Soil Microbial Life:
An introduction
Grant McCarty
Local Foods and Small Farms
Systems Educator
Jo Daviess, Stephenson, and
Winnebago Counties
(Northern Illinois)
Source: University of Illinois
Extension
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Today’s Plan
• Soil Biology
• Soil Organic Matter
• C:N Ratio
• Positive and Negative
Influences
• The players and their
roles
Source: University of Illinois
Extension
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Source: flickr
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Soil Biology
Source: cals.ncsu.edu
Source: NRCS, University of Illinois
Extension
• Are a part of Soil
Organic Matter (SOM)
• Job: recycling,
breaking down, and
competing for
resources
• Assists release of
important plant
nutrients
• Decomposers and
Predators
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Soil Biology
• Most biological activity
occurs around
rootzone (rhizosphere)
• Release of exhudates
and others
Source: NRCS, University of Illinois
Extension
• Warm temperatures,
warm soil = population
increases
• Natural influences
effect populations
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Soil Biology
• Positive Influences
• Addition of organic
matter
• Reduced tillage
• Cover crops
• Crop rotation
• Mulching
• Negative Influences
Source: nesare.org
• Drought/floods
• Fallow periods
• Heavy tillage
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Organic Matter
• Manures, composts,
plant residues
• Bacteria tend to use simpler
organic compounds like root
exudates or fresh plant
material
• Fungi like fibrous plant
residue, wood, and soil
humus.
Source: university of Illinois extension
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Organic Matter
• Carbon:Nitrogen Ratio is
very important
Source: msu.anr.msu.edu
• A low nitrogen content or a
high c:n ratio is associated
with slow soil organic matter
decay
• Less than 24:1- 4 to 8 weeks
to decompose
• Greater than 24:1- need
nitrogen and slows down
decomposition
• Ex. Rye Straw- 82:1
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The Decomposers: Fungi
Source: University of Illinois
• Produce hyphae that move
through soil particles
• Assist with water, nutrient
cycling, disease suppression
• 3 groups: mutualistic,
pathogens, decomposers
• Location: most near woody
plant residue
• Can tolerate dry conditions
but need air
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The Decomposers: Fungi
• Mycorrhizal
• Symbiotic relationship
between fungi and plant
roots
• Can assist in nutrient and
water uptake of the plant
• Varies from plant to plant
• Ex. Black truffle
Source: The Ohio State University
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The Decomposers: Bacteria
Source: University of Illinois Extension
• Teaspoon of soil: 100 mil
to 1 bil
• 4 different types
• Convert E in SOM for
other organisms
• Assist nutrient cycling,
disease suppression
• Can fix N on leguminous
plants
• Leaves/roots degrade for
additional
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The Decomposers: Bacteria
• Change NH4+ to N02and NO3• Location: fresh, young
plant residues and
compounds near roots
• Around rhizosphere
Source: University of Illinois Extension
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The Predators: Protozoa
Source: University of Illinois Extension
• Feed on bacteria
• Three different groups
with movement
dependent on water
• Important role in
nutrient cycling
• Protozoa eat bacteria
which release excess
ammonium
• Taken up by organisms and
plants
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The Predators: Nematodes
Source: eXtension.org
• Microscopic worms
• Eat bacteria, fungi,
protozoa/nematodes
• Assist with nutrient
cycling
• Grazing to stimulate
populations
• Disperse microbes
around soil
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The Predator: Earthworms
• Tends to be a shredder
• Major decomposer of
dead and decomposing
organic matter
• Eat bacteria/fungi on
these
Source: flickr
• Stimulate microbial
activity, positive influence
on SOM, increase
infiltration
• Location varies by species
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The Decomposers: Earthworms
• Typically, Increase with
SOM
• Ag Soils: Lumbricidae
• More common in north and
east
• More abundant in loam and
clay
• Build up in irrigated soil
Source: flickr
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Source: flickr
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What to do next
• Keep them happy
• Add to your soil
• Keep the soil covered
• Crop Rotate
• Diversification
Source: flickr
• In your rotations, covers,
organic matters
• Add both fresh material
and aged
• More to come later…
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Questions?
[email protected] / 815-986-4357
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