Sulfur in Soybeans Conversation Guide

Sulfur plays an important role in soybean production. However, growers may have questions about why this vital nutrient needs to be included in their fertilizer plans. The following conversation guide can be used to help answer some common questions your growers may have about sulfur. For a printable version, download the PDF here.

Why should I include sulfur in my fertilizer plans? 

• Sulfur is the fourth major nutrient crops need after N, P and K. 
• Sulfur is a necessary nutrient during the vegetative and reproductive stages of soybean growth.
  • It is essential for the synthesis of chlorophyll as well as sulfur-amino acids and proteins that are needed for plant growth.
• Sulfur is also required for root nodulation, which provides biological nitrogen fixation.
  • Nodules supply about half of the nitrogen used by an average soybean crop.

Won’t I be able to get enough sulfur for my crop from the atmosphere? 

• In previous decades, crops did receive most, if not all, sulfur needed for average yield potential from atmospheric deposits. 
• The Clean Air Act enforced stricter EPA emission regulations that reduced atmospheric sulfur depositions across the United States.
  • This change has amounted to 50%-80% less atmospheric sulfur available to crops (less than five pounds per acre). 
    • This has led to an increased need for supplemental sulfur application across many crops, including soybeans. 

What are my sulfur options? 

• Two common sulfur sources are ammonium sulfate (AMS) and elemental sulfur (S). 
• The form of sulfur makes a difference in what is actually available to the plant roots to absorb. 
  • Sulfate is the only form of sulfur that plant roots are able to take up.

 What are the differences between elemental sulfur and AMS? 

• Granular ammonium sulfate (AMS) is a dry granular fertilizer containing 21% ammonium-N and 24% sulfate-S. 
  • AMS is highly soluble in water and readily available, so it immediately delivers sulfate sulfur to the plant roots as it dissolves in the soil. 
    • It can be used to correct in-season deficiencies. 
• Granular elemental sulfur (S) may be in the form of dry elemental sulfur with bentonite or as a co-granulated sulfur product.
  • Elemental S is water-insoluble and must be oxidized by soil microbes into sulfate before it can become available to be used by the plants. 

Can I afford to include AMS in my fertilizer plans? Will I see a return on my investment? 

• AMS is a cost-effective fertilizer. 
  • Most growers who use it on soybeans see a positive ROI from yield increases of 2-3 bu/ac. 

Are there any trials to support that AMS works? 

• AdvanSix conducts real-world, on-farm trials of AMS on soybeans through its Supplement Your Soybeans program. 
  • Over the past four years, growers have seen an average yield advantage of 3.75 bu/ac on AMS-treated acres compared to the untreated acres.

When and how do I apply AMS for soybeans? 

• Ammonium sulfate has flexible application options. 
• With readily available sulfate sulfur and ammonium nitrogen, there are a few different opportunities to apply AMS throughout the growing season.
  • When applied within two to three weeks of planting, from pre-plant all the way to V4/V5, AMS can help jump-start the crop by supporting early-season growth and healthy nodulation.
    • Since soybeans can’t make their own nitrogen until the V3 stage, the early AMS application can also provide the nitrogen the plant needs for early growth, before nodules are ready to fix atmospheric nitrogen.
    • Additionally, when applied during this time frame, AMS can also help unlock phosphorus and micronutrients like boron, zinc and manganese – enabling plants to absorb these nutrients along with sulfur and nitrogen.
  • AMS can also be topdressed around bloom or early reproductive stages to support the key plant reproductive stages. 
    • Taking into consideration that half of the nitrogen and sulfur in the soybean grain is taken up after flowering, topdressing can be a way to ensure sulfur is not lacking.  
      • Given that sulfur is relatively immobile within plant tissues, it mostly needs to get to the developing pods via roots from the soil. 

How do I know how much AMS to apply? 

1.  Determine your yield goals and the nutrient requirements of the crop to reach them.
2.  Use your soil tests to determine what may be available from the soil.
3.  Calculate your sulfur and nitrogen needs for the upcoming season to determine how much AMS you need to apply.
4. In-season, you can also conduct tissue testing to see if a deficiency exists. There may be an opportunity to address sulfur and/or nitrogen deficiencies with AMS.
   

How does AMS support early-planted soybeans? 

• Planting earlier means planting into cooler soils. 
  • This also means that organic matter mineralization is slow at best and therefore unable to provide any significant amount of plant-available sulfur or nitrogen. 
  • The plant will need to be supplied with readily available nutrients another way.
• When AMS is applied around planting, it feeds the crop both nitrogen and sulfur to give soybeans a jump-start to the season. 

I’m still on the fence. I’m not sure if AMS is right for my soybeans.

• Give it a try with a split-field trial through the Supplement Your Soybeans program and see what happens. 
  • Looking for an even lower commitment?
    • You could also try applying just one strip of AMS to your field and see if there is a difference in yields and/or plant health.

Where can I learn more? 

• Visit soybeans.advansix.com. 

For more tips on helping your customers learn how Sulf-N® ammonium sulfate can help them reach their goals, contact your AdvanSix Plant Nutrient Sales Rep.