Potential of SA soils to store carbon
Tim Herrmann
Technical Advisor, Land Management
www.environment.sa.gov.au
Outline
• Role & types of carbon in soils
• Measurement of soil C
• What determines soil C levels
• Potential to increase soil C
www.environment.sa.gov.au
Estimated world carbon pools
Carbon pool
Vegetation
650 Gt
Atmosphere
750 Gt
Soil
1500 Gt
Ocean
39,000 Gt
1 Gt = 1 Giga t = 1 billion t =109 t
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On-farm C production (1200ha)
Ha
Biomass
(t/ha)
C
(t/ha)
C
(t/farm)
Cropping
1000
5
2
2000
Pasture
100
3
1.5
150
Native
vegetation
100
3
1.5
150
(av GY 2t/ha)
TOTAL
Grain only
2300
1000
2
0.9
900
900 t of C is equivalent to:
•
1.4 million litres petrol (or 1000 times around Australia)
•
3.3 million kWh electricity (or 460 households over 1 year)
•
11 million km air travel (or 340 return flights Adelaide-London)
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Role of organic carbon in soils
Engine room of a healthy and productive soil
• Biological
– energy, nutrient reservoir, resilience
• Physical
– structural stability, infiltration, water
holding capacity, thermal properties
• Chemical
– CEC, pH buffering, cation complexes
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Soil organic carbon pools
Fresh
Labile
Slow
- undecomposed material
Not part of soil C
- partly decomposed material
- microbial biomass
- humus
Recalcitrant
- charcoal
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Measurement of soil C
• Sampling protocols
• Depth
• 0-10 cm
• 10-30 cm
• Bulk density
• Paddock variability
• How often
• OC fractions
www.environment.sa.gov.au
Soil sampling grid – 10 samples
25m
X
X
X
25m
X
X
X
X
X
X
X
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How much carbon is in the soil?
Depth
Soil OC
(%)
Bulk
density
C
(t/ha)
0-10
1.4
1.4
20
10-30
0.35
1.4
10
TOTAL
30
To increase OC by 0.1% in top 10cm
 need 1.4 t C
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Organic carbon in soils
Soil OC = C inputs – C losses
C inputs:
• Determined by biomass production
• Driven by rainfall & management (eg burning, grazing, removal)
• Artificial inputs eg compost, biochar
C losses:
• Determined by management (eg soil disturbance, erosion)
• C storage capacity of soils determined by clay content
www.environment.sa.gov.au
Influence rainfall and texture on soil OC
12
Clay loam
10
Loam
S/loam
OC t/ha
8
Sand
6
4
2
0
300
400
500
600
700
800
900
1000
Rainfall (mm)
SA soils data from the Australian Soil Resource Information System
www.environment.sa.gov.au
On-farm C production (wheat crop)
Biomass
(t/ha)
C
(t/ha)
Management
C input (t/ha)
33% conversion
Grain
2
0.9
removed
Stubble
residue
3
1.2
50% grazed
Total roots
3
1.5
0.5
TOTAL
8
3.6
0.7
0.2
If soil OC is 1.0%, about 0.75 t of C is potentially lost through OM
turnover each year
This is matched by the estimated C input above
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Soil carbon project
• Collaborative project with CSIRO
• Part of the National Soil Carbon
Research Program
 Assess the potential for SA soils to
store carbon
 Determine the influence of
management practices on soil C
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Is there potential to store more carbon in soils?
„Graveyard plots‟ Wanilla (Univ of Adel)
•Established 1991
•Backhoe excavated “grave” plots
•Back filled to 1m with a range of treatments
•Significant differences in biomasswww.environment.sa.gov.au
production
Soil Organic Carbon (2002)
Wanilla “Graveyard plots" Trial
2.5
Walkley Black OC (%)
2
Control
Gypsum
1.5
Subsoil N,P,TE
Lawn Clippings
Topsoil
1
0.5
0
0 - 10
10 - 22
22 - 60
60 - 90
Depth (cm)
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Soil profile modification
Clay spreading and delving
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Influence rainfall and texture on soil OC
12
Clay loam
10
Loam
S/loam
OC t/ha
8
Sand
6
4
2
0
300
400
500
600
700
800
900
1000
Rainfall (mm)
SA soils data from the Australian Soil Resource Information System
www.environment.sa.gov.au
Soil profile modification
Spading
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Potential impact of soil profile modification
• Potential gain in the 0-30cms = 30 C t/ha
• Area of sandy soils in SA = 3.2 million ha
• If 50,000 ha modified each year
 potential to store extra 1.5 million t of C
 may take 10-15yrs to build up to this level
• If total 1 million ha modified
 potential to store extra 30 million t of C
• Net emissions from SA is 8 million t C per year
Note: would need to determine extra emissions from machinery
www.environment.sa.gov.au
www.environment.sa.gov.au