Interactions in Soil
and Compost
By Pat Patterson
OSU Extension MG & CS
Soils and Compost share many of
the same bio-life and chemical
processes. Still there are some big
differences in how these play out.
Most soils break down organic
matter and minerals using organisms
which are at home in its cooler
environment as compared to a hot
compost pile.
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Importance of Compost Maturation
As compost cools and matures, its
living content also starts to change,
often becoming more like that in soil.
Major difference is that the compost
has a higher concentration of the
enzymes, humus, organic matter
than the soil. It thus has a very high
potential for holding nutrients, water
and ion exchange ability.
What Is in a Soil?
Clay, silt & sand
Various minerals
Water
Air
Organic matter
Humus
Living organisms:
roots, animals,
microorganisms
Humus is the most
friendly texture for
bacteria. Its great
surface area and
high reactivity
afford them many
opportunities. The
limiting factor is C &
N and gases usually.
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There are 3 main components of organic
matter in soils:
dead forms of organic material - mostly
dead plant parts
living parts of plants - mostly roots
living microbes and soil animals
By far the largest component is the
dead matter - it constitutes about 85%
of all organic matter in soils. Living
roots make up about another 10% and
the microbes and soil animals make up
the last 5% percent.
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What Is in Compost
A high number of diverse organisms.
Large amounts of organic matter:
semi-decomposed and fairly stable
(humus)
Organisms vary from microscopic to
clearly visible.
Gases, water and mineral elements
Soil Organisms Trump Compost
Organisms
In a bio-active, balanced soil, resident
organisms will usually out compete and
displace introduced organisms not native
to that soil.
In a deficient soil, compost organisms will
jump start the necessary process to create
the proper soil community.
Plants present will select for their desired
soil life partners.
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Ways to Change Soil Interactions
If a soil is anaerobic and you add
good compost, the aerobic organisms
will claim the soil.
If a soil has good tilth and biolife
already, changing the plant
community will change the
organisms present, perhaps opening
niches for the compost organisms.
Compost loses biological diversity
the longer it sits
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Categories
Oxygen Needs
Aerobic
Anaerobic
Facultative
Temperature Needs
Psychrophilic
Mesophilic
Thermophilic
Let’s consider the microlife
and processes in compost and
in soil.
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How does compost happen?
The food web in
the compost pile
is made up of
many different
organisms.
Each plays a role in
the breakdown of
organic matter.
It is a reductive
process for OM
Nature Is the Ultimate Composter
All organic matter is destined to
become humus in the natural
system.
Trees and bones take a bit longer, as
do most of the processes for surface
deposited organic matter.
Higher N sources and temperatures
and moisture accelerate the process.
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Tropical rainforest soils tend to not
build humus. Why?
Desert soils tend to not build humus.
Why?
Microorganisms in Soil
Archaea, Bacteria, fungi, actinomycetes,
protozoa, nematodes, mites, waterbears,
algae , insects
Present in large numbers, but often in zones
Feed directly on organic matter or each other
or operate in symbiosis with plants
Most not tolerant of high composting temps
No need for “compost starters”, though
biodynamic preps do make a difference
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Macroorganisms in Compost
These move in only after the
temperatures are past the high heat
phase.
Many arthropods (bumblebees to
worms)
Slugs and snails
Snakes
Mammals: mice and voles
Let’s do a general overview of
the various living elements
drawn in by organic matter.
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Archaea
Previously classed with Bacteria, they
are now placed in another kingdom, with
DNA related to bacteria and to all the
other life forms.
These are noted for adaptation to
extremes: hot pools, depths of the soil,
extreme cold.
With better detection methods, these
are now found in regular soil and in
compost.
Archaea
Archaea and bacteria are now being
identified by DNA patterns. Visually
they are almost impossible to
differentiate.
They are often abundant around the
roots of garden plants.
Many can fix atmospheric nitrogen
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Archaea
Many types. Here are just two.
Halogenic
archaea
Methanogenic archaea
form a symbiosis
with termites.
Archaea & Bacteria
Some can transform inorganic forms,
change organic to inorganic minerals.
They cause most of the renewal of
our earth by recycling & making
available all the essential elements.
The metabolic activity of the
microbes in the top 6” of an acre of
rich soil is greater than that of
50,000 human beings.
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Bacteria
“Workhorses” of the
compost pile and the
soil.
Smallest (single-celled)
and most numerous
Different species at
different temperatures
Bacteria: the Horde
Bacteria do the lion’s share of work
in the soil. They will be present at
1012 close to the roots of plants.
Bacteria are the heaviest users of N
at 5:1
A well-balanced soil will have a
preponderance of “good” bacteria, a
killed soil will be recolonized by
“bad” ones.
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Bacteria
Most pathogenic bacteria prefer a low
oxygen environment.
Most bacteria are in some way
beneficial.
“Good” bacteria turn away bad ones by
competition, by eating them, by using
antibiotics as weapons in an aerated
environment.
We get pesticides (Bt/Serenade) and
medicines from them.
Bacteria
Bacteria take in nutrients in several
ways. The most interesting is when
membrane proteins use energy to
suck or push nutrients through the
cell wall. Like a bucket brigade.
(Teaming with Microbes, Revised
Ed.)
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Bacteria
Bacterial slime consists of sugars,
proteins & DNA.
Bacteria can go into a resting stage
for centuries (or more)
Bacteria tend to push pH towards 7.0
They have existed on earth for at
least 3 billion years.
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Rhizobacteria
http://interactive.usask.ca
Actinomycetes
Look like fungi, but are filamentous
bacteria
Give compost and good soil an “earthy”
smell
Break down tough, woody debris fungi
cannot
Some look like gray spider webs
stretching through compost
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Actinomycetes
They can take N gas from the air and
convert it to ammonia in the soil. They
associate with many plants, not legumes,
unlike the rhizobial bacteria.
Yearly, microbes fix about twice as
much as the total nitrogen produced
industrially.
Actinomycetes
www.ehponline.org
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Comparative measurement
If you were the size of the state of
California you would be 600 miles
long
A gram of soil would be 4 miles long,
wide and tall
Protozoa as long as a football field
A bacterium as long as a school bus
A virus the size of a worm
The first soil antibiotic used in
human medicine was isolated
from an actinomycete and was
called actinomyacin. It was
effective where penicillin
failed. It was discovered by a
soil microbiologist who was
scoffed at by other scientists
as “nothing major comes of
studying soil biology.”
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Fungi
Break down tough debris and residues that
are too dry, acidic or low in N for bacteria
Thrive where oxygen is plentiful
Present in cold and hot composting piles
Present in most soils, though most in forest
soils
Fungi-the conveyer belt
Fungi have networks of mycelial strands
in a healthy soil.
Fungi enter into reciprocal agreements
with the plants, as do the bacteria.
Fungi extend the usable nutrient and
water area for a plant’s roots.
Fungi help plants share nutrients, even
across species.
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Mycorrhizal
Fungi
Ectomycorrhizae
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Ecto- & Endomycorrhizae
Soil Fungi
Create a plant guild by linking even
dissimilar plants which share nutrients
and signaling.
Extend the useful root area for
symbiotic plants
Some form an intimate union with some
plants.
May be predatory
May be pathogenic
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Fungi
Fungi can transport nutrients in
cytoplasm from any point in the hyphal
net.
Fungi can immobilize nutrients so they
cannot leach.
They can grow up to 40 micrometers a
minute.
Dead fungal tubes are safety zones for
bacteria avoiding hungry protozoa.
Fungi
Fungi produce acids to help break down
foods. Thus, they tend to counteract
the alkalinity of the bacteria so the soil
or compost tends more to 6.5 pH, ideal
for most plants.
They are especially efficient at mining P
into a usable form.
Plants have “trained” fungi to be a
nutrient pipeline.
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Fungi
At least 90% of all plants form
mycorrhizal partners and the
partnership started about 450 million
years ago. It is probably how plants
were first able to establish themselves
in soil.
Compaction, most chemicals, rototilling
all destroy fungal hyphae. Even air
pollution can damage some fungi.
“There are some things even a
fungus will not swallow”
– J C Jenkins
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Algae
Algae in a compost pile are probably
not a good sign.
In the soil they add a sticky organic
matter which helps the structure.
Those things called algae may be
plantlike, bacteria or even protozoa.
They have been found in most soils,
even deserts
Protozoa
One-celled microscopic animals
Found in water in compost
Very common in most soils
Ingest organic matter, bacteria, fungi
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Protozoa
These are major nutrient recyclers,
depositing them in the soil in a plant
ready form.
They survive only in a soil with enough
cohesive water.
Tend to be different proportions of
each in compost and soil.
Ciliates common in soil, not as desirable
in compost, especially for tea.
Protozoa
Over 60,000 kinds
Three basic forms:
– amoebae which form false feet (think,
The Blob)
– Ciliates with rows of “oar hairs.” The
school lab paramecium is one of these.
Many can live in anaerobic conditions.
– Flagellates with one or two long whiplike organs foe propulsion.
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Population Control
On average, a protozoan will eat 10,000
bacteria a day.
This keeps the bacteria from
overpopulating a system
It also releases the excess nutrients
from the bacteria not needed by the
protozoan. Up to 80% of the N needed
by the plants.
Protozoa often also outcompete
nematodes.
Naked amoeba soil protozoa eat thousands
of bacteria daily.
Wilhelm Foissner, Institute of Zoology,
University of Salzburg
http://www.blm.gov/nstc/soil/protozoa/index.
html
Testate amoeba soil protozoa make
a protective shell of silica, soil
particles or calcium.
Photo credit:
Wilhelm Foissner, Institute of
Zoology, University of Salzburg
http://www.blm.gov/nstc/soil/protozo
a/index.html
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Ciliate
usda.gov
Flagellates
www.stanford.edu
www.blm.gov/
www.microscopy-uk.org.uk
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Protozoa Meets Fungi
Paramecium
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Macroorganisms in Soil
Arthropods with ants at the top of
their food chain
Slugs and snails
Many worms and nematodes
Mammals
Reptiles
Microbe populations in compost
and Soil
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Nematodes
Microscopic, cylindrical, often
transparent roundworms
Most abundant of physical
decomposing animals
They often serve as a “taxi”
for bacteria & fungi.
Nematodes
Some scavenge on decaying vegetation
Some are plant root feeders
Some are predatory. These feed on
bacteria, fungi
They are snacks for fungi & some
protozoans
Their waste product makes the
nutrients plant available also.
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•Also known as roundworms
Nematodes
•Microscopic to 30’ in length
•Need porous soil
Elaine R Ingham http://soils.usda.gov
Electron microscope
view showing nematode
parasitic bacteria
attached to plant
parasitic nematode
Photo credit: SSSA
Electron microscope view of
nematode head
Photo credit: Sven Bostrom,
Swedish Museum of Natural
History
Head of Cervidellus
spitzbergensis
Photo credit: Sven
Bostrom, Swedish Museum
of Natural HIstory
http://www.blm.gov/nstc/soil/nematodes/index.html
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Fungi devouring Nematode
Arthropods Micro and Macro
Johnny N. Dell, Retired, www.forestryimages.org
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Decomposer Mite
Soil Mites
Some scavenge on
organic matter and
serve as “shredders”
Some eat fungi
Some are predators on
other critters
Only in cooled compost
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Microscopic soil mite
Springtails
Small, wingless, jumping insects
Many, many kinds with different habits
Eat decomposing plants, fungi, and
nematodes
Subsoil forms don’t jump and are usually
blind
Foresters say springtails drive the forest
system.
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Springtails
Springtails
Above ground springtails can leap
randomly.
Snow and sand “fleas” are springtails.
Springtails love bacteria, fungi and
decaying organic matter.
Mites love to eat springtails, as do
pseudoscorpions.
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A Few Other Detritivores
millipedes
Sowbugs & pillbugs
slugs
•Fruit Flies
•Fungus Gnats
•Black Soldier Flies
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Soldier Flies
Soldier flies have a special place in
composting.
They can actually be a main force in
reducing organic matter.
We used to think they were a problem
because the compost was too wet, but
now they are being studied as a major
compost method, like worms.
Soldier Fly Larvae
insects.tamu.edu
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Predators of the compost pile &
soil
Rove beetle
Such predators will be found in
the cooled compost pile only
Centipede
Centipede
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Harvester ants
Pseudoscorpions
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Earwig
Psocid
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Millipede
Earthworms
Important in soil and composting.
Vermicomposting is another branch of the
composting science.
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Fungal or Bacterial?
All living soils contain high
populations of fungi and bacteria.
Whether the soil is primarily run by
fungi or bacteria depends on the
plant life present.
A forest is fungally dominated.
A field or garden is bacterially
dominated.
What Kind of Compost?
Composts heavy in woody wastes tend to
favor fungal dominance.
Composts heavy in vegetable wastes
tend to favor bacterial dominance
You can build a designer compost for
your plants and soil
A compost balanced with woody and
green wastes is most versatile, easily
able to adapt to the new soil and plants.
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Fungal or Bacterial
All live soils contain about the same
range of bacteria, but the fungal
component varies greatly.
The chart gives a rough idea of how this
works.
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Plant Partners?
Up to 60% of the plant’s sugars go to
the roots and 1/2 of that is put into the
soil medium to attract and feed
bacteria and fungi.
The drawing in of the micro-organisms
then builds the soil structure, releases
nutrients and minimizes diseases. Soil
toxins are also then broken down.
The Web of Life
The live part of soil is temperature driven.
It functions best at 50oF or above. If the
diverse population of microbes in the soil
were to fail in their functions, life for
higher plants and animals would cease.
Most beneficial organisms prefer aerated
soil
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The Web of Life
Sweet, hot compost requires primarily
aerobic microbes.
Cold composting can be aerobic or
anaerobic. There is a place for both
kinds.
Bokashi is a fermentation, anaerobic
process
Bibliography
The Soil and Health by Sir Albert Howard
An Agricultural Testament by Sir Albert
Howard
Edaphos: Dynamics of a Natural Soil
System by Paul D. Sachs
Teaming with Microbes: A Gardener’s
Guide to the Soil Food Web by Jeff
Lowenfels and Wayne Lewis
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Bibliography cont.
Soil Biology Primer USDA NRCS
Soil Fertility by Jerome D. Belanger
Fertility without Fertilizers by Lawrence D.
Hills
Life in the Soil James B. Nardi
Let It Rot by Stu Campbell
Life in the Underground by David Wolfe
Your Compost Manual!
Be sure to watch the video “Worm Bin
Creatures Alive through a Microscope”
Great Websites
soilfoodweb.com Dr. Elaine Ingham
http://compost.css.cornell.edu/Composting
homepage.html
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