A deeper look beneath the surface

By Dani Sheehan. 

Understanding the soil microbiome helps us move from just observing soil health to actually managing it. 

Soil is a living, breathing ecosystem with complex biological interactions that affect everything from crop health to long-term land productivity. In a recent Iowa Learning Farms webinar, Dr. Roland (Roli) Wilhelm, assistant professor of agronomy at Purdue University, broke down the current state of soil microbiome testing and what the future may hold for growers looking to manage their land more holistically. 

Dr. Wilhelm leads the Managed Ecosystem Microbial Ecology lab at Purdue and is at the forefront of research exploring how natural resource management affects soil organisms. He guided participants through the building blocks of the soil microbiome and explored how biological testing could become a more practical tool for farmers in the years ahead. 

Every field has its own biological fingerprint 

One of the most striking takeaways from Dr. Wilhelm’s presentation is how uniquely diverse and active soil life really is. Compared to environments like the ocean or human body, soil harbors the highest number of microbial species, many of which grow slowly and inhabit the countless neighborhoods created by soil’s spatial complexity. 

During the presentation, he explained that each of these organisms has its own function and role in making your soil either more resilient, more productive or both. For example, Myxococcus, a common soil decomposer with gliding motility and pack-like behavior, becomes especially active after plant harvesting. It’s one of many examples of how soil biology shifts in response to natural events and land management decisions. 

How soil microbes impact soil health 

Put generally, there are three functional groups of soil organisms that support soil health: 

1. Biochemical transformers: These are the workhorses of the soil, regulating 90% of the energy and carbon flow. Bacteria within this group are responsible for every step of the nitrogen cycle and help make critical nutrients like phosphorus available to plants. 
2. Biological regulators: These include predator-prey relationships in the microbial world that help balance populations. 
3. Ecosystem engineers: These microbes, including algae and cyanobacteria, influence physical properties of soil, like its structure and water retention, by promoting aggregate formation through the production of sticky extracellular substances (EPS). 

All of this microbial activity is essential for building healthy, resilient soils. So how do you encourage the right microbial activity in your soil? According to Dr. Wilhelm, it comes down to following well-established soil health principles, including: 

• Maximize continuous living roots 
• Maximize biodiversity 
• Minimize soil disturbance 
• Maximize soil cover 

These practices feed and protect soil microbes naturally. In addition, there are two more advanced biological strategies to consider: 

• Biostimulation: Adjusting soil conditions (e.g. moisture, organic inputs) to encourage the growth of beneficial native microbes. 
• Bioaugmentation: Introducing specific microbial species to support desired functions, such as nutrient cycling or disease suppression. 

Soil microbiome testing: Is it worth it? 

With new soil testing services popping up, many farmers are curious whether investing in microbiome data will translate into better management decisions. Dr. Wilhelm offered a grounded view, explaining that we’re not quite there yet, but we’re getting closer. The science is still evolving, and while patterns and predictions show promise, they’re best used alongside traditional soil health practices. 

For a deeper dive into soil health and microbiome testing, listen to the full webinar from Iowa Learning Farms.