, or gypsum produced in the flue gas desulfurization process, though other forms of synthetic gypsum do exist. Synthetic gypsum from flue gas desulfurization is produced at coal-fired power plants, where scrubbers remove sulfur from emissions prior to atmospheric release.
Recycled Gypsum
Gypsum is infinitely recyclable, making it a highly sustainable material. Recycled gypsum can come from a variety of sources, but the largest stream of gypsum waste by far comes from the uninstalled wallboard and wallboard scraps found at construction sites.
Raw Gypsum vs. Gypsum Pellets
While raw (crushed or powdered) gypsum can in theory provide the same benefits as pelletized gypsum, by converting gypsum to a granular form, growers are able to better realize the value of their gypsum. Some of the key benefits pelletized gypsum offers include:
Improved Handling
Pellets are much easier to handle, store, transport, and apply than crushed or powdered gypsum. This is primarily because raw gypsum is incredibly dusty, making any sort of handling or transfer messy and unpleasant. Powdered gypsum also has a greater potential to clump together, clogging equipment and increasing housekeeping and maintenance requirements.
Better Application
Also because raw gypsum is dusty, gypsum applied on fields often becomes windblown (sometimes before it even hits the soil). This results in unpredictable results; areas where gypsum was applied may not receive the proper amount, while other areas not intended for application (or neighbors) receive the gypsum.
Application in itself also becomes easier, as pellets are inherently more flowable than powder, allowing for precise and controlled metering. Pellets also move easily through standard spreading equipment.
Reduced Product Loss
In addition to being difficult to handle and apply, crushed gypsum can also result in a significant amount of product loss because of the amount of dust generated and discarded. By pelletizing gypsum, product loss is substantially reduced.
Producing Gypsum Pellets
Gypsum responds readily to wet granulation, a type of agglomeration often referred to as pelletizing. The gypsum pelletizing process typically employs a pin mixer, disc pelletizer, and rotary dryer, as well as some ancillary equipment. On a high level, the process can be described as such: gypsum powder and the chosen binder are blended into a homogeneous mixture in the pin mixer, where seed pellets begin to form.
The seed pellets and additional fines are fed to the disc pelletizer, along with additional binder, which causes the seed pellets to pick up additional fines, creating a layering effect known as coalescence that essentially “grows” the pellets.
Once pellets have reached the desired size, they are discharged from the disc pelletizer and fed to a rotary dryer, which brings pellets down to the target moisture content. Oversize and under-size pellets are screened out and returned to the process through a recycle loop.
For a more in-depth explanation of this process and the equipment used, see our article with infographic, Processing Gypsum for Use in Soil Amendments.
Incorporating Gypsum into Specialty Fertilizers
In addition to producing gypsum as a stand-alone soil amendment, which may be applied singularly, or blended with other amendments and nutrients, gypsum may also be incorporated into the formula of specialty fertilizer products; gypsum can be included as an additive during the granulation process and may even help to facilitate granule formation in some cases.
Gypsum Pelletizing Process Development
Whether gypsum will be pelletized on its own or incorporated into a more comprehensive formulation, process development testing such as that offered by the FEECO Innovation Center is often a necessity; while gypsum responds well to agglomeration, the variation that exists between different sources of gypsum makes knowing exactly how it will respond difficult to predict.
Testing is used to work out the process parameters required to produce a product with the desired specifications. These process parameters can be manipulated to target specific particle characteristics such as:
- Bulk density
- Attrition
- Crush strength
- Moisture content
- Solubility
- Particle size distribution
- And more…
Conclusion
Gypsum pellets provide a valuable source of plant-available sulfur when used as a soil amendment. As a source of sulfur, gypsum won’t modify soil pH, provides an optimal release rate, and can serve as an organic source of sulfur, among the already well-established benefits it provides to soils. Gypsum may be derived naturally from mining, synthetically as a process by-product, or recycled from the construction industry (or elsewhere) and performs best in the form of a pellet. Due to the wide variation in gypsum sources, testing is often necessary to work out the process parameters required to produce the desired results from the specific source of gypsum at hand.
FEECO is the leading provider of custom gypsum granulation equipment and systems for the production of premium gypsum soil amendments and specialty fertilizers. Process development services are also available through the FEECO Innovation Center. For more information on our custom equipment or testing services, contact us today!