As thin margins and high fertilizer costs squeeze budgets, many corn and soybean growers are asking a hard question this spring: can biological products help out and pay their way in the field?
The answer depends on the goal, according to Connor Sible, University of Illinois field researcher and associate professor.
“Is the goal to get more out of what we’re already doing, enhance the yield in an already pretty intensive, progressive system?” he asks. “Or, are we trying to reduce inputs and then make up for that by maintaining yields with a biological?”
Sible studies high-yield corn and soybean systems and has spent years looking at how biologicals fit into real-world management. He says profitability hinges on getting a biological and a farming system to match. He offers two trains of thought on reaching a return-on-investment (ROI).
1. The Yield Response: Achieving a direct yield increase to offset the product cost.
2. The Efficiency Response: Improving nutrient uptake to maintain yields while reducing traditional inputs.
That framework for biological use underpinned the discussion during an Illinois Soybean Growers webinar on Tuesday: “Stretching Every Pound: Using Biologicals to Maximize Fertility During Input Shortages.” The program was hosted by the University of Illinois and Valent Biosciences.
Drew Harmon, Valent technical agronomist, provided an overview of row-crop farmers’ persistent struggles with accessing and covering the cost of fertilizer going into the 2026 season. He referenced recent American Farm Bureau and Bushel surveys showing the struggle underway across the Corn Belt and how the strain on farmers is changing their behavior.
“A lot of people are considering cutting their fertilizer by about 25%,” Harmon says. He reports that on his own farm, where soil tests are “on the higher end of a maintenance plan,” he and his tenant “decided to cut back our P and K by about a third this year.”
Cutting back fertilizer raises a practical question: how do crops still access enough nitrogen (N), phosphorus (P) and potassium (K) to perform and meet yield expectations?
One potential answer, Harmon and Sible say, is to use arbuscular mycorrhizal fungi, or AMF, especially where phosphorus rates are being reduced.
Harmon explains that mycorrhizal fungi are essentially a beneficial relationship that the fungi have with a host crop such as corn or soybeans. The root system supplies carbon through root exudates and, “in return for that carbon, the mycorrhizal fungi exchange nutrients and water.”
Applied as a seed treatment or in-furrow, AMF spores germinate in response to root exudates and colonize roots, then spread out as fine hyphae – branching, thread-like filaments – through the soil. That network effectively enlarges the rooting zone.
“Utilizing the mycorrhizal hyphae can expand the amount of surface area that [the crop] has to interact with, and it can expand that area by upwards of 50%,” Harmon says. “What that does is increase the opportunities for P and K uptake through diffusion, and it also allows greater access to soil water.”
In fields with lighter soils or facing recurring drought stress, that extended reach can be important. Even as much of the Midwest moves out of formal drought classification, according to the most recent U.S. Drought Monitor, Harmon notes that “we still can get those stretches of heat stress or stretches of flash drought… where we can see strain on our plants for needing water.”
Harmon also lays out an economic example for a typical two-year corn–soybean rotation under a biennial maintenance plan for phosphorus and potassium.
Using removal rates, yield estimates and recent DAP and potash prices, he calculates that a 25% reduction in P and K could offer “savings of mid-$40-ish per acre over a two-year period.”
The cost of using AMF in that scenario, he says, is about $6 per crop or just under $13 per acre over two years.
“AMF can be a potentially economical tool that could help increase nutrient uptake efficiency for the P and K that we’re reducing,” Harmon says, “while still protecting yield and preserving the majority of the fertilizer savings that you were looking to do.”
Harmon and Sible emphasize, however, that biologicals are not replacements for good agronomy—or for basic fertility.
“I don’t know a biological today that will fix a pH,” Sible says, as a for instance. “If we have a pH issue in the system, we probably need to resolve that before we go looking at new practices.”
A similar principle applies to nitrogen. Sible says nitrogen-fixing products can be useful as “a third source” of N, but they do not remove the need for a sound base rate.
“We often see an early-season biomass bump and higher kernel number potential [resulting from the biological product],” he says.
But to turn that into yield, the corn plant must have the nutrient resources to fill ears, which means adequate nitrogen and in-season management such as late fungicide use and/or supplemental nutrients.
For many farmers, another option this season for consideration is organic acids. Such products are positioned as biostimulants that support nutrient use efficiency, improve stress tolerance, and contribute to early growth.
Across both AMF and organic acids, Sible reminds growers that many biologicals are living tools, whether bacteria or fungi, and must be managed that way.
“A happy plant probably indicates happy microbes. Just like we need good conditions for plant growth, we need good conditions for microbial growth,” he says. “Plants need water, microbes need water. Plants need nutrients, microbes need nutrients.”
Harmon offers a similar caution on having the right set of expectations for using a biological.
“These products are not silver bullets,” he says. “They’re not fertilizer. They’re not going to [deliver] crazy amounts of yields. The majority of time you’re seeing it [improve] somewhere around 5% to 7% if you do see a biological response.”
