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Belinda Rawnsley
South Australian Research and Development Institute
(SARDI)
Soil biology
Healthy Soils and Carbon farming workshop June 2012
Introduction
• Why soil biology is important
• Tests to measure soil biology
• How and when to sample
• Improving soil biological health
Soil biology
• Break down organic matter and release nutrients into plant available forms
BAM!
Soil biology
• Break down organic matter and release nutrients into plant available forms
• Suppress soil borne diseases
• Improve and maintain soil structure
Soil biology
• Break down organic matter and release nutrients into plant available forms
• Suppress soil borne diseases
• Improve and maintain soil structure
• Degrade chemicals
• Lock up greenhouse gases in soil
A viable microbial population is essential for soil processes to occur
Soil biology
• Soil organisms change in abundance and
activity due to:
– Temperature
– Moisture
– Plant growth
• Not evenly distributed and occurs in 'hot-
spots' associated with soil organic matter
e.g. decomposing residues, the
rhizosphere and macroaggregates
Soil biological indicators
• Tests designed to measure activity or populations of soil organisms
• Routine soil tests do not measure soil biology
• Wide range of biological indicators to measure effect of soil management
Amount (e.g. microbial biomass, plate counts)
Activity (e.g. soil respiration, enzyme activity)
Diversity (e.g. community composition)
Microbial biomass
• Total population of active microbes in
the soil at the time of sampling
• Influenced by soil properties
• Measured by amount of carbon,
nitrogen, phosphorus and sulphur
• Responds quickly to changes in soil
management
• 1 to 5 % of total organic carbon (source DPIVic).
Microbial biomass and soil carbon
Lower than expected microbial biomass may indicate
a constraint to biological fertility
Source:Soilhealthknowledge.com.au
Seasonal variability of microbial
biomass in vineyards (Barossa Valley, 2009/2010)
0
5
10
15
20
25
30
35
40
Cultivated Biodynamic Permanent
sward
Mulch Grazing
land
To
tal m
icro
bia
l b
iom
ass (
ug
C/g
)
2 Nov 2009
1 Feb 2010
25 March 2010
HIGH
MODERATE
Method: Substrate Induced Respiration (SIR)
Fungi and bacteria
• Measured as a proportion of fungi and
bacteria in soil
• Fungi associated with decomposition and
soil structure stability
• High carbon requirement
• Bacteria regulate nutrient supply e.g.
transform nitrogen into a useable form
• High nitrogen requirement
Nematodes and mycorrhiza
• Beneficial role in the soil
• Free-living (saprophytic)
nematodes feed on bacteria
and fungi
– influence decomposition of
organic matter and nutrient
turnover
• Mycorrhiza fungi grow inside
the root and enhance vine
uptake of Phosphorus
Nematodes
No desired range
– ideal to use
nematode
abundance to
monitor change in
soil management
practice
Higher nematode
bacterial feeders
indicates low OM
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
Conventional
cultivation
Biodynamic Permanent sward Undervine mulch
no
. fr
ee
-liv
ing
ne
ma
tod
es
/20
0 g
so
il
Nov 2009
Feb 2010
Mar 2010
Some providers of soil health tests
Provider Cost Details
CSBP, WA $91 - $121 Microbiology tests, respiration
and direct counts
SWEP, Victoria $245 - $275 Microbiology test, cultural
based
Soil Foodweb, NSW $200 - $1500 Microbiology tests, cultural and
direct counts
Creation Innovation
Agriculture & Forestry,
SA
$50 - $250 Microbiology tests, molecular
based
Typical soil health test data
Total microbial
biomass (TMB) shows
population size of
microbes per g soil
Proportion of
fungi and
bacteria. Fungi % Protozoa,
nematodes
etc.
How to use soil biology tests
• There really are no target values for a
healthy soil in regards to soil biology
• Use tests to monitor changes in soil biology
over time at the same time of year
• Measure soil biology in relation to
management and/or problem areas
• Consider soil type, land use, topography
and plant growth - cannot compare regions
How to sample for soil biological
health
• Majority of organisms in top soil
and in the rootzone
• Bulk to give a representative
sample of the block (composite)
• Separate different areas
• Annuals – Sample planting row and
between the rows (on inter-row
spacing)
• Perennials – Sample in vine/tree row
– Under the drip line within 40 cm of
vine trunk or under tree canopy
Microbial activity at depth
0
20
40
60
80
100
120
140
0-5 5-10 10-20 20-30 30-40
Soil depth (cm)
B-g
luco
sid
ase e
nzym
e a
cti
vit
y
(m
g p
-Nit
rop
hen
ol/
kg
so
il/h
)
Rhizosphere soil
(Rawnsley, 2008)
When to sample
• Perennials – coincide soil sampling with
periods of peak root
growth from flowering to
post-harvest
• Annual crops – after crop harvest or
before seeding in autumn,
but before cultivation
– Sample closer to sowing to
reflect nutritional status
• Avoid directly after
application of soil
amendments or fertilisers
Shoot
growth
Root
growth
Monitor at the same
time of the year
Grapevine growth
Chemical use and soil biology
• Soil biology decompose chemicals and
pesticides – use them as a food source
• Impact of a pesticide depends upon the
rate of degradation
• Minimise use of heavy metals, e.g. copper
Soil Organic Carbon (SOC)
• Changes in soil organic carbon are slow
• Microbial populations change more rapidly
and reflect soil management
Barossa Valley (loam over clay)
Incorporated mulch* 1.8 %
Conventional cultivation 1.0 %
Permanent sward 0.8 %
Biodynamic 0.7 %
*Mulch applied in 2005
Soil organic matter is usually calculated as 1.72 x SOC
How to improve soil biology
• Feed the microbes!
• Organic matter must be continually supplied
How to improve soil biology
• No tillage, stubble retention
• Apply compost
• Use of covercrop and mulch
• Soil additives/amendments
• Use rotations
What about microbial
inoculants?
• If current practices have low microbial
populations, additions of new microbes or
organisms are unlikely to thrive and persist
– increase organic matter
• Products stimulate organisms already in soil
• Manage existing soil biology
• Legume inoculants proven
Soil health tests –
Take home message
• Use soil biological tests in conjunction with chemical and physical analysis
• Monitor soil health over time
– will reflect changes in soil management practices
• Monitor changes within a single block
• Low microbial biomass restrains nutrient
availability…build up soil biology
Acknowledgments
• NRM Board
• Barossa Viticulture Technical Group (BVTG)
• Sponsors of the Geoff Knight Viticulture Innovation Award
– Elders
– GrapeBarossa
– Barossa Grapegrowers’ Vine Selection Society
• Participating grape growers
• Dr Greg Walker (SARDI) for nematode assessment
More web information
• Soil health knowledge bank
Soilhealthknowledge.com.au
• Victorian Resources online >soil health
vro.dpi.vic.gov.au
Soil health factsheets
• soilquality.org.au