Note: Learn more from Joe Ailts during his upcoming session at the 2026 National Strip-Tillage Conference, Aug. 6 in Springfield, Ill. 

While too small to see with the naked eye, microbial good guys establish a highly complex underground network of spider-web-like filaments that connect plant root tips with areas of the soil profile that the roots cannot reach. 

In fact, it has been reported that a teaspoon of soil can have 1-8 miles of arbuscular mycorrhizal filaments (AMF). Wrap your head around that. Miles of pipeline in a teaspoon. It’s almost too much to comprehend. 

Native prairie soils and undisturbed woodlands lean toward the 8-mile number, whereas ag soils typically have much smaller numbers of AMF. 

Chipping away at the complexities of the Haney soil test within a corn root, along with the microscopic fungal file-health test, has been quite an adventure with 3 years and over 200 filaments branching off to either side of the root.

Later samples characterized by three very disparate moisture growing seasons, has provided insights that reveal this test may help us do a much better job in guiding sidedress nitrogen applications. On the product side, I’m excited about dialing in the use of various plant growth regulators at specific growth stages to drive branching (in soybeans) and grain fill (in all crops). The future looks really bright.

Tillage Reduces Underground Microbes

Because this microbe creates long-lasting underground webs, it’s obvious to see how modern agricultural practices like tillage can disrupt this network. AMF are considered “obligant sybmionts.” which is scientific speak for “must be attached to a living root to thrive.” 

Ground that lays fallow does nothing to support populations of this microbe. In fact, “fallow syndrome.” commonly thought of as an early-season phosphorus deficiency in corn following fallow is actually not due to phosphorus at all. Instead, it is actually due to low AMF populations. Even with yearly crops, strong data shows fields tend to be quite low in AMF populations (we can pretty easily measure the presence or lack thereof of this organism).

Hopefully, you can see why I’ve targeted this bug as the lowest hanging fruit on the biological product tree. Farming practices that favor soil health systems such as no-tilling, strip-tilling, minimizing tillage, using cover crops, etc. tend to enhance native populations of these microbes.

For growers who may not be adopting those practices, it is possible to introduce AMF through dry seed treatments. This is the exact concept that I have been exploring the last 4 years as an independent agronomist. The results are very encouraging. I can say with confidence that using the right AMF product and in the right environment, can result in positive ROI harvests.

Before sharing examples of where this idea has worked, I want to share where I’ve learned it doesn’t work. I applied for and received a grant from the Wisconsin Department of Agriculture, Trade and Consumer Protection to explore the question, “Does AMF-treated corn impact nitrogen use efficiency?” 

Partnering with Huntsinger Farms in Eau Claire, Wis., we established a 25-acre, 40-block replicated research design where a split planter of AMF was compared with untreated corn. Across this plot, five nitrogen rates were applied at planting and side dressing to determine if AMF would influence nitrogen efficiency.

After crunching all the weighed yield data at harvest, I found a -1.9% yield response in the myco-treated corn vs. untreated across all nitrogen rates. This was the best-designed, most robust AMF trial I’ve ever conducted and I see it as representing the pinnacle work of my agronomy career.

My ongoing investigation into the one “biological” is one that I believe has the potential to bring significant yield advantage to nearly every crop we grow here in the north. Exploring the use of arbuscular mycorrhizal fungi (AMF) as a dry seed inoculant has been the pinnacle of my on-farm research endeavors. This microbe has fascinated me for over 25 years, as I’ve stated repeatedly that I believe this beneficial fungus is one of the most important species on the planet.

Quick Refresher

Nearly all plants on Earth (notably grasses) create a mutually beneficial relationship with this fungus. Once established, plant roots feed sugar to AMF. In return, AMF explore the far reaches of the soil profile and supplies root tips with water, nutrients and other plant defensive goodies. 

In doing so, the reach of a plant root system can increase by 10-100,000  times. AMF are also the primary microbe responsible for releasing glomalin, the glue that holds soil aggregate particles together. Further, these good guys help plants defend against root borne pathogens.

Almost sound too good to be true? Imagine buying a fertilizer product that supplies your crops with water, nutrients and a plant protection defense all in one package. However, science has identified that in the presence of high soil phosphorus, AMF-plant root associations are highly diminished. It is as if the plant knows there’s a buffet loaded with food in its root zone and therefore doesn’t need the “DoorDash” service that AMF provides. 

Sure enough, soil test phosphorus levels in his field were high enough to imply that a lack of response in this trial was to be expected. To further corroborate the results of this experiment, root samples of treated and untreated corn plants were sent analyzed for AMF root inoculation. These results helped explain the outcome, as neither sets of roots showed any meaningful AMF levels. We’ll try again this year in a low phosphorus field.

I believe an AMF inoculant does not work on high soil phosphorus fields, as this is what the science says and now I’ve seen it firsthand. However, I believe it provides meaningful responses on low phosphorus fields. 

Over the years, I’ve documented numerous split planter trials where the AMF result is indisputable. I was present when a 17-bushel difference in corn yield was weighed on a low organic matter, low soil in Wisconsin’s Dunn county. That’s not a typo as it was a legitimate 17-bushel per ace response. 

I found a similar response with historically-fumigated potato ground. Here again, low organic matter and low soil biology meant the opportunity for a significant response was there in the soil.

AMF Can Inoculate Fungicide-Treated Seed Corn

At this point, an acute observer may ask, “how can you get a beneficial fungus to grow on seed treated with fungicide?” It turns out that not all fungicides are fungal sledge hammers. Many are designed to target a specific class of fungus that may not have much in common with AMF.

Wanting to prove this concept, years ago I sent treated corn seed inoculated with AMF to a lab and had them grow the plants and test for colonization. The results definitively showed AMF can inoculate the fungicide-treated corn seed.

This journey has been fraught with a number of challenges that have served as learning opportunities. AMF as a seed treatment sounds simple on the surface, but there’s a mountain of nuance that goes along with this practice to get it right. Product selection is essential as most products on the market have too low a dose of the live bug to make a difference and nearly all are dead on arrival. There’s no regulation in this industry regarding AMF quality and companies can sell you dead bugs. 

Having worked through these challenges, my summary of responses over the years show a 5–7-bushel average gain in corn and a 4-6-bushel average yield gain in soybeans. It costs less than $12 per acre to apply a potent, quality product. That math leads to decent ROI.

I’m not trying to sell a product, but I am trying to sell farmers on an idea If you can sift through all the garbage in today’s ag biologicals space, there are products and concepts that have legitimate merit. I encourage you to set up research on your farm and figure out what works, because with a little effort, there’s stuff that can bring pretty exciting responses.