Download Earthworms and Soil Health

EARTHWORMS AND SOIL HEALTH
Jodi Johnson-Maynard
1/21/14
UNIVERSITY OF IDAHO
SOIL HEALTH
• “The capacity of a specific kind of soil to function,
within natural or managed ecosystem boundaries,
to sustain plant and animal productivity, maintain or
enhance water and air quality, and support human
health and habitation”
–USDA
• Key elements
•
•
•
•
Sustain productivity- long term
Relationship to water and air quality
Human health
Soil biology
SOIL HEALTH
“We should allow the soil to work for us
and not work against it”.
(Elliott and Coleman,1988)
Recommendations
1) reduce tillage
more and better quality SOM
increase microbial biomass
increase macroporosity
2) minimize use of biocidal compounds
CHALLENGES
•
•
•
•
Long-term, may not see immediate benefit
Dynamic
Site-specific
Quantification
SOIL HEALTH
Example Indicators
Soil structure
Infiltration rate
Bulk density
Water retention
pH
Extractable N-P-K
Microbial biomass C and N
Soil respiration
Soil organic matter
20 – 30 x’s biomass d-1
Ingest 100 to 1000 Mg of
dry soil ha-1 yr-1
Surface casting species
move 40 t ha-1 yr-1
(Feller et al . 2003)
Annual flux of N through
biomass =10 to 74 kg ha–1
year–1
(Whalen & Parmelee, 2000)
Earthworm Jim
Across the globe:
length - 2 m to a few mm
weight - 10 mg to a kg
diameter - up to 40 mm
Across the IPNW:
Driloleirus sp.
Photo:
Brita
Olson
Photo:
Andre
a Zcisi
A. trapezoides
EARTHWORM ECOLOGICAL GROUPS
• Epigeic species
feed on undecomposed litter and live within the first
few cm of soil; <10 cm in length
 Anecic species
feed on surface litter and live in permanent burrow
systems that may extend several meters; > 15 cm in
length
 Endogeic species
feed on soil and associated organic matter and live in
horizontal, non-permanent, branching burrow systems;
10-20 cm in length
(Bouche, 1977)
Casts
Burrows
BURROWS
Increase infiltration,
reducing runoff
Increase movement of air
and water
within profile
Habitat for other organisms
anecic
endogeic
(Figure
from
Blouin et
al., 2013)
DRILOSPHERE
 Enriched C and N
 Increased microbial
activity
Residue,
mucus and
casts
 Increased populations of
grazers(protozoa,
nematodes, and
collembola)
 Increased C and
N mineralization
CASTS




Enhance aggregate stability
Stabilize C
Mesopores and micropores
N mineralization
EXAMPLE: EARTHWORM ACTIVITY
AND SOM
Increase microbial
activity and
decomposition
Increase respired CO2
Loss of soil organic
matter
Increase nutrient
availability
Increase plant
biomass
Cast production
Increase physically
protected C
Gain of soil organic
matter
PREDICTING EARTHWORM IMPACTS
What do we need
to know?
 Species present
• Ecological habit
• Typical density
and biomass
values
• Activity periods
MEAN ANNUAL PRECIPITATION
SPECIES
• Aporrectodea
trapezoides
• Aporrectodea
tuberculata
90% of adults over a 2-year survey
Endogeic or epi-endogeic
• Aporrectodea
calignosa
DENSITY
REGIONAL DISTRIBUTION
ACTIVITY
FUTURE WORK
• Controlled mesocosm experiment to quantify the
impact of temperature and moisture on earthworm
survival, reproduction and aestivation rates
• Use of 15N labeled wheat residue to determine the
impact of earthworm activity on N uptake by wheat
• Continued field sampling to determine, more
specifically, seasonal changes in activity
SUMMARY
• Earthworms can have strong positive impacts on
chemical and physical indicators of soil health
• These impacts depend on earthworm density, species
and feeding/burrowing behavior
• Must consider density and activity period in climates
with significant dry periods
• The most common species in IPNW agroecosystems
may have greater influence over chemical/fertility
indicators than physical
• Specific soil quality indicators may change at different
rates and be more or less sensitive to management