Biologicals are booming across the agricultural landscape, propelled by a surge of new products and high-octane promises. Yet, when the invoice arrives, farmers are often left with this nagging question: Did I actually need that?
University of Illinois field researcher and assistant professor Connor Sible is on a mission to provide clarity. Drawing on a decade-plus of in-field study in corn and soybean systems, Sible offers a farmer-first filter to cut through the marketing noise. His research is helping growers determine where these tools offer a reliable return on investment — and where they fall flat.
“Start with your agronomy, then decide if a biological adds value on top,” he advises. “They’re not a shortcut around good fundamentals.”
One of the key reasons why farmers struggle to cut through the noise and identify which biological products will work for them results from the shear number of biological products in the marketplace. Another challenge is what this class of products is called. Academia and regulators use the term biostimulants. Ag media, companies and most farmers increasingly use the broader term biologicals.
The Baseline: Deliver on Fundamentals
For all the excitement surrounding biologicals, Sible encourages farmers to focus on unglamorous agronomic foundations first. He describes biologicals as next-step inputs; they can sharpen a high-performing cropping system, but they will not rescue one built on outdated practices.
“I do not know of a biostimulant or biological today that will fix your pH,” Sible says. “If you’ve got a soil pH issue, fix that first. Same with drainage, and same with using the same hybrid you’ve used for six years just because it’s still available.”
The Logistics: Is it Dead or Alive?
Once the fundamentals are solid, Sible says a practical next step is to consider whether a product is living or non-living.
Beneficial microbes — such as nitrogen-fixers, phosphorus-solubilizers, residue degraders, and many seed-applied inoculants — are alive. Many biostimulants — including humic and fulvic acids, certain enzymes, and kelp- or marine-based formulations — are not.
That distinction isn’t just academic; it determines whether a product has any chance of working by the time it reaches your field.
“If you’re buying something living, you’re buying a responsibility,” Sible says. “You have to keep it alive from delivery to application.”
He urges farmers to evaluate their shop conditions: Can you provide temperature stability? Is the product sitting against an uninsulated exterior wall? If the logistics of babysitting a living organism do not fit your management style, Sible suggests using only non-living biostimulants.
Nutrient Efficiency: Boosting Nitrogen
Few biological categories have generated as much buzz as nitrogen fixers. Sible’s work suggests they can play a role — but not the one many farmers might first imagine.
For a typical corn crop, about half the nitrogen comes from applied fertilizer and about half from soil organic matter and mineralization.
Biological N fixers are best thought of as a third source of nitrogen, he says, helping to cover shortfalls when fertilizer is lost or tied up, or soil mineralization doesn’t keep pace with crop demand.
From his data on a 230-bushel corn crop, the key number is 7 pounds of nitrogen per acre per day. That’s how much the plant must take up every day for about three weeks at peak demand. At 300 bushels, that jumps to around 9 pounds per acre per day. One of the questions farmers need to ask their retailer on a nitrogen-fixing biological they’re considering is, how much will it help provide during the key periods of demand?
Sible makes two critical points:
- Don’t cut N and expect a biological to fully replace it.
When growers drop early-season nitrogen in hopes that microbes will fill the gap, his team often sees corn respond by reducing kernel set. The yield ceiling falls before the biological has time to colonize and contribute. - Placement and mode of action matter.
Products marketed as N fixers don’t all work the same way. Some colonize roots externally, some live inside the plant as endophytes, and some may enhance N assimilation rather than truly fixing atmospheric N. That affects:- Whether they’re best applied in-furrow, on-seed or foliar.
- What they can be tank-mixed with.
- When they’ll begin supplying nitrogen.
Farmers trialing N-fixing products this season should treat them as insurance or a supplement and not a license to slash N rates across the board, Sible advises.
Phosphorus-Solubilizing Microbes
Soils often hold a high volume of total phosphorus, but much of it is locked in forms plants cannot access. Certain microbes can free up this nutrient by secreting weak organic acids that chelate soil cations away from phosphate.
In field trials, the most consistent benefits occurred when microbes were supplied in-furrow or very near the roots and applied alongside phosphorus fertilizer. Using “difference methods” to track uptake, Sible reports that baseline efficiencies often sat between 4% and 7%. With a P-solubilizing product, that jumped to the 7% to 11% range in some environments.
“It’s still not great, but it nearly doubled our efficiency in some environments,” he says. However, he cautions that cutting fertilizer back significantly and expecting microbes to “mine” the difference is not a reliable strategy.
The Carbon Battle: Residue Management
Residue degradation is where Sible sees some of the strongest opportunities for biologicals, especially in high-yield or no-till systems.
Every 10 bushels of corn adds about 440 pounds of residue; over a decade, a yield gain of 25 bushels can mean an extra half-ton of residue per acre.
The challenge is the high carbon-to-sulfur ratio in corn stalks, which ties up nutrients. Sible’s research has found that biological degraders are inconsistent on their own but show significant synergy when paired with nitrogen and sulfur.
“If you’re going to use these, understand they’re fighting an uphill battle against carbon,” Sible says.
He also stresses application timing: “Spray on cloudy days or in the evening to take advantage of overnight dew. You have to set the product up to succeed.”
Carbon and Humic Products
When evaluating humic acids and molasses-type products (sugar), Sible notes a clear divide between crops. In soybeans, results have been largely inconsistent. In corn, however, in-furrow carbon and humic products produced small but consistent yield gains that held up under economic analysis.
Sible attributes this to crop physiology. Corn makes major yield decisions twice: during early vegetative stages (kernel potential) and at pollination (kernel retention). Supporting the plant during these specific windows has offered a measurable response.
Soybeans, by contrast, adjust yield daily from flowering through seed fill, making them a much harder target for a single application of a biostimulant.
Stress-Mitigating Products
Sible sees value in some stress-mitigating products — often kelp or marine extracts — that claim to help crops tolerate drought, heat or other abiotic stress. He notes these materials are often rich in metabolites that help plants survive extreme fluctuations in temperature, moisture and salinity.
When applied to crop leaves, these materials can trigger stress-defense pathways.But they only work if they’re applied before the stress hits.
“You have to be proactive, not reactive,” Sible says. “If the corn is already curled or the soybean leaves are flipped over, it’s too late for these products to do much.”
He tells farmers to watch their 7- to 10-day forecasts and time applications ahead of expected heat waves or dry spells, adding that these products are ineffective as rescue treatments.
From Products to Purpose
Across all categories of biological products, Sible’s advice remains the same: define your “why.” If a product doesn’t clearly fit a specific goal — such as improving N efficiency at peak uptake or accelerating residue breakdown — it may not be worth the investment.
“There are some really exciting tools out there,” Sible says. “But the value comes when you use them precisely, not when you expect them to fix everything.”
As farmers evaluate biological products, Sible notes there are about 10 frequently used types of “active ingredients” that are better-understood, likely credible and worth evaluating. They include:
- Bacillus amyloliquefaciens
- Bacillus subtilis
- Bradyrhizobium spp. (classic soybean inoculant – “the original biological”)
- Azospirillum spp.
- Trichoderma spp.
- Azotobacter spp.
- Several other Bacillus and related species are in the top-10 list, as well.
Sible’s framing of these for farmers’ consideration:
If a new product contains one or more of these top 10 species, it “fits the larger narrative of this market.”
If it has something totally different, it might be:
— a random/unproven one-off, or
— truly novel and promising – but in that case he suggests being more cautious and asking more questions.
