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12C

13C

14C

carbon

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12C

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14C

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Aspects of soil carbon mapping and monitoring via GlobalSoilMap

The spline model, material coordinate systems and aud iting soil carbon on farms

Alex McBratney, Budiman Minasny, Brendan Malone,Ichsani Wheeler & Sophie Gulliver

The University of Sydney AUSTRALIA

COP15

EU The Digital Soil Map of the World: its Relevance to UNFCC

EU Pavilion C5 Room Monnet December 12 2009

www.globalsoilmap.net

Soil Depth FunctionsSoil Depth Functions

• Variation of soil properties down a profile is continuous….though it is often represented as being discontinuous .

• Continuous soil depth functions include :

•free-hand drawing: no mathematical form

•exponential, regression and polynomial equations: can be

problematic

• smoothing splines: a better alternative

An equal-area quadratic spline from Ponce-Hernandez et al. 1986.

Raw soil data Fit spline function to raw data

Derive the mean estimate of carbon at specified depth intervals….user defined. These become the target inputs for modelling.

Carbon Storage

Fitted splines of

raw data

Fitted splines of

raw data

• Environmental

factors: Elevation,

slope, altitude above

channel network,

stream power index,

potassium, bands #3,

#4 and #5 and band

ratios 3/7 and 5/7

• Fit of model: R2

ranged between 50-

78%- best predictions

20-100cm

• Adequate fit of

predicted spline

functions with raw

profile data in most

Profile Soil C prediction

Carbon Storage

Fitted splines of

raw data

Fitted splines of

model estimates

Fitted splines of

model estimates

Fitted splines of

raw data

• Environmental

factors: Elevation,

slope, altitude above

channel network,

stream power index,

potassium, bands #3,

#4 and #5 and band

ratios 3/7 and 5/7

• Fit of model: R2

ranged between 50-

78%- best predictions

20-100cm

• Adequate fit of

predicted spline

functions with raw

profile data in most

Depth at

which soil C

< 1%

carbon density

(kg m-2 to 1m)

Total soil carbon density to 1m in

Edgeroi NSW

Mean value

?uncertainty?

carbon density

(kg m-2 to 1 m)

Total soil carbon density to 1m

Edgeroi NSWLOWER 99%

MEAN

UPPER 99%

858

774

738690

840

708

738

774

858

see Lee et al. (2009) Determining soil carbon stocks: Simple bulk density correction fail. Agriculture, Ecosystems, Environment 134 251-256

Spatial(length or depth) or material (mass) coordinate

system?Depth may be a troublesome unit of measure…

0.00

0.06

0.12

0.03

0.15

0.09

0.18

Dep

th (

m)

1.23

1.23

1.43

1.15

1.18

1.40

1.40

Unaccounted soil

Bulk density (Mg m-3)

132 Mg ha-1 not sampled

Time 1

i.e. tillage

0.18

0.21

0.00

0.06

0.12

0.03

0.15

0.09

Time 2Management event

738 Soil mass (Mg ha-1)

Sampled soil

1.15

1.18

1.40

Depth (m

)

Material coordinates

Spatial coordinates

+ 0.012 m

0

20

40

60

80

100

120

0 1 2 3 4

Dep

th (c

m)

C density (kg/m2)

0

20

40

60

80

100

120

0 5 10 15

Dep

th (c

m)

Cumulative C density (kg/m2)

Irrigated, annual crops

Dryland, annual cropsIrrigated,

annual crops

Dryland, annual crops

1500 kg/m21500 kg/m2

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4

Cum

ulat

ive

min

eral

mas

s (k

g/m

2)

C density (kg/m2)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 5 10 15

Cum

ulat

ive

min

eral

mas

s (k

g/m

2)

Cumulative C density (kg/m2)

Irrigated, annual crops

Dryland, annual crops

Irrigated,

annual cropsDryland, annual crops

1500 kg/m2

Soil depth to 1500kg/m2 mineral material

Total mass of carbon in 1500kg/m2 soil

material

Some sums:

Area ≈ 1700km2

Total mass of soil material (1500kg/m2) ≈ 2.6 Pg

Total mass of carbon ≈ 200 Kt

Carbon percentage ≈ 0.8%

Updating/Monitoring/Auditing

Edgeroi - Changes over time

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30

No. years in irrigated cultivation

Tot

al C

(da

gkg

-1)

C = 0.7 exp(-0.13 years) + 0.8

Odeh McBratney et al. (2002)

0

10

20

OM

1940 1950 1960 1970 1980 1990

YEAR

Org

an

ic m

att

er

(%)

The change in Organic matter content of soils in Sumatra , Indonesia

For the top 15 cm

A reduction from 57 t/ha (4.5% C in 1940)

to 25 t/ha (1.5% C in 1970)

Globalsoilmap for stratification

Land useSoil carbon

density to 30 cm

� 20 equal area

strata

� 3 sites per

stratum

� Cores taken to

30cm depth

� Duplicate

samples taken

at each site

� 60 x 2 samples

= 120 samples

Stratified random

sampling scheme

(StRS)

C densitySOC density (kg m-2) on Dimby Downs Total C density (kg m-2) on Dimby Downs

Strata accounted for:

� 68% of variation in SOC

� 65% of variation in total C

� 50% of variation in SIC

C stocks on the whole farm

9410458SRS equivalentsample size

1.561.730.96StRS efficiency

110 06791 47423 368Upper 95% Confidence Limit

98 86081 48210 604Lower 95% Confidence Limit

+ 6 603+ 4 996+ 6 38295% ConfidenceInterval

201152194Standard error

103 45686 68916 766Total C on whole farm

Total C (Mg C)

Organic C (Mg C)

Inorganic C (Mg C)

C estimation efficiency

110 067

Upper 95%ConfidenceLimit

96 860

Lower 95%ConfidenceLimit

+ 6 60395% ConfidenceInterval

201Standard error

103 456Total C on whole

farm

Individualsamples

Total C to 30 cm depth (Mg C)

Soil C

Let’s include it

Let’s map it

And monitor it

Let’s put it back

(+20% by 2020)

And keep it there