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Natural vs. Synthetic Gypsum

Synthetic Gypsum

What is Gypsum?
Gypsum is a mineral that has been used in agriculture for a long time. Its chemical name is calcium sulfate dihydrate (CaSO4 • 2H2O). It provides a sulfur source in the plant available form, sulfate, and provides calcium – both essential nutrients in crop production.

SO4 is naturally mined gypsum
SO4 is pelletized from gypsum that is naturally mined in northwest Iowa. Gypsum deposits were left behind when inland seas that used to cover Iowa dried up and receded.

Synthetic gypsum is a byproduct of burning coal
In contrast, synthetic gypsum (photo above) is a byproduct of burning coal. This source is commonly referred to as synthetic or flue gas desulfurized (FGD) gypsum. Power plants have ‘scrubbers’ that control emissions from their flue stacks. The process in its entirety is called flue gas desulfurization.

In short, these scrubbers filter by forcing sulfur dioxide and calcium carbonate (limestone) to react with one another, which creates calcium sulfite (CaSO3). Most power plants also use an additional step called ‘forced oxidation,’ whereby the calcium sulfite is oxidized to calcium sulfate, or synthetic gypsum. The resulting moist material is either landfilled or used in various industries around the U.S. – wallboard for instance. 

Challenges with synthetic gypsum
There are a few challenges with synthetic gypsum worth considering:
1. Coal contains heavy metals, which are generally isolated in the scrubbing process but occasionally can end up in the synthetic gypsum, raising obvious concerns about agricultural applications.
2. In bulk form, the material contains high moisture levels, making it difficult to spread and manage. As a result, recommended application rates are in the 1,000+ lbs/A range, which can create imbalance in the soil. These rates lack scientific evidence supporting their use in Midwest agriculture.
3. The purity of synthetic gypsum is only as good as the starting feedstock (limestone) and the system that produces it, creating highly variable chemical characteristics. Because of its synthetic/by-product nature, it will never be registered for organic use.

Synthetic gypsum is difficult and expensive to pelletize due to its fine particle size and requires the use of specialized binders and additives. This results in slow breakdown and activity in the field.

In summary, natural gypsum is mined from the earth while synthetic gypsum is a byproduct of burning coal. SO4 is pelletized, natural gypsum. It’s consistent pellet size allows it to blended and applied with other dry fertilizers.


ISA On-Farm Network Radio Spot

This year we have teamed up with the Iowa Soybean Association's On-Farm Network. They will be testing what effect sulfur has on crop yields.

Here is a short radio spot we did with them at their 2011 conference.

If you'd like more information about getting a trial on your farm

More on Sulfur

Yield Starts Here is a blog for farmers, focusing on increasing yield and profitability by focusing on the soil. It is managed by Craig Dick, a Blogronomist and Sales and Marketing Manager at Calcium Products. Find other articles by Craig and guest writers at .

Cost of sulfur, ammonium sulfate vs. calcium sulfate

While visiting with a dealer last week, I (Glen) discussed the attributes of different sulfur fertilizer sources.  The final choice between ammonium sulfate and calcium sulfate came down to the cost for a unit (#) of sulfate sulfur.  Here is what my calculations showed (these prices are not suggested to be indicative of every particular situation, but only an example):

Ammonium sulfate (AMS), 21-0-0-24S, was costing $0.75 per unit of sulfur (nitrogen value set to 0).

Calcium sulfate (SO4), 0-0-0-17S-22Ca, was costing $0.59 per unit of sulfur (calcium value set to 0).

If the sulfur requirement for 5 Ton alfalfa removal is 30# (6# sulfur per Ton), the cost for sulfur nutrition from AMS was $22.50 per acre, with the SO4 providing the same 30# of sulfur, but for a cost of $17.70 per acre.  Net difference (savings) to the grower of $4.80 per acre.

Not a huge difference, but still a 20% decrease in cost.  With the economic challenges of livestock production today, every little bit helps.

SuperCal SO4, the right fit, right now.



The Blogronomist is maintained by Craig Dick, head blogronomist and VP of Sales and Marketing. Here you will find a wide array of blog articles from Craig and expert guests on topics related to soil and crop health, farming, and so much more. If it’s not here, ask us!

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Maintained by our team of experts, we have a wide array of blog articles from our experts and guests on topics related to soil and crop health, farming and growing tips, and so much more. If it’s not here, ask us!

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