Is conventionally
managed soil a
biological ghost
town?
Even soils receiving intensive tillage
and chemical inputs contain billions of
bacteria per gram of soil
Phil Brookes
Microherd
The soil beneath our feet may be teeming with a hundred
times more species of bacteria than previously thought,
according to biologists in New Mexico, US.
Measuring the bacterial biodiversity of soil is difficult
because only a few species can be cultured, according to
Jason Gans of the Los Alamos National Lab.
Fortunately, biologists can also estimate biodiversity
using a technique called DNA reassociation. This involves
chemically unzipping the two strands of all the bacterial
DNA in a sample, mixing them up and seeing how long
they take to join up again with matching partners.
SSSA
Their results reveal that there are a few
very common species in soil but lots of rare
species. "There is a very large number of
low abundance species," says Gans. So
many rare species, in fact, that the estimate
of bacterial biodiversity rises to ~ 1 million
species per gram of soil.
How much of the C in these corn stalks
will return to the atmosphere within 1
year?
> 75%
This is not possible without an active
microbial community
Corn
yie
ld
1950
30 b/a
150 b/a
A
B
C
Which trajectory for
SOM is most common
in the US?
How is it possible for
residue levels to
increase > 3x without
building SOM?
Broadbalk continuous wheat experimentData modelled by RothC-26.3 (solid lines)
0
20
40
60
80
100
1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020
Year
Organic C in soil
(t C ha-1) Farmyard manure annually
Unmanured
NPK
Why has the NPK program
resulted in so little increase in
SOM?
So
il C
(to
ns/h
a)
unfertilized
The manure and NPK systems are both producing > 100 bu/a wheat
The current OM level in a soil is a
result of the long-term balance
between organic inputs and outputs
The current OM level in a soil is a
result of the long-term balance
between organic inputs and outputs
Yield enhancing practices will not build
SOM if OM outputs increase at a
comparable rate to OM inputs
Organic outputs
”But with the removal of water through furrows, ditches, and
tiles, and the aeration of the soil by cultivation, what the
pioneers did in effect was to fan the former simmering fires…
into a blaze of bacterial oxidation and more complete
combustion. The combustion of the accumulated organic
matter began to take place at a rate far greater than its annual
accumulation. Along with the increased rate of destruction of
the supply accumulated from the past, the removal of crops
lessened the chance for annual additions. The age-old process
was reversed and the supply of organic matter in the soil began
to decrease instead of accumulating.”
William Albrecht – 1938 Yearbook of Agriculture
Drainage + Tillage + Lime + N + harvest = Accelerated loss of SOM
20 years of similar tillage and total organic
input but different types of organic inputs
manure
cover crops
crop residues crop residues
How do these soils differ ??
Rodale Institute Farming Systems Trial
http://www.grdc.com.au/growers/gc/gc48/conference1.htm
The development of
crumb structure is
a key step in
retaining SOM
Granular crumb structure Poor structure
We are well aware that a poorly
balanced diet for humans results in
heart disease, tooth decay,
obesity… what are the
consequences of feeding soil a
“white bread” diet?
White bread diet for soil = very little diversity of organic inputs
Acute
root
disease
Chronic root
malfunction
VS.
Unfortunately this is the
norm in agriculture
today :-<
Dramatic effect of steam
sterilization and compost on
growth of pepper plants
http://picturethis.pnl.gov/im2/8208417-5cn0/8208417-5cn.jpg
The digestive
capacity of soil
microorganisms
greatly exceeds
organic inputs to
soils.
accumulate at all
in soil?
So
why does
mat org anic ter
In the long run
…it remains largely unknown why some SOM persists for
millennia whereas other SOM decomposes readily…
Recent analytical and experimental advances have
demonstrated that molecular structure alone does not
control SOM stability: in fact, environmental and biological
controls predominate…
Nature, October 2011
The traditional concept of
large stable humus
molecules has been
rejected by most scientists
Mined humate products may
have value but are not the
same as old soil organic matter
Blackland soils of
North Carolina
Lily (1981)
> 1 million acres
Organic matter accumulates under anaerobic conditions
Impact of temperature on SOM accumulation
Brady and Weil (2002)
Temperature
Org
an
ic m
att
er
dyn
am
ics
Organic matter accumulates
in climates that support high
biomass production but limit
decomposition
Impact of temperature on plant growth
Brady and Weil (2002)
Temperature
Org
an
ic m
att
er
pro
du
cti
on
Impact of temperature on decomposition
Brady and Weil (2002)
Temperature
Org
an
ic m
att
er
co
ns
um
pti
on
Visualizing soil
habitat at biologically
relevant scales
Worm’s eye view?
Nematode’s eye view?
Visualizing soil habitat at
relevant scales
Bacteria occupy
< 5 % of soil surfaces
and < 0.1% of soil
porosity
Most of the pores where soil
microorganisms reside are either
environmentally suppressive or
lacking in suitable substrates.
Microorganisms have very limited ability to
move within the soil matrix.
As a result,
soil is a very sleepy place !
osmobiosis
anoxybiosis
thermobiosis
cryobiosis
anhydrobiosis
Most soil microorganisms are
in a dormant state
waiting…
For their prince charmings
to arrive !
Roots
Organic Amendments
Rain
There are many types of prince charmings !
Tillage
Dormant earthworm
SSSAJ 69(3) cover
Earthworm cocoons
offer much more protection
http://soils.usda.gov/sqi/soil_quality/soil_biology/images/CE8a-cocoon_LR_small.jpg
Most plants in your
soils are in a state
of dormancy
Seed dormancy
is much better
understood
than
microbial
dormancy
Who lives in the soil?
Bacteria
Fungi
Algae
Protozoa
Nematodes
Microarthropods
Enchytraeids
Earthworms
Ants, termites, spiders
Mollusks
Others: rodents, snakes,
voles, amphibians, etc.
Body size
increasing
Microflora
Mesofauna
Megafauna
Microfauna
Macrofauna
Soil organisms vary widely in size
Bacteria
Fungi
Algae
Protozoa
Nematodes
Microarthropods
Enchytraeids
Earthworms
Ants, termites, spiders
Mollusks
Others: rodents, snakes,
voles, amphibians, etc.
Microflora aka microbes
Mesofauna
Megafauna
Microfauna
Macrofauna
Most soil organisms are tiny !!!
Abundance
Soil
microbes
carry out
> 90% of all
decomposition
Soil animals have a
disproportionate impact on
nutrient cycling, energy fluxes
and plant growth
Soil animals are mobile
but have limited digestive ability
Soil microbes are relatively immobile
but have almost unlimited
digestive ability fungi bacteria
3 main types of digestive interactions
occur between soil animals and microbes
I want some
bacteria for
lunch ! Microfauna (e.g. protozoa and nematodes)
harness the microbes’s digestive abilities by
grazing on them
Microbivory
NH4+
NH4+
NH4+
NH4+
NH4+
NH4+
External
rumen
digestion
When mesofauna feed on fresh litter, their fecal
pellets contain shredded, moistened and mixed
but largely undigested residues
Reingestion of fecal pellets after a few days of
microbial activity greatly increases assimilation
Many
microarthropods use this digestive
strategy
Leaf cutter ants are a more
well known example of
external rumen digestion
Internal rumen digestion
greatly enhances utilization
of complex substrates by
soil macrofauna
Macrofauna are also
ecosystem engineers
Do roots and
macrofauna play
similar ecological
roles?
bacteria
root hair
rhizoplane
Microbial activation
Structural modification
Structural modification
Microbial activation
Navigating the rhizosphere
Rhizoplane
Endo-
Rhizosphere Ecto-Rhizosphere Root free soil
End of the rhizosphere
(Lavelle and Spain, 2001)
> 100 X
microbial
activity
Growing
Root
Aggregate
Disruption
Exudation
Release of protected
organic matter
Activation of
microorganisms
Priming
Effect
Why do roots have a priming effect?
(Lavelle and Spain, 2001)
Soil
organisms
are
concentrated
in
HOT
SPOTS !
Adapted from Coleman et al. (19??)
drilosphere porosphere
detritusphere aggregatusphere rhizosphere
middens casts
Drilosphere
Zone of
earthworm
influence
Detritusphere
surface residue zone
fungi
Clean tillage
eliminates the
detritusphere
Many soil organisms prefer to
feed at the surface
3 main
strategies for
managing soil
biology
Activation
Augmentation Conservation
Not all earthworms are sensitive to tillage…
but the ones that make vertical burrows
that connect the topsoil and subsoil are…
Earthworm functional
continuum
Epigeic Anecic Endogeic worms worms worms
Ectomycorrhizae
Arbutoid
mycorrhizae
Ericoid
endomycorrhizae
Orchid endomycorrhizae
AM endomycorrhizae
Mycorrhizal diversity
Lavelle and Spain (2001)
Most woody plants
Most herbaceous
plants including
corn and soybeans
Myco = fungus
Rhiza = root
•Many plants are
connected
underground by
mycorrhizal hyphal
interconnections.
•Mycorrhizal fungi
are not very host
specific.
Illustration by Mark Brundrett
Mycorrhizal Networks: Connecting
plants intra- and interspecifically
Mycorrhizal inoculants are available
but conservation of established networks is more important
Increase nutrient uptake
(especially P)
suppress pathogens
Mediate plant competition Improve soil structure
Glomalin
Superglue
of the soil ??
Mycorrhizae
Are you conserving the beneficial
fungi on your crop foliage?
Frogeye leafspot fungus resistance to strobilurin
chemistry a concern for Mid-South soybean growers Hembree Brandon - Mar. 2, 2011 5:36am
Add another to the growing list of weeds, insects, and diseases that have
developed resistance to the chemicals that farmers rely on to control pests and
protect yields — strobilurin-resistant Cercospora sojina, the fungus that causes
frogeye leafspot in soybeans.
The strobilurin chemistry has been widely used as a first line of defense in
preventing yield loss from Frogeye leafspot.
―There was documentation in 2010 of strobilurin-resistant Cercospora in Illinois,
Kentucky, and Tennessee,‖ Tom Allen said at the annual conference of the
Mississippi Agricultural Consultants Association.
Roots
Organic Amendments
Rain
Tillage
Biological activation strategies
Irrigation
Innovative cover cropping
is a great way to activate
your soil biology!!
Bio-strip till
attempt #1
September 2008
Radish planted on 30” rows using milo plates
in mid-August 2010
Attempt #3
Cover crop system Relative
corn yield
Volunteer oats 79%
Radishes planted on 30‖ 99%
Radishes drilled on 7.5‖ 91%
Corn following cover crop experiment in
2011 at the WIU Organic Research Farm
Corn planted on radish rows
Wheat + radish trial at the Allison farm
November 2010
3 lb/a = 2 lb/a = 1 lb/a > 0 lb/c
~ 2.5 bu/a yield boost
Is this an activation effect?
Have you tried any
biological seed
treatments?
Augmenting soil biology
Old school inoculation
http://www.beckerunderwood.com/en/pages/scienceofinoculation
VOTiVO contains a naturally occurring soil bacteria, or rhizobacteria, that live
and grow with the plant’s root system. The bacteria creating a biofilm that
becomes a living barrier limiting the number of receptor sites which could
otherwise be occupied by plant pathogens such as nematodes. Nematodes
use gaseous and solid exudates from the root as means to detect a root’s
proximity, so reduced levels of exudates can decrease the ability of the
nematodes to locate the receptor sites on the roots. The bacteria further
reduce viable nematode populations by consuming exudates, depriving
nematodes of an additional source of energy and nutrients.
competition parasitism
antibiosis induced resistance
Ask vendors to explain specifically
how their product works!
If you build it, they will come…
Do recognize this scene?
The most important biological management strategy
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