Belinda Rawnsley South Australian Research and Development Institute (SARDI) Soil biology Healthy Soils and Carbon farming workshop June 2012
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