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YOUTH & FAMILIESAGRICULTURE HEALTH ECONOMY ENVIRONMENT ENERGY COMMUNITIES
Beyond the soil food web:
Managing soil for diverse
biological functions
Doug Collins
Small Farms Extension Specialist
WSU Extension
Outline and Learning Objectives
1. Understand functions
of soil organisms and
mutualistic
relationships
2. Tips to manage for
diverse and synergistic
functions
3. Monitoring soil quality
and function with soil
biological indicators
http://a.espncdn.com/photo/2012/0827/play_jetpack_d1_576.jpg
Important functions of a healthy soil
Magdoff & Van Es, 2009. Building soils for better crops
Supply nutrients from
organic sources.
Allow water & air to
infiltrate easily
Suppress root
diseases
Provide sufficient
water to plants
during dry spells
Develop healthy root
systems
Beneficial organisms
like mycorrhizal fungi
Classical soil food web models focus on predation and
competition.
These classical food web models ignore the
importance of larger soil fauna that encourage
decomposition and “spectacularly fail to
account for these sorts of relationships, or for
habitat modification by larger organisms for
smaller ones” – Wardle, 2002
Groups or guilds of soil organisms and their relative sizes
Body Width (mm)20 2 0.1 0.003 0.001 0.00001
millipedes
earthworms
springtailsprotozoa
nematodes fungi bacteria
primary consumers
secondary and
higher consumers
shredders/litter
transformers
ecosystem engineers
Litter transformers speed decomposition through an
“external rumen.”
Wolters and Ekshmitt, 1997
Earthworms are “ecosystem engineers”; changing their
environment to suit their physiology.
The earthworm’s kidneys; how earthworms answer nature’s call.
Earthworms deal with waste similarly to freshwater organisms
Earthworms increase aggregation in three ways:
1. By physically compacting smaller soil particles
together
2. By creating fecal pellets – which are themselves
durable aggregates
3. By coming to the soil surface to gather organic
matter to take down into their burrows.
Increased aggregation allows water to infiltrate easily during
a down pour and drain afterward to let air in.
Magdoff & Van Es, 2009
Infiltration Runoff
Quality soils supply nutrients from organic sources that
reduce the need for fertilizer
Nitrogen cycles from cover crops and amendments through
the microbial biomass
Isopods
Collembola
earthwormsnematodes
Microbial Biomass
Bacteria Fungi
available N Soil OM
protozoa
atmospheric N2
amendment
legume
C, N
N excreted
Management practices to encourage beneficial soil functions
• Use plant diversity to increase
the diversity in the soil biota
• Keep a living root growing
throughout the year
• Keep the soil covered as
much as possible
• Integrate livestock where
applicable.
• Manage more by disturbing
less
The Daily Worm:
“Mayan calendar predicts tornado, hurricane, and fire”
Larger-bodied organisms are more sensitive to disturbance
Body Width (mm)20 2 0.1 0.003 0.001 0.00001
millipedes
earthworms
springtailsprotozoa
nematodes fungi bacteria
high low
Sensitivity to disturbance
The roller / crimper, flail mower, and strip-tiller provide
opportunities to reduce soil disturbance
Reduced tillage research is underway for organic vegetables
Flail mowed and
strip tilledTilled
Kirsop farm, broccoli planted to flail mowed, strip-tilled common vetch.
8 July 2013, 21 DAT
Biotic indicators are ecological integrators, but not
necessarily easy to understand or inexpensive to measure
Idea soil health indicators should be:
1. Sensitive to variations in management
2. Well-correlated with beneficial soil
functions
3. Elucidate ecosystem processes
4. Understandable and useful to land
managers
5. Easy and inexpensive to measure.
Doran and Zeiss, 2000
Aporcelaimellus-
predator; 1.9 mm
Cephalobidae-
bacterivore;
0.5 mm
Aphlenchoides-
fungivore; 0.3mm
Rhabditidae;
bacterivore
0.1mm
Soil nematodes range in size, function, and sensitivity to
disturbance
stylet
Aphlenchoides;
stylet used to pierce
fungal hyphae
Aporcelaimellus; stylet
(spear) used to pierce
nematodes and protozoa
probolae
Cephalobidae; probolae used
to rasp bacteria from surfaces
Free-living soil nematode feeding strategies and structures
Isotomidae, juvenile
Isotomidae: Isotoma, adult
Entomobridae
OnychiuridaeSminthuridae
Hypogastruridae
Collembola are the most abundant soil microarthopods and
are fungal feeders, and litter transformers.
Earthworms can be coaxed from the soil with a skin irritant,
or physically removed.
Earthworm biomass by burrowing type in three tillage
systems 17 d after tillage, July 2011.
Anecic: p=0.3; Endogeic: p=0.001; n=3
Earthworm isolation from square in organic no-till plot.
Total earthworm biomass by tillage treatment and location
within planting bed, July 2011.
P=0.02 for location, P=0.18 for tillage, n=3
Research at WSU – Puyallup is investigating reduced tillage
frequency as well as amendment type.
Relay plantedLegume (RLY)
Fall-plantedCereal & legume (PH)
Short-term grass-legume Pasture (LEY)
Collembola populations spike in an annual pasture (LEY)
and with relay (RLY) planting that removes fall tillage.
• Dead ass collembola data
May Sep Jan May Sep Jan May Sep
Col
lem
bola
100
cc-1
0
20
60
80
100
120
LEY
PH
RLY
2005 2006 2007
** *** ** ** *
Compost applied in fields at 10 ton / acre or 2 ton/ acre.
Type of amendment did not significantly affect ratio of fungal
to bacterial-feeding nematodesNematode Channel Index
Type of Amendment
CKN OFC
0
1
2
3
4
5
Fungal-feeding nematodes spike in annual pasture (LEY). An
increase in the channel index indicates more fungal-feedersNematode Channel Index
Type of Cropping System
Ley PH Relay
Ch
an
ne
l In
de
x
0
1
2
3
4
5
a
b b
Feed the microfoodweb with plant diversity, but also manage
for mutualism.
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References
Doran, J.W. and M.R. Zeiss. 2000. Soil health and sustainability: managing the biotic
component of soil quality. Appl. Soil Ecol. 15:3-11.
Hunt, H.W. et al. 1987. The detrital food web in a shortgrass prairie. Biology and
Fertility of Soils. 3:17-68.
Kladivko, E. and J. Clapperton. 2011. Soil Biology. In: Hatfield, J.L. and T.J. Sauer
(editors). Soil Management: Building a Stable Base for Agriculture. American
Society of Agronomy and Soil Science Society of America, Madison, WI.
Magdoff, F. and H. Van Es. 2009. Building Soils for Better Crops, 3rd Ed. Sustainable
Agriculture Research and Education Program.
Turner, J. S. 2000. The Extended Organism. Harvard University Press, Cambridge, MA.
Wardle, D. 2002. Communities and Ecosystems: Linking the aboveground and
belowground components. Princeton University Press.
Wolters, V., K. Ekschmitt. 1997. Gastropods, Isopods, Diplopods, and Chilopods:
Neglected groups of the decomposer food web. In: G. Benckiser (editor). Fauna in
Soil Ecosystems: Recycling Processes, Nutrient Fluxes, and Agricultural
Production. Marcel Dekker, Inc, New York.
Photos: Clark County Historical Collection, Caitlin Price Youngquist, Andy Bary
Thank you!
Doug Collins
WSU Small Farms Program
253-445-4658
Examples of biologically-based soil health indicators
• Soil carbon / organic matter
• Soluble carbon / active carbon
• Microbial biomass
• Fungal to bacterial biomass ratio
• Microbial community diversity
• Enzyme activity
• Nematode indices
• Microarthopods
• Earthworms
Different soils will have different initial soil quality. Monitoring
through time is the best way to evaluate management
Soil A
Soil B
Time
Soil
Qual
ity