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August 24, 2023

Can Elemental Sulfur Replace AMS to Meet Immediate Crop Needs?

In many crops, it’s standard practice to apply ammonium sulfate (AMS) at the start of the growing season while also putting down a degradable elemental sulfur (S) fertilizer as a season-long sulfur source. The two go hand-in-hand.

But did you know it’s also possible to eventually bank enough elemental sulfur in the soil to provide a continuous source of sulfate to crops? Eliminating or minimizing the need for AMS as an early sulfate source!

Crops require plant-available sulfate out of the gate…

AMS is a common choice as a starter sulfur in crops with a high sulfur demand. The reason is simple. AMS is a sulfate fertilizer. Sulfate (SO4-S) is immediately plant-available. It provides nutritional sulfur at the early growth stages, supporting plant functions such as starch and sugar synthesis, nitrogen metabolism chlorophyll production.

At 24% sulfate, AMS has a relatively high analysis compared to other sulfate fertilizers, with the added benefit of 21% nitrogen.

… and ongoing sulfate throughout the growing season.

The challenge with sulfate is that it’s highly mobile and prone to leaching in the soil. There is a risk that an AMS application will provide early nutrients yet may not stick around to meet the crops at later growth stages (ongoing chlorophyll production, protein synthesis and metabolism required for flowering and seed fill).

Elemental sulfur, on the other hand, is not mobile in the soil. It is slowly and steadily converted to sulfate by helpful microorganisms (microbes) in the soil – providing a steady, season-long source of sulfate.

Not only is elemental sulfur high analysis (85-90% S), but it’s also hugely economical.

A five-year plan to turn elemental S into your immediate sulfur source.

A funny thing happens with repeat applications of elemental sulfur.

Each year, the microbial populations keep growing. And growing. And growing. The higher the microbial population, the faster, earlier and more completely they can convert S to SO4-S. This in turn creates “a bank” of sulfate in the soil.

By the fifth year, the system can become self-sustaining: where there is enough sulfate in the soil to meet the demand at the earliest crop stages and throughout the growing season.

This process was demonstrated in research conducted in 2021, using data from America, Canada and Brazil. The authors found that after five consecutive years of elemental sulfur application, the yearly SO4-S supply was almost equal to the added sulfur rate.  

Soil testing can help verify the plan’s effectiveness by measuring soil sulfate levels as the program progresses.


After five consecutive years of elemental sulfur application, the yearly SO4-S supply was almost equal to the added sulfur rate.” 

A few things to know when applying degradable elemental sulfur.

Moisture is required to initiate breakdown: Degradable elemental sulfur is made with bentonite clay. When it gets wet, the clay expands to mechanically break the sulfur particles down into small pieces that the microbes can easily oxidize (1-180 microns). Premium-quality bentonite sulfur fertilizers perform vastly better than those made with mid-grade clay.

Fall application is recommended in winter climates: In parts of the US and Canada where crops aren’t grown over winter, it’s most effective to broadcast degradable sulfur post-harvest. Snow and moisture will expedite the mechanical breakdown for ready conversion in the spring.

Microbes are inactive in the cold: Microbial populations go dormant when temperatures drop. The optimum soil temperature is between 75°-105°F (24°-40°C). Oxidation of elemental S can only start once they become active again.

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