Micronized Sulfur Technology, Explained

Sulfur is widely recognized as an important component of a balanced crop nutrition program. Growers currently have options to apply sulfur as liquid or solid fertilizers, either in the form of sulfate, which is mobile in the soil, or elemental sulfur, which is immobile until it is oxidized. A newer option on the market for growers applying sulfur is Smart Nutrition™ MAP+MST®, a homogenous, co-granulated fertilizer product from Nutrien Premium Fertilizer Technologies utilizing Sulvaris’ micronized sulfur technology.

Sulvaris’ Eric Pedersen, Chief Science Officer and Executive Vice President of Research and Product Development, and Mark Howell, Agronomic Research and Development Manager, join us to explain this technology and how it can improve crop nutrition.

What is micronized sulfur technology?

Eric Pedersen: MST® stands for Micronized Sulfur Technology. The patented MST® process converts elemental sulfur, which is a byproduct of oil and gas processing, into ultra-fine (average particle size of <10 microns in diameter) elemental sulfur particles.  The technology also encompasses the co-granulation of these MST® particles with various NPK fertilizers to produce products like MAP+ MST®.

Why is the small particle size important?

Mark Howell: Pure elemental sulfur is inert, hydrophobic, and requires oxidation to sulfate before plants can utilize the sulfur. This process happens naturally as soil microorganisms oxidize the elemental sulfur into sulfate. But to do this, they need access to the surface of the elemental sulfur. If sulfur particles are large, the surface area exposed for oxidation is small, whereas when elemental sulfur particles are small like with MST®, there is a much larger surface area available to soil microbes. As you decrease particle size, the total surface area increases exponentially, which ultimately allows for more rapid conversion to sulfate.

How does MST® improve crop nutrition?

Mark Howell: MST® products provide an improvement to the elemental forms on the market, and can have benefits over sulfate forms. Since elemental sulfur oxidation is a biological process, the rate at which MST® is converted to sulfate is highly temperature dependent. When soils are cold the MST® remains in the elemental form. As temperatures warm, soil biological activity increases and starts converting the MST® to sulfate. This creates a ‘slow-release’ effect that coincides nicely with plant uptake requirements. In field trials in the U.S., we see that MST® products deliver an adequate supply of sulfur to crops whether applied in the fall or the spring before planting.  In these tests we always compare to equivalent sulfur rates of ammonium sulfate. We are also seeing that MST® can keep sulfur within reach of young roots that have not grown deep enough to access nutrients that may have leached lower in the soil profile, as is the case for sulfate fertilizers. Tissue samples taken in vegetative and reproductive plant growth stages also indicate that crop sulfur nutrition is maintained throughout the growing season.

Another important factor, especially when comparing to the 80-90% elemental sulfur products on the market, is that co-granulating MST® with other plant macronutrients allows for a more uniform distribution in the field since the sulfur is spread out amongst more granules.

Why was sulfur identified as the nutrient for this technology?

Eric Pedersen: Sulfur is one of the 17 essential nutrients required by plants to complete their lifecycle. It is a key component in the synthesis of protein, chlorophyll, and oil in plant tissue, and is essential for effective crop uptake of nitrogen. Sulfur is generally required in small amounts early in the growing season, large amounts during rapid vegetative growth and moderate amounts during grain filling. Sulfur can to some extent accumulate in plants but, unlike nitrogen, sulfur is relatively nonmobile within the plant – the primary reason why sulfur deficiency symptoms always occur at the top of the plant in the most recently developed leaves. Consequently, crops require a continuous supply of sulfate-sulfur from soil throughout their life cycle.

Sulfur fertilizer products composed of salt, like ammonium sulfate (AMS), are a great source of immediately available sulfur early in the growing season because they are fully soluble. The downside to salts is that in coarse soils they have a high risk of leaching during heavy or frequent rainfall events.  Elemental sulfur is not a salt and has very low solubility. The MST® particles stay in the soil where they are placed, and the sulfur only becomes mobile (soluble) as the particles are converted to sulfate-sulfur. The slow release of sulfate-sulfur from MST® results in more flexible application timing as it can be applied in fall or spring, higher sulfur use efficiency and reduced risk of environmental loss.

How does MST® help with seed safety when applying fertilizer with the seed?

Mark Howell: Salt index is a valuable tool for evaluating the relative salt potency of fertilizers. This is important because salts essentially compete for water with seeds.  So, if fertilizer with a high salt index is placed close to seeds, like with an in-furrow placement, it can delay or reduce plant emergence. Further to this, the nitrogen component of some fertilizers, like ammonium sulfate, can also be toxic to germinating seeds, which is why we have maximum recommended nitrogen rates for seed placed fertilizer.

With MST® products, the elemental sulfur component is not a salt so it does not contribute to the salt index. When applying it in-furrow, it is still important to follow the established recommended seed safe rates for a given operation. For example, in the case with MAP+MST, it still contains 9% nitrogen, so that needs to be factored in to in-furrow rate calculations.

Explain how Sulvaris identified the need for MST® in fertilizer.

Eric Pedersen: Sulvaris’ headquarters is in Alberta, Canada, so we have intimate knowledge of elemental sulfur as a byproduct of the oil and gas industry. We also understand that in agricultural soils, when nutrient outputs exceed nutrient inputs, the result is nutrient deficiency. This is the case for sulfur in much of the arable soils around the world. The cause of the reduced sulfur inputs is mainly from the success in implementing air pollution control technologies to remove sulfur dioxide from industrial emissions. Sulfur is no longer falling from the sky in the form of acid rain. At the same time, crop yields have been steadily increasing, a necessity for feeding our growing global population, but also resulting in greater nutrient (including sulfur) outputs. In many of our agricultural soils, sulfur outputs now exceed sulfur inputs and sulfur deficiencies are on the rise. According to Liebig’s Law of the Minimum, if we want to maintain high crop yield, we must address this sulfur deficiency by adding sulfur fertilizer. Using elemental sulfur from the oil and gas industry to address agricultural sulfur deficiencies has always been a large part of our company’s vision.


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