Sulfur in Soybeans: What We Learned from the 2025 ISA On-Farm Trial Network

Feb 04, 2026

By Stephanie Porter

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.

Click here to see more...

Video: Spring 2026 weather outlook for Wisconsin; What an early-arriving El Niño could mean

Northeast Wisconsin is a small corner of the world, but our weather is still affected by what happens across the globe.

That includes in the equatorial Pacific, where changes between El Niño and La Niña play a role in the weather here -- and boy, have there been some abrupt changes as of late.

El Niño and La Niña are the two phases of what is collectively known as the El Niño Southern Oscillation, or ENSO for short. These are the swings back and forth from unusually warm to unusually cold sea surface temperatures in the Pacific Ocean along the equator.

Since this past September, we have been in a weak La Niña, which means water temperatures near the Eastern Pacific equator have been cooler than usual. That's where we're at right now.

Even last fall, the long-term outlook suggested a return to neutral conditions by spring and potentially El Niño conditions by summer.

But there are some signs this may be happening faster than usual, which could accelerate the onset of El Niño.

Over the last few weeks, unusually strong bursts of westerly winds farther west in the Pacific -- where sea surface temperatures are warmer than average -- have been observed. There is a chance that this could accelerate the warming of those eastern Pacific waters and potentially push us into El Niño sooner than usual.

If we do enter El Nino by spring -- which we'll define as the period of March, April and May -- there are some long-term correlations with our weather here in Northeast Wisconsin.

Looking at a map of anomalously warm weather, most of the upper Great Lakes doesn't show a strong correlation, but in general, the northern tiers of the United States do tend to lean to that direction.

The stronger correlation is with precipitation. El Niño conditions in spring have historically come with a higher risk of very dry weather over that time frame, so this will definitely be a transition we'll have to watch closely as we move out of winter.