Arbuscular mycorrhizal fungi act as a powerful underground partner, extending plant roots and improving access to water and nutrients – in the right soil conditions

I believe that arbuscular mycorrhizal fungi (AMF) is one of the most important species on the planet.  

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 supply root tips with water, nutrients, and other plant defensive goodies. AMF are also the primary microbe responsible for releasing glomalin, the glue that holds soil aggregate particles together. 

All of that almost sounds too good to be true, eh? Imagine going to the fertilizer store and buying a product that supplies your crops with water, nutrients, and defense, all in one package. The Creator designed an amazing organism here.   

While too small to see with the naked eye, this microbial good guy establishes 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 one to eight miles of mycorrhizal filaments (hyphae) in it. Wrap your head around that — miles of pipeline in a teaspoon. It’s almost too much to comprehend. Native prairie soils and undisturbed woodlands will lean towards the eight-mile number, whereas ag soils typically have much smaller amounts of AMF. 

Because this microbe creates long lasting underground webs, it’s obvious how modern agricultural practices like tillage disrupt the network. Strong data shows that farm fields tend to be quite low in AMF populations (we can pretty easily measure the presence or lack thereof of this organism).   

You can see why I’ve targeted this microorganism as the lowest-hanging fruit on the biological product tree. Farming practices that favor soil health systems (minimizing tillage, incorporating cover crops, etc.) tend to enhance native populations of AMF. 

It is possible to introduce AMF in through dry seed treatments. I have been exploring this the past four years as an independent agronomist, and the results are very encouraging. I can say with a certain degree of confidence that using the right AMF product, 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 that 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, we established a 25-acre, 40-block research design where a split planter of AMF-treated vs untreated corn was planted. Across this plot, five unique nitrogen rates were applied at plant and sidedress to determine if AMF would influence nitrogen efficiency. 

After crunching all the weighed yield data at harvest, I found a -1.9 percent response in the myco-treated corn vs untreated across all the nitrogen rates. This was the best-designed, most robust AMF trial I’ve ever conducted, and the outcome was a big letdown.  

What happened? Science has identified that in the presence of high soil phosphorus, AMF-plant-root associations are highly diminished. It’s as if the plant knows there’s a buffet loaded with food in its root zone and it doesn’t need the “Door Dash” service that AMF provides. Sure enough, soil test P on this field was high enough to imply that the lack of response in this trial was to be expected. We’ll try again this year in a low-P field. 

I believe AMF inoculant does not work on high-soil-P fields. I believe it provides meaningful responses on low-P fields. Over the years, I’ve documented numerous split-planter trials where the AMF signature is indisputable. Of note, I was present when a 17-bushel difference was weighed on a low-organic-matter, low-P soil. I found a similar response on historically fumigated potato ground. All told, my summary of responses over the years implies a five- to seven-bushel average gain in corn and a four- to six-bushel average gain in soybeans.  

I’m not trying to sell a product. I don’t sell products, but I am trying to sell you on an idea: that if you can sift through all the hype in this ag-biological space, there are products and concepts that have legitimate merit. AMF as a seed inoculant is one of the practices that I believe has the brightest future. 

Lastly if the concept of mycorrhizal fungi captures your interest, I recommend reading Mycorrhizal Planet by Michael Phillips. It’s a great book written for the non-scientist that will leave you believing that AMF might just be some of the most important species on the planet.