Soybean growers across Illinois continue to ask whether sulfur applications can reliably deliver a yield bump. In 2025, our Illinois Soybean Association (ISA) On-Farm Trial Network tackled this question head-on by evaluating 16 locations that consisted of a wide range of soils, weather, and management practices. The short answer: sulfur yield response can be real — but it’s complicated. 

Why sulfur matters more today 

For decades, industrial emissions supplied Midwest soils with 10–30 lb./acre of sulfur through atmospheric deposition. After the 1970 Clean Air Act reduced sulfur dioxide emissions by over 95%, that free nutrient source essentially disappeared. 

Sulfur is essential for amino acid formation, nitrogen fixation, chlorophyll production, biomass growth, and seed quality. Soybeans take up about 85% of their sulfur during reproductive stages, making in season availability especially critical. 

Inside the 2025 sulfur trials 

This year’s sulfur trials included a minimum of 40-acre field scale layouts with replicated strips of spring applied sulfur (ATS or AMS) versus untreated checks. Each participating farmer contributed four years of management data and ISA collected soil samples, tissue tests, field insights, and yield monitor data. 

Across the state, results were mixed — and that variation is exactly what makes this dataset valuable. 

Where we saw yield response 

Counties including Bureau, Champaign, Knox, and Vermilion delivered the clearest sulfur responses in 2025, with yield bumps ranging from roughly 2 to 7 bushels per acre depending on sulfur form, soil type or texture, moisture, residue, cover crop, and soybean variety. Bureau County stood out with a +7.4 bu/A response attributed to sandy soils and lower organic matter. Champaign County also showed a positive +3.4 bu/A return with cover crops, higher residue, low rainfall, but with a high organic matter. 

Interestingly, planting dates and crop demand did not appear to play a role in sulfur response in 2025. 

Where sulfur did not pay 

Most sites showed little or no advantage with the addition of sulfur. These fields consisted of an average to very high application during 2024 and most of their 2025 spring soil tests showed adequate to high sulfur levels.  

Why responses vary 

• Sulfur form — AMS contains 24% sulfur in the sulfate (SO₄²⁻) which is immediately plant available. ATS consists of ½ sulfate and ½ elemental sulfur that needs to be oxidized to be available. 

• Soil type — Coarser soils (sand) tend to leach sulfate more quickly, but fine textured soils (loam, clay) typically contain more organic matter (OM) that holds more organic sulfur that must be microbially mineralized to sulfate. 

• Cover crops — Cereal rye can scavenge sulfate, but sulfur could be returned to the soil from residue. 

• Residue (C:N ratio) – high residue can temporarily tie up sulfur(S) during mineralization and N and S might be needed to feed microbes to aid mineralization. 

• Mineralization— Only 3–5 lb. of sulfur (S) per year are released for each 1% organic matter, and cool, dry soils slow mineralization. Waterlogging can cause anerobic conditions and some S can be lost as gas. 

Where we go next 

Our ISA On-Farm Trial Network will continue explore sulfur’s impact in Illinois in 2026. 

For now, sulfur isn’t a guaranteed yield booster — but with the right sulfur form, in certain soil and management conditions, with the right soybean variety and weather, it absolutely can be.