How do we estimate soil carbon levels
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Transcript of How do we estimate soil carbon levels
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How do we estimate soil carbon levels?
Making best use of existing science and knowledge
Brian Murphy
Cowra
November 2008
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Soil science knowledge that can help measuring and estimating soil carbon
Use known or developed relationships for soil properties to predict soil carbon levels
- Relationships between soil properties
- Relationships between soil properties and land management activities / practices
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Gaunaut report
“A comprehensive mitigation strategy will also require government intervention to promote abatement activity in sectors not covered by the emissions trading scheme. ………………………………………………………………..
The most significant opportunities may be in the area of improved carbon sequestration through better management of soil carbon.”
Measurement / estimate of soil carbon levels is Measurement / estimate of soil carbon levels is required for this to become effectiverequired for this to become effective
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1. Percentage soil carbon (C%)
- g carbon/100g soil
No volume taken into account
cannot be used for carbon accounting alone
2. Carbon density (CD)
- CD = C% x BD x soil depth
- t/ha
can be used for carbon accounting
requires measure of bulk density
requires depth to be specified
30 cm is the standard Kyoto depth.
Measuring soil carbon
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Changes in soil carbon density and changes in soil carbon content
0
5
10
15
20
25
30
35
40
45
0 1 2 3 4 5
Change in soil carbon content g/100g
Cha
nge
in s
oil c
arbo
n de
nsity
t/h
a
Soil carbondensity to 5cm
Soil carbondensity to 10cm
Poly. (Soilcarbondensity to 10cm)Poly. (Soilcarbondensity to 5cm)
On one paddock going from traditional tillage to long term pasture carbon % for 0 to 10 cm went from 1.20% to 1.92% over 15 years (10 cm), about 600 mm rainfall
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Bulk Density
Mass of soil solids per unit volume of soil- Usually taken as oven dry weight
Does not include the mass of water or air in the density calculation
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Soil surface
10 cm depth
Wheat root
Bulk density, mass of soil solids per unit volume
Soil pores can be filled by air or water
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Soil surface
Soil pores can be filled by air or water
Bulk density, mass of soil solids per unit volume
10 cm depth
Wild oats seed root
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Measuring Soil Carbon
Where to sample in the field
_what do we know?
What to measure in the field, how deep?_
_what do we know?
What to measure in the laboratory_
_what do we know?
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Where to sample in the field_Measuring Soil Carbon for Different Purposes
Scientific References Sites- Monitoring soil condition, testing or calibrating soil
carbon models
- 25 m grid or quadrat has many advantages from a scientific viewpoint
Estimating the soil carbon density of a paddock- Needs a different approach
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Soil analysed for soil carbon
1500 t soil/ha
10 kg soil collected?
0.1 to 0.5 kg sent to lab?
0.001 kg tested
Needs to be representative
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Selecting a representative sample in the field (based on fertiliser handbook)
Check target area for notable features that can influence soil type
– slope, drainage, soil colour, management history etc
Draw a sketch map and identify “individual areas” to be sampled. “Individual areas” should be uniform based on the above features. Satellite imagery and aerial photos can be very helpful
Avoid sampling across soil types and when soils are very wet
Take a number of cores and make into a composite sample for each “individual area”. Numbers of cores for a composite sample and the number of composite samples to characterise a paddock need to be determined.
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What to measure in the field, how deep? _ what do we know?
30 cm is the standard depth for carbon density.
Need to sample soils with a standard core so bulk density can be calculated
Care needs to be taken so that organic matter does not contaminate the soil samples below the surface
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What to measure in the laboratory _ what do we know?
Measure carbon content – treat with acid if carbonate present- LECO furnace – standard
- MIR spectrophotometer – quick and cheaper???
Measure soil moisture and weight to get bulk density.
Calculate carbon density (C% x bulk density) – a slight buffer to storing carbon / unit depth?
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Using Knowledge of Soil Relationships
What accuracy for soil carbon density, soil carbon % is acceptable ?
- ± 10t/ha, ± 1t/ha, ± 0.1 t/ha, ± 0.01 t/ha _ costs tend to increase exponentially with increased accuracy.
Use known or developed relationships for soil properties to predict soil carbon levels
- Relationships between soil properties
- Relationships between soil properties and land management activities
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Relationships between soil properties
Bulk density v soil texture, soil carbon and soil type
Soil carbon density to 10 cm and soil carbon density to 30 cm- Using soil carbon depth functions
Other????- MIR in the field
- Soil colour
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Wagga_LECO carbon levels g/100g
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5
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15
20
25
30
35
40
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00
LECO carbon levels g/100g
Dep
th (c
m) DD stubble retain
TT stubble retain
DD stubble burn
TT stubble burn
650 mm rainfall, red earths
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Changes in soil carbon density with clearing
0
10
20
30
40
50
60
70
80
90
100
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Soil carbon density (t/ha/cm of soil)
So
il d
epth
(cm
)
Uncleared
4 years
3 years
90 years
29 years
34 years
10 years
9 years
Rainfall 450 to 550 mm, red earths,Bimble Box
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Caution – likely to be soil type and climate specific!!!
Predicting soil carbon density to 30 cm using soil carbon density to 10 cm - based on NSW
Paired sites (Murphy et al. 2003)
y = 1.6546x + 7.3616
R20.929 =
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30 35
Soil carbon density to 10 cm t/ha
So
il c
arb
on
den
sity
to
30
cm
t/h
a
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Relationships between soil carbon levels and land management practices Many known relationships between land
management practices and soil carbon levels. Problem of continual developing and
improving land management practices Available data is scattered and does not
include all permutations and combinations However, modelling can be used to fill in the
gaps, with real data providing the benchmarks to work around
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t / ha / 30 cm
20
30
40
S* N* R* T*E*
annual average
evaporation
moderate
annual average rainfall
annual average
temperature 0C
1500 mm 25
long term nutrient levels
650 mm
Soil Carbon Potential
Soil texture, clay content
fine sandy loam (15%)
Land Management Practice
50
60
70
80
0
10
25
t / ha / 30 cmfine sandy
loam (15%)
Land Management Practice
50
60
70
long term nutrient levels
650 mm
Soil Carbon Potential
Soil texture, clay content
Long term perennial pasture
annual average
evaporation
moderate
annual average rainfall
annual average
temperature 0C
1500 mm 25
S* N* R* T*E*
80
0
10
20
30
40
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t / ha / 30 cm
20
30
40
S* N* R* T*E*
annual average
evaporation
moderate
annual average rainfall
annual average
temperature 0C
1500 mm 25
long term nutrient levels
650 mm
Soil Carbon Potential
Soil texture, clay content
fine sandy loam (15%)
Land Management Practice
50
60
70
Long term perennial pasture
Scalds
80
0
10
27
t / ha / 30 cm
Land Management Practice
50
60
70
0
10
Direct drilling with stubble burning (hot)
long term nutrient levels
650 mm
Soil Carbon Potential
Soil texture, clay content
annual average
evaporation
moderate
annual average rainfall
annual average
temperature 0C
1500 mm 25
N* R* T*E*
20
30
40
S*
fine sandy loam (15%)
Long term perennial pasture
Scalds
80
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t / ha / 30 cm
80
S*
fine sandy loam (15%)
Long term perennial pasture
Scalds
N* R* T*E*
annual average
evaporation
moderate
annual average rainfall
annual average
temperature 0C
1500 mm 25
Direct drilling with stubble burning (hot)
No till with stubble retention and
controlled traffic
long term nutrient levels
650 mm
Soil Carbon Potential
Soil texture, clay content
Land Management Practice
50
60
70
0
10
20
30
40
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t / ha / 30 cm
Land Management Practice
50
60
70
0
10
20
30
40
Direct drilling with stubble burning (hot)
No till with stubble retention and
controlled traffic
Annual pasture, volunteer pasture
long term nutrient levels
650 mm
Native vegetation - minimal disturbance
Soil Carbon Potential
Soil texture, clay content
annual average
evaporation
moderate
annual average rainfall
annual average
temperature 0C
Traditional tillage with multiple
cultivations and stubble burning
1500 mm 25
N* R* T*E*
80
S*
fine sandy loam (15%)
Long term perennial pasture
Scalds
30
Soil texture, clay content
annual average rainfall annual average
temperature 0C
Direct drilling with stubble burning (hot)
Scalds
1500 mm 25
60
Long term perennial pasture
No till with stubble retention and
controlled traffic
Direct drilling with stubble retention
long term nutrient levels
650 mm
Traditional tillage with multiple
cultivations and stubble burning
Soil Carbon Potential t/ha/30 cm
10
0
Annual pasture, improved pasture
Annual pasture, volunteer pasture
50
40
30
20
80
70
High nutrients . Low disturbance
S* N* R* T*E*
annual average evaporation
Native vegetation - minimal disturbance
fine sandy loam (15%) moderate
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Extra Information about land management practices to predict soil carbon levels.
Biomass and yields – use of fertilisers?
Stubble management – amount of stubble retained – not burnt (early hot v late cold burn), grazing
Soil disturbance, amount and type of tillage – threshold of tillage to start reducing soil carbon
Grazing intensity and timing of resting pasture – impact on biomass and plant growth
Species, grasses v herbaceous dicots
Perennial v annual – some knowledge yet to be gained.
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Conclusions 1
Methodologies to measure soil carbon are available - cost is the issue
Need to apply ALL existing soils knowledge and soil science to soil carbon issues
Exploring and investigating relationships between soil properties can bring down costs of measuring soil carbon
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Conclusions 2
Investigating the relationships between land management activities and soil carbon can be developed in a two step process
- Putting existing soil carbon measurements into a framework of climate x soil type x land management activities to give a soil carbon potential
- Using soil carbon models to fill in the gaps where there is no measured data.
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Chart Titley = -0.159x + 1.6046
R2 = 0.6666
0.90
1.00
1.10
1.20
1.30
1.40
1.50
1.60
1.70
0 0.5 1 1.5 2 2.5 3 3.5
BD
Linear (BD)
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Department of Environment & Climate Change NSW
First level dot point
- Second level dot point
Third level dot point
First level dot point
Soil carbon and available water - fine sandy loam mm/10 cm
0
5
10
15
20
25
0 1 2 3 4 5 6
Soil carbon g/100 g
Av
ail
ab
le w
ate
r m
m/1
0 c
m o
f s
oil
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Changes in soil carbon density and changes in soil carbon content
0
5
10
15
20
25
30
35
40
45
0 1 2 3 4 5
Soil carbon content g/100g
Cha
nge
in s
oil c
arbo
n de
nsity
t/h
a
Soil carbondensity to 5cm
Soil carbondensity to 10cm
Poly. (Soilcarbondensity to 10cm)Poly. (Soilcarbondensity to 5cm)
On one paddock going from traditional tillage to long term pasture carbon % went from 1.20% to 1.92% over 15 years (10 cm)