Measuring soil biology
In one single teaspoon of soil there can be
more soil organisms than there are humans
on earth!
Difficult to test for soil biology is a very complex system
Numbers and types change rapidly with
Temperature – day/night, depth of soil
Moisture – rain, irrigation, drought
Nutrient supply – organic matter type, &
amounts – crop or pasture
Take outside factors into account in tests!
How DO we test for soil
organisms?
Can use
• Direct indicators for presence, activities
and/or numbers
– Single or range of species in field e.g. ants
– Biological lab tests – enzymes, DNA e.g. microflora and –fauna
– Chemical lab tests – microbial biomass, CO2
respiration
• Indirect indicators which affect function of
organisms
– Organic carbon
Tests available
Numbers/Mass (how many
are there?), Diversity (who
are they?) and Functions
(what do they do?)
• AMOUNT: reasonably stable but assessed withOUT
separating into groups
– E.g. bacteria and fungi (microscopy, plate counts- only retrieve 12% actual amount), microbial biomass carbon or nitrogen (most
commonly used).
• ACTIVITY – fluctuates with temperature and water and
relevant to agriculture
– E.g. enzyme action, decomposition rate, carbon respiration, Nmineralisation
• SPECIES or DIVERSITY: can target specific groups
– Nematodes, earthworms, rhizobia, arbuscular mycorrhizal fungi,
DNA, community analysis, microbial functional (Biolog),
And INDIRECT
– E.g. Carbon fractions
Nematode Numbers
Root Knot Nematode density/kg dry soil
4000
Nematodes/kg dry soil
3500
3000
2500
Sep-09
2000
Mar-10
1500
1000
500
0
V1 control
V1 mulch
V2 control
V2 mulch
Sample date
V3 control
V4 mulch
Citrus Nematode
Citrus Nematode density/kg dry soil
Nematodes/kg dry soil
1200
1000
800
Sep-09
600
Mar-10
400
200
0
V1 control
V1 mulch
V2 control
V2 mulch
Sample date
V3 control
V4 mulch
Bacterial feeding Nematodes
Bacteria feeding nematode density/kg dry soil
Nematodes/kg dry soil
3000
2500
2000
Sep-09
1500
Mar-10
1000
500
0
V1 control
V1 mulch
V2 control
V2 mulch
Sample date
V3 control
V4 mulch
Predator Nematodes
Predator nematode density/kg dry soil
180
Nematodes/kg dry soil
160
140
120
100
Sep-09
80
Mar-10
60
40
20
0
V1 control
V1 mulch
V2 control
V2 mulch
Sample date
V3 control
V4 mulch
Other Free living nematodes
Other free living nematodes/kg dry soil
2000
Nematodes/kg dry soil
1800
1600
1400
1200
Sep-09
1000
Mar-10
800
600
400
200
0
V1 control
V1 mulch
V2 control
V2 mulch
Sample date
V3 control
V4 mulch
Examples of tests available
Pauline Mele Vic DPI
Test
simple
Cotton strip assay
Information
generalised
Decomposer potential
Fungi/bacteria ratio
Ecosystem health
Microbial biomass C/Total C
C turnover
CO2 Respiration
Overall soil microbial activity CO2
Earthworms (#/sp)
C levels, structure
Dung beetles
C incorporation
Cultivable Functional
Specific processes
Groups (eg cellulose degraders)
Microbial enzymes
Specific processes
BIOLOG™
Community catabolic diversity
DNA profiles
Community ‘fingerprints
Bacterial genes
Specific bacterial functions
Predicta B ™
DNA-based; for pathogens
Microarrays
1000’s genes (function & structure)
sophisticated
specific
Simple on-farm tests…
Looking for evidence of organisms:
• Calico strips - monitor
decomposition
• Set traps for macro and mesofauna e.g. ants
• Monitor dung beetles
• Look for worm casts >> earthworm activity
• Examine nodules on legumes
Soil biology – how (what) to
measure and monitor
Low biological
acitivity
Score: 0.5 / 4.0
High biological
activity
Score: 3.5 / 4.0
Casts at the soil surface are evidence that earthworms are shredding,
mixing, and burying surface residue.
Soil and Water Management Research Unit, USDA-Agricultural Research Service, St. Paul, Minnesota.
http://soils.usda.gov/sqi/concepts/soil_biology/
Simple on-farm tests…
Dig a hole deep enough so
that you can see the subsoil.
• Are the old inactive roots
decomposing? (bacteria and
fungi)
• Is there evidence of
bioturbation? (macrofauna,
e.g. earthworms and beetles)
• Does the soil smell “earthy”?
(actinomycetes)
• Is the soil dark in colour?
(SOC)
• Is the soil well-structured?
(soil aggregation)
Simple on-farm tests…
Assessing the soil environment
from soil properties and
chemical tests:
• SOC levels
• Subsoil colour (grey or mottling
indicates waterlogging)
• Soil chemistry: pHCa, salinity,
sodicity, toxicities.
• Structural problems:
compaction, erosion, or surface
crusting
Other:
• Groundcover assessment
What is most important when
using soil biological data?
1. Monitor –
see if the values are increasing or decreasing
over time.
2. Interpret from more than one set of
results
many readings from one site,
different times,
different types of information
3. Soil biological information is complex
interacts with whole environment: not many
generalities yet (but some emerging)
Carbon fractions are a good surrogate!!!