soil carbon: a viable offset strategy? · 2015-04-27 · what determines the carbon content of a...

Soil Carbon: A viable offset strategy? Dr. Jonathan Sanderman

Soil Carbon: A viable offset strategy?

Why Soil Carbon? The carbon cycle

Australia’s allocation of carbon Gt

Vegetation 18

Soil (0-1m depth) 48

GHG emissions (2007) 0.2


Why Soil Carbon? Sink capacity

Lal 2004 Science 304:1623

Globally, agricultural soils emitted ~200 Pg CO2 to the atmosphere

due to loss of soil organic carbon (40 – 60% decline in C stocks)

Sin

k c

apacity

Begin

cultivation

Management

shift


Why Soil Carbon? Functions in soil

Biological functions

- energy for biological processes

- reservoir of nutrients

- contributes to resilience

- cation exchange capacity

- buffers changes in pH

- complexes cations

Chemical functions Physical functions

- improves structural stability

- influences water retention

- alters soil thermal properties

Functions of SOM


Why Soil Carbon: The proverbial “win-win” situation

Building soil carbon stocks can both help mitigate climate change

and enhance food security through healthier, more productive soils

Lal 2004 Science 304:1623

Sin

k c

apacity

Begin

cultivation

Management

shift


Outline

1. Soil carbon basics

2. Agricultural influence on soil carbon

3. Accounting for changes in soil carbon

What is soil carbon?


Organic Carbon Inorganic Carbon

What is soil organic carbon?


Carbohydrates Amino Acids Phosphates Lignin

• Carbon is just the backbone of soil organic matter

• Soil OM is composed of1000’s of individual and often

uncharacterizable compounds

• Large quantities of nitrogen and phosphorous also

bound up in OM

What determines the carbon content of a

particular soil

• Dynamic balance of inputs and losses

• Inputs = plant residues, root exudates, mycorrhizal turnover,

manure and composts

• Net productivity is a function of climate, soil water, nutrients, etc…

• Losses = microbial decomposition, erosion, leaching

• Decomposition rate will be effected climate, soil type and

management

• Hot/dry places will have low carbon levels

• Cool/wet places will have high carbon levels


Carbon data reporting

Percentage v. Mass C mass (tonnes/ha) = Depth x %C x bulk density x gravel correction

% Carbon is usually only measured in the fine fraction

Actual claim: “total carbon increased from 0.75 to 2.0% in 1 year in a

broad acre cropping enterprise in the Riverina region”

In C mass terms, assuming a bulk density of 1.2, a 10 cm sampling

depth and no gravel, the C mass increased from 9 to 24 tonnes/ha. In

other words, 15 tonnes of C has been added to this soil in one year!

Compare to net primary productivity of, at best, 8-10 tC/ha/yr.

Be wary when people start saying they can increase soil carbon

levels by 1% in a few years time.


Distribution with depth and clay content


0 1 0 1 2 3 0 2 4 6

0

50

100

150

200

So

il D

ep

th (

cm

) Soil organic carbon content (% by weight)

0 1 2

Mallee

Sands

Red-

brown

Earths

Black

Earths Andisols

Clay content and presence of Fe and Al oxides

Soil Carbon - Carbon Trading Forum 29 Jan 2010

Composition of soil organic matter

Extent of decomposition

increases

Rate of decomposition

decreases

C/N/P ratio decreases

(become nutrient rich)

Crop residues on the soil

surface (SPR)

Buried crop residues

(>2 mm) (BPR)

Particulate organic matter

(2 mm – 0.05 mm) (POC)

Humus (<0.05 mm) (HumC)

Dominated by charcoal

with variable properties

Resistant organic matter

(ROC)

Years

Soil

org

anic

carb

on

0 10 20 30 40 50 60 70

TOC

Conversion to

permanent

pasture

Initiate

wheat/fallow

0

5

10

15

20

25

30

Why do we want to know about soil carbon

fractions?

33 15 43

HumC

ROC

POC

18 y 10 y

less humus C

more POC

Soil carbon levels tend towards equilibrium

Time

100

80

60

40

20

0

Control (no additions) Manure addition then stopped Manure addition maintained

Soil

org

anic

carb

on (

tonnes C

/ha)

Petersen et al. (2005) Soil Biol Biochem 37: 359

1. Sink capacity is finite

2. Most rapid changes in first 10-20 years

3. Sink is reversible if management is not maintained


Outline




0

2

4

6

8

10

12

14

16

1980 1982 1984 1986 1988

10 c

m S

OC

(t C

/ha)

Year

Conventional tillage (b = -0.51, P < 0.05)

Direct Drill (b = 0.09, n.s.)

Evidence for changes in soil carbon

Single point in time

comparison between

treatments

Soil

org

anic

carb

on

(Mg C

/ha)

Treat

2

Treat

1

50

75

25

Relative differences Absolute difference Repeat measurements

through time

Packer 1992

Impact of Australian agriculture on soil carbon:

relative and absolute rates of change

Min

25th

percentile

Median Max

75th

percentile

All data normalised to the 0-15 cm

soil layer

Sanderman et al. 2010. Soil Carbon Sequestration

Potential: A review for Australian agriculture. CSIRO

Technical report

Absolute rates of soil C change were

found to be less than relative values

1) Cropping systems

- -0.1 to -0.3 Mg C ha-1 yr-1

2) Conversion from crop to pasture

- +0.3 Mg C ha-1 yr-1

Relative change in SOC (tonnes C/ha/y) -0.5 0 0.5 1.5 1.0

Relative impacts of agricultural practice on soil

carbon: International evidence

Altered fertiliser

inputs

Manure inputs

Cultivated to grassland

Forages in rotations

Conservation tillage

No-till adoption

Hutchinson et. al. (2007) Agric. For. Meteorol. 142: 288-302

Improved grassland

management

Reduced fallow

0.0 0.4 0.6 0.8 1.0 1.2 0.2

Change in soil carbon (tonnes C ha-1 yr-1)

Perennials in grazing systems


SO

C (

Mg C

ha

-1)

-20

-10

0

10

20

30

40

50

C4

-C (

%)

0

10

20

30

40

Perennial pasture age (yr)

0 10 20 30 40 50

C4

-C (

Mg C

ha

-1)

0

5

10

15

20

25

SA - FP + KI

WA - ND

WA - SD

SO

C (

Mg C

ha

-1)

-20

-10

0

10

20

30

40

50

C4-C

(%

)

0

10

20

30

40

Perennial pasture age (yr)

0 10 20 30 40 50

C4-C

(M

g C

ha

-1)

0

5

10

15

20

25

SA - FP + KI

WA - ND

WA - SD

Study of subtropical grasses (kikuyu,

panic and Rhodes) in improved pastures:

• Kikuyu responsive but response

depends on soil type/region

• 0.3 to 0.6 tC/ha/yr increase in SOC

New studies starting July 2012:

• Rotational grazing to restore native

perennial grasses (CSIRO)

• Use of perennial fodder shrubs in

grazing systems (Future Farming CRC,

Rural Solutions SA)

Soil Carbon - Carbon Trading Forum 29 Jan 2010

Summary of management impacts on soil carbon

Cropping systems

Agronomic Improvements

Elimination of Tillage

Stubble Retention

Cover crops instead of bare fallows

More pasture phases in rotation

Organic matter additions

Retirement and restoration of

degraded land

Grazing systems

Agronomic Improvements

Improved grazing (cell grazing)

Shift to perennial grasses

Inclusion of perennial shrubs

Inc

rea

sin

g s

eq

ue

stra

tion

po

ten

tial

Summary of management impacts on soil carbon


Many agricultural soils have the capacity to store more carbon

Local climatic and soil conditions will always factor into the

ability of a particular area to sequester carbon

Despite a general lack of good scientific evidence:

Many management shifts within existing production systems

appear only capable of halting the decline in carbon stocks

Higher sequestration rates will likely be seen for more drastic

shifts in management

What about claims of much higher rates?

Pasture cropping, biological amendments, biochar, etc…

The jury is still out.

1. Near complete lack of data

2. Short-term changes can be misleading

3. Theoretical reasons to both support and refute claims


Image courtesy: www.winona.net.au


Outline




Carbon integrity standards

1. Can you measure and verify the change?

2. Is the practice additional?

3. Will the carbon be stored permanently?

4. Will there be any leakage?

Applying these principles to soil carbon is much more

difficult than for many other mitigation strategies


Emissions avoidance versus sequestration

• Numerous recent papers arguing that emissions avoidance is

almost always a better deal than sequestration projects

Example: Landfills emit methane

(business-as-usual)

• Flare the methane to CO2 and you have

reduced the GHG potential 23 times

• It is Additional (no incentive to do it

otherwise), Permanent (the CH4 is not

emitted), easily Verified (inspection/remote

sensing) and there are no Leakage issues

(more CH4 isn’t going to be emitted elsewhere

due to this project)

Measuring and verifying soil carbon change

• Soil carbon is naturally variable and rates of change are small

relative to this natural variability

• Direct measurement is time consuming and expensive

• Need for bulk density measurements

• Rapid and cost-effective tools are being developed

• Need for modelling


20

25

30

35

40

45

Perennial replicate #5

SOC (Mg C ha-1

to 30 cm)

31.0 43.7 37.7 31.7

38.7 32.8 27.2 46.5

32.2 40.2 24.7 29.6

30.8 33.1 40.6 36.6

Comparison against business as usual –

reason for modelling

0-3

0 c

m s

oil

org

anic

carb

on

(t C

ha

-1)

Duration of agricultural production

(yr)

0

20

40

60

80

100

0 10 20 30 40 50

34 t C/ha

Intensive agricultural

practice

14 t C/ha

“Carbon friendly”

Agricultural practice

Additionality of soil carbon projects

• Most management options to increase soil carbon will increase

productivity (and hopefully profitability), thus it is arguable that

soil carbon would ever meet the additionality requirement.

• It comes down to how the Australian government wants to

interpret additionality. The latest from the CFI website:

“The financial additionality test has been removed from the

legislation. Instead, abatement activities that are not common

practice in an industry or under specific regional conditions will

be deemed to meet the additionality test.”


Permanence of soil carbon

From Petersen et al 2005

1860 1900 1940 1980

100

80

60

40

20

0

Control (no additions) Manure addition then stopped Manure addition maintained

Soil

org

anic

carb

on (

Mg C

/ha)

Management changes

that build soil C must

be maintained to

maintain soil C

Soil C storage capacity is

finite and the largest

changes happen early

Soil C changes

take place over

long time periods

Petersen et al. (2005) Soil Biol Biochem 37: 359

Carbon Leakage

• Example 1: Soil carbon is enhanced by increasing use of

nitrogen fertilizer, but there would be an increase in nitrous

oxide emissions.

• Example 2: A humic acid extracted from coal to build soil

carbon levels, but there are emissions involved in the mining

and extracting phases.

• Example 3: If all Australian wheat growers shifted to permanent

pastures, an equal amount of land elsewhere in the world would

likely be brought into wheat production to meet the demand.

• It will be interesting how leakage plays out in the CFI.


Political versus atmospheric reality

Depending on how these integrity standards

are applied, there is a real risk that carbon

offsets may be generated that have no actual

impact upon atmospheric CO2 levels.


Summary

• Soil carbon levels are a result of a dynamic balance

between inputs and losses

• Modest gains in soil carbon appear attainable across

much of the agricultural sector

• Details of how we account of soil carbon in a trading

scheme still need to be finalised

Soil carbon will likely be part of the

solution, not the solution


Finally… Why biospheric offsets in the first place?

Stopgap measure to buy us a few decades of time to

transition away from a fossil fuel based economy.

Currently, this seems to have been completely forgotten

Otherwise, we just have an expensive program to

promote environmental sustainability.


Thank you

CSIRO Land and Water

Dr. Jonathan Sanderman

Carbon and Nutrient Cycling Group

Research Scientist

Phone: +61 8 8273 8135

Email: [email protected]

Contact Us

Phone: 1300 363 400 or +61 3 9545 2176

Email: [email protected] Web: www.csiro.au

soil carbon: a viable offset strategy? · 2015-04-27 · what determines the carbon content of a...

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