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The University of Sydney Page 1
Soil Carbon Modelling
Budiman Minasny Alex McBratney Jose Padarian
The University of Sydney Page 2
Background – Why the interest in soil carbon?
The University of Sydney Page 3
Soil carbon
The University of Sydney Page 4
Why Soil Carbon ‘Gold Rush’?
Soil C pool Organic C 1550 Pg Inorganic C 950 Pg
Atmospheric pool 760Pg
Biotic pool 610 Pg
Source: Lal (2006)
1 Pg = 1015 g = 1 billion ton
The University of Sydney Page 5
Paris Climate Change Conference
– Soil Carbon 4 per mille
8.9
2400= 4‰2400
Organic carbon stored in the soil globally
(up to 2 m)
Amount of C stock increaseneeded tooffset CO2emission
8.9
GlobalCO2 emissions from fossil fuels
billion tonne C
billion tonne C
The University of Sydney Page 6
Soil C 4 per mille
Agricultural practices that can sequester soil carbon
The University of Sydney Page 7
Soil C 4 per mille
The University of Sydney Page 8
– The need for better and more cost effective measurement of soil C – Auditing SOC – Modelling SOC – Monitoring SOC
The University of Sydney Page 9
Empirical models
The University of Sydney Page 10
Climate
Soil observations
DTM DEM
Remote Sensed Images
Existing Soil maps
scorpan layers Organic C: 0-5 cm
C = f(s,c,o,r,p,a,n) Spatial Soil
Prediction Functions
C stock Organic C: 5-15 cm
Organic C: 15-30 cm Organic C: 30-60 cm
Digital soil mapping
The University of Sydney Page 11
Digital soil mapping
9
0
40
0
Prediction Prediction variance
0 31.5 km
C stock
The University of Sydney Page 12
Sampling Design for Soil C Auditing
De Gruijter et al., 2016. Farm Scale Soil C Auditing. Geoderma.
The University of Sydney Page 13
Semi Empirical/Mechanistic models
The University of Sydney Page 14
Global Soil C Assessment
The University of Sydney Page 15
Global Soil C Assessment
– Models based on land cover change
– dC/dt = A – k. C
15
The University of Sydney Page 16
16
The University of Sydney Page 17
17
The University of Sydney Page 18
Process-based models
The University of Sydney Page 19
Struc-C
• There are influences and feedbacks between Soil Organic Carbon and soil structure
(e.g. Edwards and Bremner, 1967; Field, 2000; Kleber et al, 2007; Six et al., 2004) • Soil structure is rarely considered in soil carbon
models
◊ How does SOC influence the soil aggregation? ◊ Building a better structure (model)
The University of Sydney Page 20
FOM input Per month
RPM
DPM
CO2
CO2
AC 1
CO2 CO2
NCOC
AC 2
AC 3
CO2
CO2
BIO
HUM BIO
HUM
IOM
CO2
CO2
Decay
Decay
Decay
FOM input Per month
RPM
DPM
Coleman and Jenkinson, 1999
RothC
Struc-C
The University of Sydney Page 21
Aggregation
– The smallest aggregates are composed of organo-mineral associations. Strong clay to SOC bonds
– The clustering of these smaller aggregates forms larger aggregates, which in turn provides physical protection of the SOC between these aggregates from microbial attack.
The University of Sydney Page 22
Type 3
Type 2
Type 1
Forest to plantation
Plantation to cropland
The University of Sydney Page 23
The University of Sydney Page 24
100 200 300 400 500 6000
1
2
3
4
5
6
7
Years
SOC
(%) Type-3
Type-2
Type-1
NCOC
Tallgrass prairie Cropped Restored prairie
Simulation
The University of Sydney Page 25
Years since restoration
0 5 10 15 20 25 30 35 40 45 502
3
4
5
6
7
8
9
10
Years
Tota
l OC
(%)
0 5 10 15 20 25 30 35 40 45 50
0.7
0.8
0.9
1
1.1
1.2
1.3
YearsBu
lk d
ensi
ty (g
/cm
3)
The University of Sydney Page 26
0 5 10 15 20 25 30 35 40 45 500
10
20
30
40
50
60
Years
Aggregates(%)
0 5 10 15 20 25 30 35 40 45 500
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Years
C Ag
g(%
)Microaggregate C
Micro within macroaggregate C
Macroaggregate C
Microaggregate C
Micro within macroaggregate C
Macroaggregate C
The University of Sydney Page 27
Other models
– Carbon, aggregation, and structure turnover (CAST) , Stamati et al. 2013
AggModel, Segoli et al. 2013
The University of Sydney Page 28
Struc-C Improvement
– A better definition of Aggregate pools – Reconciling measured & modelled aggregates – Distribution with depth
FOM input Per month
RPM
DPM
CO2
CO2
Micro
CO2
NCOC
Macro
CO2
CO2
The University of Sydney Page 29
Soil C Landscape model
– 3D Soil genesis model, millennial time scale – C -> Simple 2 Compartment model, NPP production,
erosion, vertical mixing, productivity feedback
A quantitative model for integrating landscape evolution and soil formation T. Vanwalleghem, U. Stockmann, B. Minasny, A.B. McBratney. JGR
The University of Sydney Page 30
Soil-landscape model
The University of Sydney Page 31
Conclusions
– 4 per 1000: Soil C is relevant for mitigation of climate change – To achieve 4 per mille Soil C initiative, we need to be able to
measure it with confidence, model the C change & monitor it. – Soil C & structure still lacks a quantitative model. – Opportunities for greater collaboration