How do ammonium sulfate and gypsum differ? | AdvanSix Ammonium Sulfate

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AdvanSix’s agronomy experts are available to answer your questions about how to get the most out of your ammonium sulfate investment. Mercedes Gearhart has overseen agronomic research at AdvanSix for more than 20 years, and has a wealth of knowledge about fertilizer use efficiency and improving crop yields. Check out the questions asked below or ask your own question.

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How do ammonium sulfate and gypsum differ?
While both materials contain 100% sulfate sulfur, there are key differences:

One is largely a fertilizer, and the other is largely a soil amendment.

Sulf-N® ammonium sulfate is an established fertilizer in U.S. crop production, used for more than 60 years to supplement plant nutrition with readily-available forms of sulfur and nitrogen. Gypsum has historically been used in crop production as a soil amendment, where calcium is needed to reclaim sodic soils.

One provides nitrogen, and the other provides calcium.

Sulf-N ammonium sulfate is a readily-available source of sulfur that also supplies 21 units of nitrogen in the highly-stable ammonium form. Nitrogen and sulfur are the building blocks of protein, and work closely in the plant to support photosynthesis. Gypsum, on the other hand, supplies sulfur and calcium. Unlike nitrogen, which is critically needed in the majority of crop-producing soils, calcium is an element that most soils can supply in quantities that are more than enough for optimum crop yield.

One is highly soluble, and the other is slightly soluble. 

While Sulf-N ammonium sulfate is highly soluble, gypsum is only slightly soluble, so sizing becomes critical.

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Ammonium sulfate is more efficient to spread.

Sulf-N ammonium sulfate offers 45 units of total plant food, which makes more efficient use of your fertilizer bins. It is available in three grades to suit your business model:
  • Granular grade for high-quality bulk blending
  • Mid-grade for direct application
  • Fluid grade for dissolving into solution
Ammonium sulfate provides double the plant nutrition. 

With 24 units of sulfate sulfur and 21 units of ammonium nitrogen, Sulf-N ammonium sulfate is a high-analysis fertilizer offering 45 units of essential plant nutrition in every 100 pounds of product. Gypsum, by contrast, contains only 17 units of sulfate sulfur. The rest of the nutrient analysis – 22 percent – is calcium. As a result, gypsum can be considered a low-analysis fertilizer on the majority of crop acres, with calcium serving as “filler” and having little impact on crop yield.  

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