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May 21, 2024

Smart Strategies for Mid-to-Late Season Sulfur

Insights on the “sulfur showdown” – AMS vs. elemental sulfur – show new opportunities to get the best results yet.

Today there is better awareness than ever that supporting your crop with season-long sulfur is critical to success. 

Sulfur fertilizer recommendations have increased due to greater deficiencies and variability, combined with recognition by experts that sulfur has become a standout difference maker – particularly for top cash crops from canola and corn to soybean and cereals. 

The two main categories of sulfur fertilizer sources have been sulfate fertilizer, such as ammonium sulfate fertilizer (AMS) and elemental sulfur, such as our Bentonite Elemental Sulfur products from Keg River. 

Both types of fertilizer have different qualities and advantages, and both can play an important role in your sulfur fertilizer strategy. 

The key difference is that AMS, as a sulfate fertilizer, provides sulfate immediately available for uptake and use by the plant. Elemental sulfur, on the other hand, is not immediately available. It requires the activity of soil microorganisms to convert the sulfur into sulfate, which is effective but takes longer. So, what is the best way to balance the use of these two options?

Tried and true

In recent years, the common practice has been to use AMS applied in the spring as a starter sulfur. This gives the crop excellent support right away during early growth stages, helping to ensure a strong start toward a strong finish come harvest time. The drawback is that AMS is very mobile and prone to leaching – so while it can work great for early growth stages it can be less reliable for mid-to-late season unless you perform another application at those later stages. 

However, during this same period, there has been a lot of growing interest and adoption of using elemental sulfur as a season-long sulfur source. For many years now, a popular strategy has been to apply both AMS and elemental sulfur in spring –  with AMS ensuring critical early season support and elemental sulfur, while slower out of the gate, making a season-long impact including supporting the mid-to-late season. In effect, the AMS application is utilized as an insurance policy, to furnish available sulfate for critical early stages until soil sulfur is built up to healthy levels by elemental sulfur. 

New option for mid-to-late season? Because elemental sulfur, particularly Bentonite Elemental Sulfur from Keg River, is typically more economical than AMS, the more your strategy is based on elemental sulfur the more “bang for your buck” you can expect.

Taking advantage of fall application

More recently, there has been a big shift in elemental sulfur strategies, where now the popular time to apply is during the fall. This works well to give the sulfur-to-sulfate conversion process a head start in early spring and also to break up the farm workload. 

Elemental sulfur from Keg River is manufactured as a sulfur-bentonite pastille that is compatible with various fertilizer blends. Once applied in the field, the bentonite clay component of the pastilles absorbs water and swells, resulting in the degradation of the pastilles to deliver fine, high surface area elemental sulfur particles to the soil, which can then be converted into plant-available sulfate by the soil microorganisms. 

With a fall broadcast, pastilles land on the surface where they are exposed to the rigors of mother nature (rain, wind, snow, freeze/thaw, etc.) This has the effect of blurring the feeding sites where pastilles land on the ground, causing some beneficial nutrient dispersion through the winter. Since elemental sulfur particles are insoluble, you can expect negligible nutrient loss over winter.

Finding the best balance: shifting more of the workload to elemental sulfur

As more knowledge and data build on strategies for AMS and elemental sulfur, it’s becoming clear that elemental sulfur can be relied on for a stronger role.

For example, agronomists have advised for a while now that when fall-applied elemental sulfur is used, this can reduce the amount of AMS starter sulfur needed the following spring.

Building on this, with regularly applied elemental sulfur, there can be enough sulfur reserve built up in the soil to greatly reduce or eliminate AMS application. (The timeline for this varies with elemental sulfur application rate and frequency. Soil testing can help verify your plan’s effectiveness.) 

For many agronomists and growers, this has been very welcome news. More science, commercial data and expert opinion have been built year after year, confirming that using a top-performing bentonite elemental sulfur is one of the most effective and affordable options to provide season-long sulfur.

AMS remains a great option for the early season until reserves are built up. After that, it’s possible with testing and advice from trusted advisors to shift completely to an elemental sulfur strategy.

Aside from cost, the key disadvantage of AMS is that it is very mobile and leaches easily. Because of this, spring-applied AMS alone may not be enough to provide mid-to-late season support. It’s become more clear now than ever that fall or spring-applied elemental sulfur, especially when done consistently each year,  is the best and most economical way to ensure mid-to-late season support –  eventually leading to the option of minimizing or eliminating the need for AMS use (Read our related blog Can Elemental Sulfur Replace AMS to Meet Immediate Crop Needs here.)


Available immediately in sulfate form that plants can utilize. As a result, AMS is utilized faster.


  • Effective soon after the application
  • Good option for early spring application (quick short-term impact)
  • Good top-up option for mid-to-late season application  (quick short-term impact)


  • Leaching risk 
  • Not recommended for fall application 
  • Typically less economical than elemental sulfur
  • High salt index
  • Storage and handling issues

Elemental sulfur

Must first be converted to sulfate by the activity of soil microorganisms. As a result, the impact is more delayed.


  • Slower release and conversion support steady season-long impact
  • Good option for fall application to provide early spring and season-long support
  • Typically more economical than AMS and reduces the need for AMS
  • Fall application saves time next spring
  • Elemental sulfur does not leach
  • New data showing advantages of additional mid-to-late season application option

Latest trend: New advantages with mid-to-late season ES application

Now, another key trend is further making the case for elemental sulfur options and flexibility. Data is building showing that a mid-to-late season application of elemental sulfur can bolster soil sulfur reserves to the point of both supporting the current crop and getting a further head start on supporting the next season’s crop.

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