Transcript Soil Microorganisms And Their Functions

Happy Critters
Healthy Soils
Mark Scarpitti, CCA
State Agronomist, Ohio NRCS
(740) 653-1500 ext 103
[email protected]
Bacteria
Are single cell organisms
(and are therefore microscopic)
• There are 100 MILLION to 1 BILLION bacteria
in just 1 TEASPOON of soil!!!
What Bacteria Do
• They are decomposers, eating dead plant
material and organisms' waste
• The bacteria release nutrients
Do you know what soil smells like?
Actinomycetes, a unique type of
bacteria, cause that smell, and it is a
good sign of healthy soil.
Actually, people have been smelling soil
for many, many years as a way to judge
if the land is good for planting.
A Few Important Bacteria
Nitrogen-fixing bacteria form symbiotic
associations with the roots of legumes
•The plant supplies to the bacteria
and the bacteria convert nitrogen (N2)
from air into a form the plant can use.
•When leaves or roots from the host
plant decompose, nitrogen is released in
the surrounding soil.
Nodules formed where
Rhizobium bacteria infected
soybean roots
A Few Important Bacteria
Denitrifying bacteria convert nitrate to nitrogen (N2) or
nitrous oxide (N2O) gas
Denitrifiers are anaerobic,
meaning they are active where
oxygen is absent, such as in
saturated soils or inside soil
aggregates
Nitrogen loss can result in
yellow looking corn plants
A Few Important Bacteria
Nitrifying bacteria change ammonium
(NH4+) to nitrite (NO2-) then to nitrate
(NO3-) – a preferred form of nitrogen for
grasses and most row crops.
Nitrate is leached more easily from the soil,
so some farmers use nitrification inhibitors
to reduce the activity of one type of
nitrifying bacteria.
FUNGI
Fungi are organisms
•They are not plants, nor are they animals
•They group themselves into strings called hyphae
The hyphae then form
groups called mycelium.
They are less than an
1/32 of an inch wide but
can get as long as
several meters.
The Good and Bad and the Fungi
They are helpful but can also be harmful
Fungi are helpful
•because they have the ability to break
down nutrients that other organisms
cannot
•Fungi release them into the soil, and
other organisms get to use them
•Fungi can attach themselves to plant
roots. Most plants grow much better
when this happens.
•This is a good relationship called
mycorriza
The Good and Bad and the Fungi
They are helpful but can also be harmful
Some Fungi can be harmful
• Fungi can get food by being
parasites, attaching
themselves to plants or
other organisms, but offering
nothing in return
A Few Important Fungi
Decomposers – saprophytic fungi – convert dead organic material
into fungal biomass, carbon dioxide (CO2), and small molecules,
such as organic acids.
Like bacteria, fungi are
important for immobilizing, or
retaining, nutrients in the soil.
A Few Important Fungi
Many byproducts of fungi are organic acids:
• Humic-acid rich organic matter is resistant to degradation for
hundreds of years
Like bacteria, fungi are
important for immobilizing, or
retaining, nutrients in the soil.
A Few Important Fungi
Mutualists – the mycorrhizal fungi – colonize plant roots. In
exchange for carbon from the plant, mycorrhizal fungi bring soil
nutrients (phosphorus, nitrogen, micronutrients, and water) to
the plant
One major group of mycorrhizae,
the ectomycorrhizae grow on the
surface layers of the roots
MYCORRHIZAL FUNGI
IN AGRICULTURE
Mycorrhiza: a symbiotic association between
fungi and plant roots
•Fungi can serve as a bridge to bring
nutrients to plant roots
•Under dry conditions, fungi can bring
moisture to the roots they colonize
MYCORRHIZAL FUNGI
IN AGRICULTURE
Practices that affect the formation of mycorrhizae:
• Mycorrhizal fungi will decline in
fallowed fields
• Mycorrhizal fungi will increase in fields
planted to diverse crops or cover crops
• Tillage drastically reduces fungi
• Broad spectrum fungicides are toxic to
mycorrhizal fungi
• High levels of fertilizer reduces
inoculation of roots
PROTOZOA
Protozoa are organisms that have only one cell, and
are microscopic, but larger than bacteria
They are grouped by
the ways they move:
• Amoebae use a psuedo (fake) foot
• Ciliates have cilia (short hair) and move very fast
• Flagellates have flagella (whips) and move very fast
PROTOZOA
Protozoa need:
•Bacteria to eat
•And water in which to move
So moisture determines which types of
protozoa will be present and active.
Like bacteria, protozoa are
particularly active in the rhizosphere
next to roots
Cool Things About
PROTOZOA
Protozoa eat bacteria
• Bacteria have a C:N ratio of about 3:1
• Protozoa have a C:N ratio of about 10:1
This means that protozoa do
not need all the nitrogen they
consume and so excrete
nitrogen in a plant available
form
Bacteria Ingested by an Ameba
WHAT DO PROTOZOA DO?
Protozoa
• Mineralize nutrients
• Regulate bacteria populations
• Serve as a food source for other organisms
• Help suppress disease by
feeding on pathogens
NEMATODES
Worms typically 1/500 of an inch (50 µm) in
diameter and 1/20 of an inch (1 mm) in length
Most nematodes in the
soil are not plant
parasites. Beneficial
nematodes help
control disease and
cycle nutrients.
Credit: Elaine R.
Ingham, Oregon State
University, Corvallis
NEMATODES
There are a few species responsible for plant
diseases, but not much is known about the
majority of nematodes that are beneficial
This bacterial-feeding
nematode, Elaphonema,
has ornate lip structures
that distinguish it from
other nematodes.
Bacterial-feeders release
plant-available nitrogen
when they consume
bacteria.
Credit: Elaine R. Ingham,
Oregon State University,
Corvallis
WHAT DO NEMATODES DO?
Nutrient cycling:
Like protozoa, nematodes
are important in
mineralizing, or releasing,
nutrients in plantavailable forms
Root Feeding Nematode:
A predatory nematode
consumes a smaller
nematode.
Credit: Kathy Merrifield,
Oregon State University,
Corvallis.
WHAT DO NEMATODES DO?
Disease suppression:
• Some nematodes cause disease
• Others consume disease-causing organisms, such
as root-feeding nematodes, or prevent their access
to roots
• These may be potential biocontrol agents
WHAT DO NEMATODES DO?
Disperse microbes:
Nematodes help distribute bacteria and fungi
through the soil by carrying live and dormant
microbes on their surfaces and in their digestive
systems.
ARTHROPODS
Arthropods are invertebrates - they have no
backbone Rather they have a covering called an
exoskeleton.
Sowbugs are relatives of crabs
and lobsters. Their powerful
mouth-parts are used to
fragment plant residue and
leaf litter.
Credit: Gerhard Eisenbeis and
Wilfried Wichard. 1987. Atlas on
the Biology of Soil Arthropods.
Springer-Verlag, New York. P. 111.
WHAT DO ARTHROPODS DO?
Although the plant feeders can become pests, most
arthropods perform beneficial functions in the soilplant system
WHAT DO ARTHROPODS DO?
•Shred organic material
•Stimulate microbial activity
•Mineralize plant nutrients
ARTHROPODS
IN AGRICULTURE
Control pests:
Some arthropods can be damaging to crop yields, but
many others eat various root- and foliage-feeders
Tillage and insecticide application have
enormous effects on non- target species
in the food web
Intense land use (especially
monoculture, tillage, and pesticides)
depletes soil diversity
As total soil diversity declines, predator
populations drop sharply and harmful
populations can reproduce exponentially
EARTHWORMS
Of all the members of the soil food web,
earthworms need the least introduction
Their presence is
usually an indicator
of a healthy system
EARTHWORMS
IN AGRICULTURE
Earthworms mix the soil
As they consume organic
matter and mineral
particles, earthworms
excrete casts, a type of soil
aggregate.
Earthworm cocoons
One or two worms will hatch
from a cocoon after several
weeks. L. terrestris cocoons are
about a quarter inch long.
Credit: Clive A. Edwards, The Ohio
State University, Columbus
Decomposers
Earthworm pulled
plant residue into
burrow
EARTHWORMS
IN AGRICULTURE
Increase infiltration.
Earthworms
enhance porosity as
they move through
the soil. Some
species make
permanent burrows
deep into the soil.
Bury and shred
plant residue
Earthworms eat
residue, digest
and excrete rich
organic matter
Conclusions
•A healthy soil will contain an abundant, diverse
population of soil organisms
•A diverse healthy population of soil organisms can
self regulate and is sustainable
Conclusions
The best tools we have to nurture an abundant,
diverse population of soil organisms
• No Tillage Cropping Systems
(when you till, you kill)
• A diverse Conservation Crop Rotation and/or use
of diverse Cover Crop mixes
• Maintaining a living root year round through the
use of a diverse Conservation Crop Rotation
and/or use of diverse Cover Crop mixes