Do biostimulant seed treatments boost soybean yields? New study across 103 locations in 22 states says no

Biostimulants—especially seed-applied biological products—continue to generate interest across soybean-growing regions. The promise is appealing: improved early vigor, stress tolerance, or yield, often layered on top of existing seed treatments. But do these products actually deliver under real-world farming conditions?

A large, multi-state study led by Science for Success, a group of land-grant university soybean agronomists, set out to answer that question using an approach designed to mirror how farmers actually use these products. The study was published in the scientific journal Field Crops Research in December 2025.

Seth Naeve, one of the study’s 28 co-authors and a University of Minnesota Extension soybean agronomist, describes the goal clearly:

“We were really looking for which products worked in the most locations—and then trying to identify characteristics of environments products worked in—so that we could channel the use towards areas that would have a greater potential response or a better ROI.”

An applied, farmer-focused research approach

This study wasn’t designed to test whether biostimulants could work under idealized lab or greenhouse conditions. It was designed to test whether they work the way farmers are encouraged to use them.

The Science for Success group started by surveying farmers to understand which biological products were actually being marketed and used. From there, they built trials around those real-world products and practices.

“We used products as farmers would use them,” says Naeve.

Key features of the study design included:

• 8 to 10 commercial products tested per state
• A wide range of active ingredients, reflecting how companies often blend multiple biologicals in a single product
• A Base “Premium” fungicide/insecticide seed treatment (Bayer Acceleron) used at all locations, with biostimulants added on top—exactly how many farmers deploy these products
• Careful handling to give products every possible chance to succeed:
• Cold storage
• Seed treated the day before planting
• Uniform seed sources
• Trials placed in good, high-production environments representative of where farmers actually grow soybeans

As Naeve put it:

“We did our absolute best to get the best possible outcome from these products.”

The results: “Nothing worked anywhere”

Across 103 locations in 22 states, the results were remarkably consistent—and unexpected.

“The biggest surprise of anything is that nothing worked anywhere,” says Naeve. “Even among cynical people like me, that was really shocking.” 

Not “some products worked here and there.” Not “one product worked in certain regions.” But there was no consistent yield response across environments.

The only hint of a response came from Bradyrhizobium inoculants, which showed positive, statistically significant yield responses at a few locations—a result that aligns with decades of existing agronomic knowledge rather than new biostimulant claims.

Why this matters for farmers

This study doesn’t argue that biological products can never work. But it does show just how difficult it is for them to work reliably and predictably at field scale.

As Naeve explains:

“There’s a million ways where these things can go wrong, and everything has to go right for them to work.”

Some of the challenges include:

• Survival of living organisms during storage, handling, and seed coating
• Competition with native soil microbes
• Timing—especially whether early-season conditions truly limit soybean performance
• Environmental specificity that’s hard to predict in advance

What this study does—and doesn’t—tell us

What it tells us:

• Seed-applied biostimulants should not be expected to deliver consistent soybean yield increases.
• Broad marketing claims don’t hold up when tested across many environments.
• Farmers should be cautious about adopting these products at scale without local evidence.

What it doesn’t tell us:

• That biologicals will never work under any conditions
• That all future formulations will fail
• That non-yield benefits (e.g., stress mitigation in extreme years) will not be helpful in some environments.

But it does show the bar is very high for these products to succeed consistently.

“If we can put these out in 103 locations and we get virtually nothing, it really demonstrates the challenges we have with these types of products,” Naeve concluded.

Practical takeaways for farmers and advisers

• Test locally before scaling up. Small on-farm strips beat whole-farm adoption.
• Don’t expect yield insurance. These products are not a guaranteed return.
• Be realistic about risk vs. reward. Costs add up quickly when responses are inconsistent.
• Lean on proven agronomy first. Variety selection, planting date, drainage, fertility, and pest management still matter far more.

Bottom line

This was one of the most thorough, farmer-relevant evaluations of soybean biostimulant seed treatments to date. The researchers gave these products every reasonable opportunity to succeed—and they largely didn’t.

For now, the evidence suggests soybean biostimulants should be approached with caution, skepticism, and careful local testing, not as a plug-and-play yield solution.

This blog post was written with assistance from an AI language model and reviewed and edited by the author to ensure accuracy, clarity, and appropriate interpretation of the research.

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