The Agronomists, Ep 97: Love your soil microbes with Drs. Kari Dunfield and Bobbi Helgason

Soil is alive and full of billions (yes billions) of fungi, bacteria, protozoa and more, performing key soil functions such as nutrient cycling, creating pores, and adding stability to soil structure.

But how much do we understand of our soils? And can we take steps to love these good bugs and get rid of the baddies? To explore what lies beneath, this episode of The Agronomists features Dr. Kari Dunfield, with the University of Guelph, and Dr. Bobbi Helgason, with the University of Saskatchewan.

Summary

• Can soil microbiologists pick their favourite microbes? Not a chance
• Why? Because soil microbes are so cool
• Water bears!
• Let’s scratch the surface (see what I did there) of the soil microbiome
• Billions of beasts below!
• Bacteria, fungi, nematodes, protozoa, all sorts of fun things
• Each has a role and function and some are detrimental to plants (pathogens) but many are not
• It’s a food web! Starts with the plant bringing energy down from the sun
• The microbes below interact with the plant, plant roots, soil particles, chemistry and each other
• It’s complicated, y’all
• Soil particles themselves play a role, and soil aggregates are created by microbes
• Sticky stuff from microbes is what creates pores and spaces
• What about chemistry? Salinity!
• Distribution sand, silt, clay. Clay is reactive, sand is less reactive
• Tillage and soil is complicated
• Tillage changes populations
• Some additions cause feeding frenzies!
• Then populations crash, and rebuild. It’s dynamic
• Great question: should we strive for more abundant soil microbes or different types?
• Both? Think of the soil microbe population as an engine, the total quantity determines the overall capacity, but the individuals are like cylinders, and all aren’t needed at all times
• It does matter that certain ones ARE there, though
• Soil your undies! Great way to measure soil microbe activity levels
• Types and number changes
• It’s more complicated, too, as the main driving factor for soil microbe levels was the presence of living roots/plants
• We know rotation makes better soil, but why?
• Balanced nutrition and different plant sources. Yes, there are differences in quality of carbon sources. Mind blown.
• The functionality of the microbes is super key
• Microbes don’t work alone
• You need different types to perform all the functions, no one microbe does it all
• Adding organic material matters. Manure is a great option
• Food is food, and manure contains lots of great carbon for microbes
• Does one plus one equal three?
• Soil microbiomes can be tricky and challenge the expectations/assumptions
• Old rules of thumb, for example, evolve as we have better diagnostic tools
• Fungal dominance in no-till is not necessarily true, for example
• The food source, having a plant there, makes a huge difference
• There may be more fungal substance in no-till soils, but it’s not all functioning/alive
• What about pH?
• The extremes of pH, very little can survive
• Wetter, lower pH can favour fungicides
• Temperature and moisture drive populations and cycles
• Exudates — do roots “recruit” microbes?
• Yes, but we don’t fully understand the process or the how/why
• Sugar will attract all sorts, but not specific microbes
• The very simple, all the way to two-way signalling systems
• It actually takes three to tango — plant, soil, microbes

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