Experience Superior Sulfur Release With SO4

Sulfur is an essential component of plant growth, with key processes relying on sulfur like chlorophyll formation and protein production. It is often considered the fourth major nutrient behind N, P and K.

SO4 pelletized gypsum supplies a strong initial release of sulfur followed by a steady supply throughout the growing season, delivering the right of amount of sulfur to perfectly match plant needs for yield-maximizing plant growth. SO4 is mined and manufactured in northwest Iowa from one of the purest gypsum sources in the world. It is finely ground and pelletized to achieve a balance between solubility and pellet strength.

Why the Need for Sulfur is Increasing

Historically, much of the sulfur need was satisfied with atmospheric deposition as a result of coal burning industries. However, amendments to the Clean Air Act in 1990 targeted sulfur dioxide emissions, resulting in a dramatic decrease in atmospheric sulfur. Many areas of the central and eastern Midwest receive less than one half of the amount of sulfur today compared to 30 years ago.

Sulfate Ion Wet Deposition, 1985

Sulfate Ion Wet Deposition, 2016

Comparing SO4 & Ammonium Sulfate (AMS)

Not all sulfur sources are created equal. To meet your crops’ needs, sulfur needs to be released at a steady rate throughout the growing season. Ammonium sulfate (AMS) is 300x more soluble than SO4, releasing sulfur too quickly, making it susceptible to leaching. Learn more about how SO4 and AMS compare.

Enjoy the Benefits of SO4

Increases Corn Yield by 15.4 bu/acre

A compilation of 67 trials across the Midwest shows SO4 on average increases corn yield by 15.4 bu/acre compared to no sulfur. View the trial data below for details.

Releases Sulfur to Match Plant Needs

SO4 supplies a balanced initial sulfur release and a steady supply throughout the growing season. AMS releases sulfur too quickly, and elemental sulfur releases sulfur too slowly, neither meeting the crop’s complete needs.

Spreads Easily

SO4’s consistent pellet size allows it to be blended and applied with other dry fertilizers, which means it doesn’t require a separate application. It can be applied pre-plant in the spring, in-season via top dress or post-harvest in the fall.

Will Not Acidify Soil

SO4 is pH neutral, meaning it will not acidify the soil like other sulfur sources. Proper soil pH maximizes a plant’s utilization of nutrients promoting good plant health and optimizing yield.

Read Our Research Brief

A key finding from the study conducted determined SO4 supplies the best balance of initial sulfur release and steady supply throughout the growing season.

SO4 Trial Results

See the results of our SO4 yield trials in the Midwest and beyond.


Crop Type
Yield Goal (Bushels/A)
Sulfur (ppm)
% OM
Sulfur Recommendation (Units/A)
SO4 Recommendation (Lbs/A)

Hear from Our Happy Customers

“We use SO4 in some corn and soybean rotations for the sulfur source and get a little more calcium out there to help the plant grow… It’s easy to use. It’s readily available. ”

Pete Bonin

Agronomist, Premier Co-op

“Growers often mistake lack of sulfur for nitrogen deficiency, so we began pointing out the signs to our customers. Now almost all of my growers add sulfur to their corn.”

Roger Kenkel

Agronomy Manager, Aspinwall Cooperative; Aspinwall Iowa

“I used to see a lot of yellow spots in the corn fields, but now we don’t. It works!”

Joe Klein

Branch Manager, Farm Service Cooperative; Denison, IA

Start Using SO4 as Your Sulfur Fertilizer

If you are a grower interested in learning more about how to begin applying SO4 to your fields, use our locator to find the Calcium Products dealer in your area.

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