In episode 81 of the Illinois Nutrient Loss Reduction Podcast, Dr. Lizzie French and Mick Goedeken from Waypoint Analytical discussed how soil microbes influence nutrient cycling, soil structure, and nutrient retention within agricultural systems.
The conversation focused on how the soil microbiome interacts with fertilizer management and conservation practices, and how understanding soil biology may help improve nutrient use efficiency while reducing nutrient losses from fields.
What is the soil microbiome?
French explained that the soil microbiome includes the microscopic organisms living in the soil, including bacteria, fungi, viruses, protists, and nematodes. These organisms play an important role in soil health and nutrient cycling, even though they cannot be seen.
According to French, microbes help:
- Break down crop residue
- Cycle nutrients into plant-available forms
- Build soil structure
- Support plant health
- Contribute to soil organic matter
She noted that a single spoonful of soil can contain billions of microorganisms working within the soil ecosystem.
Why soil biology matters
Goedeken noted that soil management has traditionally focused on chemical properties, such as nitrogen, phosphorus, and potassium, and more recently on physical properties like soil structure and compaction. Soil biology adds another piece to the picture of how soils function.
The discussion also highlighted nitrogen cycling within the soil system. French said microbes are responsible for processes such as nitrification and denitrification, which influence how nitrogen moves through the soil. Under wet conditions, nitrate-nitrogen can move out of fields and enter local waterways or be converted into gaseous forms by microbes, resulting in nitrogen loss. She noted that understanding these processes may help farmers evaluate nitrogen management decisions.
Measuring soil biology
French explained that soil biology tests can use microbial DNA to identify groups of microorganisms associated with specific soil functions, which may include:
- Nitrogen fixation
- Phosphorus solubilization
- Residue decomposition
- Mycorrhizal activity
This type of testing provides information about the functions microbes may be performing within the soil system.
Conservation practices and soil biology
French noted that many conservation practices already associated with soil health can also support soil microbial activity. Practices discussed included reduced tillage, cover crops, manure or compost applications, drainage management, and reducing soil compaction.
She said reducing tillage helps protect soil structure and fungal networks within the soil. Cover crops help keep living roots in the field longer throughout the year, while manure and compost provide carbon that feeds soil microbes.
French summarized the concept, stating that microbes need “food and housing.”
Nutrient retention and organic matter
Microbes contribute to nutrient retention in soils. French explained that microbes temporarily store nutrients such as nitrogen and phosphorus within their biomass. As microbes die and decompose, those nutrients are released back into the soil system.
Microbial activity also contributes to the formation of soil organic matter, which can help retain nutrients and improve soil structure over time.
The importance of pH and compaction
French noted that soil pH is one of the biggest drivers of soil biology. She said if soils become too acidic, biological activity may still be limited even when other soil health practices are being used.
Goedeken also discussed soil compaction, particularly across the Midwest. He noted that compaction can affect both crop roots and soil microbes, and that managing compaction is an important part of maintaining soil function.
The bottom line
Soil biology plays a vital role in soil health and nutrient cycling in agricultural systems, and agricultural conservation practices, such as reduced tillage, cover crops, manure or compost applications, and managing compaction, may help support soil microbial activity. Soil biology testing may provide another tool to help farmers better understand nutrient cycling and field variability within their operations.
To listen to the entire interview, go to episode 81 of the Illinois Nutrient Loss Reduction Podcast.
About the blog
At Illinois Extension, we’re working to improve water quality at home and downstream. Every month, our Watershed Outreach Associates bring you stories highlighting agricultural conservation practices, current research, and insights from the field. The Nutrient Loss Reduction blog covers conservation practices recommended by the Illinois Nutrient Loss Reduction Strategy, timely updates, and decision tools to help farmers reduce nutrients leaving their fields.
About the authors
Rachel Curry is an Agriculture and Agribusiness Educator specializing in agriculture and watershed education, and she is part of the Illinois Extension's Nutrient Loss Reduction Strategy implementation team. She holds a B.A. in Environmental Studies from Knox College and an M.S. in Environmental Science and Soil Science from Iowa State University, focusing on soil fertility. Her work centers on education and outreach related to the Illinois Nutrient Loss Reduction Strategy, promoting agricultural conservation practices that reduce nutrient loss while enhancing water quality and soil health across Illinois.
Nicole Haverback serves as a Watershed Outreach Associate and is an Illinois Extension team member implementing the Nutrient Loss Reduction Strategy. She holds a B.S. in Agricultural and Rural Policy Studies from Iowa State University. In her role, Nicole coordinates watershed management efforts aimed at reducing nutrient losses in two nitrate-nitrogen priority watersheds, offers expertise on best management practices to minimize nutrient loss, and leads outreach initiatives promoting agricultural conservation practices outlined in the Illinois Nutrient Loss Reduction Strategy.
Luke Zwilling serves as a Watershed Outreach Associate and is an Illinois Extension team member implementing the Nutrient Loss Reduction Strategy. He grew up on a farm in Jasper County and earned a B.S. in Agriculture and Biological Engineering from University of Illinois. Luke coordinates watershed-based activities to reduce nutrient loss in two phosphorus priority watersheds, provides expertise on best management practices for nutrient loss reduction, and conducts outreach on agricultural conservation practices in the Illinois Nutrient Loss Reduction Strategy.