The Sulfur Difference

Recent studies have shown sulfur deficiencies are widespread among alfalfa crops. Higher air quality standards, increased crop yields pulling more sulfur from the ground, and a greater use of low or sulfur-free nitrogen and phosphorus fertilizers have all contributed to the problem. Sulfur must be replaced to maintain plant health. And, for today’s grower there are two options when selecting a sulfur source, elemental sulfur (So), or sulfur in the sulfate form (SO4). Understanding the difference between the two (and how elemental sulfur oxidizes into sulfate sulfur) will help you make a choice that’s best for your crop, and ultimately your yield.

Sulfur in the sulfate form offers flexibility because the product is ready for plant uptake immediately. Elemental sulfur, on the other hand requires time to oxidize to the sulfate form. And for that to happen, the following factors must align.  

  • The soil must contain enough bacteria
  • The temperature should be between 75 and 105° F
  • Plenty of time should be allotted for the bacteria to convert the sulfur
  • The moisture level must be conducive
  • The sulfur needs to be very finely ground
  • The soil should have an acidic pH reading


Another factor to consider is the competition between the bacteria causing oxidation and plants’ root systems. Both need the same nutrients to survive. So, if oxidation is in full swing, the bacteria breaking down the elemental sulfur may also be robbing your root systems of nitrogen and other key nutrients. 

It’s important to note that if your crop is already exhibiting sulfur deficiencies, you don’t have the time to wait for sulfur to oxidize to the sulfate form. Immediate uptake is crucial. Gaging your crop’s need and taking into consideration the above factors will help you as you select your sulfur source.