the role of agricultural practices in keeping or ... · grazing land -...

The role of agricultural practices in keeping or increasing soil organic matter

Pete Smith

Professor of Soils & Global ChangeInstitute of Biological & Environmental SciencesSchool of Biological Sciences, University of Aberdeen,Scotland, UK. E-mail: [email protected]

Climate change – can soil make a difference? Brussels, Thursday 12th June 2008

PICCMATClimSoilCLIMATE CHANGE SOIL CARBON

Outline

• Soils in the global C cycle• Mechanisms for soil C sequestration • Global potential for soil C sequestration• Response of soil C sinks to future

climate change• Conclusions

Soils in the global C cycle

http://www.global-greenhouse-warming.com/global-carbon-cycle.html

Mechanisms for soil C sequestration

How does soil C sequestration work?

Organic carbon source

Add to soil

C in soil

CO2

Some C is stabilisedin the soil

Soil

Soil C cycle

e.g. residue management,organic amendments, increased plant C input…

Increase C inputs…e.g. restore & rewet farmedorganic soils

...or reduce C losses

– reduced disturbance

= microbe C = C inside aggregate

C

No-till

C

C

CC

C

C

TillageTillage breaksopen aggregates

= weatheringKey:

COrganic material (C)more exposed to microbial attack and weathering

How does soil C sequestration work?

Activity Practice Specific management change Increase C inputs

Decrease C losses

Reduce disturbance

Cropland management Agronomy Increased productivity XRotations XCatch crops XLess fallow XMore legumes XDeintensification XImproved cultivars X

Nutrient management Fertilizer placement XFertilizer timing X

Tillage / residue management Reduced tillage XZero tillage XReduced residue removal X XReduced residue burning X X

Upland water management Irrigation XDrainage X

Set-aside and land use change Set aside X XWetlands X X

Agroforestry Tree crops inc. Shelterbelts etc. X XGrazing land management Livestock grazing intensity Livestock grazing intensity X

Fertilization Fertilization XFire management Fire management XSpecies introduction Species introduction XMore legumes More legumes XIncreased productivity Increased productivity X

Organic soils Restoration Rewetting / abandonment X XDegraded lands Restoration Restoration X X X

Mechanisms for soil C sequestration in agriculture

Smith et al. (2007a)

Global potential for soil C sequestration

Method

• Database of over 200 experiments to derive per-area / per-animal mitigation efficiencies for >60 agricultural mitigation options, for four climate zones

• Mean estimates and low and high 95% CI values derived from mixed effects modelling

• Applied to appropriate agricultural (crop, grass) areas in each climate zone in each region


Tilla

ge F

acto

rs

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

No-Till

Reduced

TillageConventional

Tillage

1.0

9%

16%

Temperate MoistTemperate DryTropical MoistTropical Dry

3%

16%

10% 10%

23%

17%

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Res

pons

e R

atio

s

Reduced Till No-Till

Ogle et al. (2003)

Method




Smith et al. (2007a, 2008)

CO2 (t CO2 ha-1 y-1) CH4 (t CO2-eq. ha-1 y-1) N2O (t CO2-eq. ha-1 y-1) All GHG (t CO2-eq. ha-1 y-1)

Climate zone Activity PracticeMean

estimateLow High Mean



estimateLow High

Cool-dry Croplands agronomy 0.29 0.07 0.51 0.00 0.00 0.00 0.10 0.00 0.20 0.39 0.07 0.71Croplands nutrient management 0.26 -0.22 0.73 0.00 0.00 0.00 0.07 0.01 0.32 0.33 -0.21 1.05Croplands tillage and residue management 0.15 -0.48 0.77 0.00 0.00 0.00 0.02 -0.04 0.09 0.17 -0.52 0.86Croplands water management 1.14 -0.55 2.82 0.00 0.00 0.00 0.00 0.00 0.00 1.14 -0.55 2.82Croplands set-aside and LUC 1.61 -0.07 3.30 0.02 0.00 0.00 2.30 0.00 4.60 3.93 -0.07 7.90Croplands agro-forestry 0.15 -0.48 0.77 0.00 0.00 0.00 0.02 -0.04 0.09 0.17 -0.52 0.86Grasslands grazing, fertilizaltion, fire 0.11 -0.55 0.77 0.02 0.01 0.02 0.00 0.00 0.00 0.13 -0.54 0.79Organic soils restoration 36.67 3.67 69.67 -3.32 -0.05 -15.30 0.16 0.05 0.28 33.51 3.67 54.65Degraded landsrestoration 3.45 -0.37 7.26 0.08 0.04 0.14 0.00 0.00 0.00 3.53 -0.33 7.40Manure / biosol application 1.54 -3.19 6.27 0.00 0.00 0.00 0.00 -0.17 1.30 1.54 -3.36 7.57Bioenergy soils only 0.15 -0.48 0.77 0.00 0.00 0.00 0.02 -0.04 0.09 0.17 -0.52 0.86

Cool-moist Croplands agronomy 0.88 0.51 1.25 0.00 0.00 0.00 0.10 0.00 0.20 0.98 0.51 1.45Croplands nutrient management 0.55 0.01 1.10 0.00 0.00 0.00 0.07 0.01 0.32 0.62 0.02 1.42Croplands tillage and residue management 0.51 0.00 1.03 0.00 0.00 0.00 0.02 -0.04 0.09 0.53 -0.04 1.12Croplands water management 1.14 -0.55 2.82 0.00 0.00 0.00 0.00 0.00 0.00 1.14 -0.55 2.82Croplands set-aside and LUC 3.04 1.17 4.91 0.02 0.00 0.00 2.30 0.00 4.60 5.36 1.17 9.51Croplands agro-forestry 0.51 0.00 1.03 0.00 0.00 0.00 0.02 -0.04 0.09 0.53 -0.04 1.12Grasslands grazing, fertilizaltion, fire 0.81 0.11 1.50 0.00 0.00 0.00 0.00 0.00 0.00 0.80 0.11 1.50Organic soils restoration 36.67 3.67 69.67 -3.32 -0.05 -15.30 0.16 0.05 0.28 33.51 3.67 54.65Degraded landsrestoration 3.45 -0.37 7.26 1.00 0.69 1.25 0.00 0.00 0.00 4.45 0.32 8.51Manure / biosol application 2.79 -0.62 6.20 0.00 0.00 0.00 0.00 -0.17 1.30 2.79 -0.79 7.50Bioenergy soils only 0.51 0.00 1.03 0.00 0.00 0.00 0.02 -0.04 0.09 0.53 -0.04 1.12

Warm-dry Croplands agronomy 0.29 0.07 0.51 0.00 0.00 0.00 0.10 0.00 0.20 0.39 0.07 0.71Croplands nutrient management 0.26 -0.22 0.73 0.00 0.00 0.00 0.07 0.01 0.32 0.33 -0.21 1.05Croplands tillage and residue management 0.33 -0.73 1.39 0.00 0.00 0.00 0.02 -0.04 0.09 0.35 -0.77 1.48Croplands water management 1.14 -0.55 2.82 0.00 0.00 0.00 0.00 0.00 0.00 1.14 -0.55 2.82Croplands set-aside and LUC 1.61 -0.07 3.30 0.02 0.00 0.00 2.30 0.00 4.60 3.93 -0.07 7.90Croplands agro-forestry 0.33 -0.73 1.39 0.00 0.00 0.00 0.02 -0.04 0.09 0.35 -0.77 1.48Grasslands grazing, fertilizaltion, fire 0.11 -0.55 0.77 0.00 0.00 0.00 0.00 0.00 0.00 0.11 -0.55 0.77Organic soils restoration 73.33 7.33 139.33 -3.32 -0.05 -15.30 0.16 0.05 0.28 70.18 7.33 124.31Degraded landsrestoration 3.45 -0.37 7.26 0.00 0.00 0.00 0.00 0.00 0.00 3.45 -0.37 7.26Manure / biosol application 1.54 -3.19 6.27 0.00 0.00 0.00 0.00 -0.17 1.30 1.54 -3.36 7.57Bioenergy soils only 0.33 -0.73 1.39 0.00 0.00 0.00 0.02 -0.04 0.09 0.35 -0.77 1.48

Warm-moist Croplands agronomy 0.88 0.51 1.25 0.00 0.00 0.00 0.10 0.00 0.20 0.98 0.51 1.45Croplands nutrient management 0.55 0.01 1.10 0.00 0.00 0.00 0.07 0.01 0.32 0.62 0.02 1.42Croplands tillage and residue management 0.70 -0.40 1.80 0.00 0.00 0.00 0.02 -0.04 0.09 0.72 -0.44 1.89Croplands water management 1.14 -0.55 2.82 0.00 0.00 0.00 0.00 0.00 0.00 1.14 -0.55 2.82Croplands set-aside and LUC 3.04 1.17 4.91 0.02 0.00 0.00 2.30 0.00 4.60 5.36 1.17 9.51Croplands agro-forestry 0.70 -0.40 1.80 0.00 0.00 0.00 0.02 -0.04 0.09 0.72 -0.44 1.89Grasslands grazing, fertilizaltion, fire 0.81 0.11 1.50 0.00 0.00 0.00 0.00 0.00 0.00 0.81 0.11 1.50Organic soils restoration 73.33 7.33 139.33 -3.32 -0.05 -15.30 0.16 0.05 0.28 70.18 7.33 124.31Degraded landsrestoration 3.45 -0.37 7.26 0.00 0.00 0.00 0.00 0.00 0.00 3.45 -0.37 7.26Manure / biosol application 2.79 -0.62 6.20 0.00 0.00 0.00 0.00 -0.17 1.30 2.79 -0.79 7.50Bioenergy soils only 0.70 -0.40 1.80 0.00 0.00 0.00 0.02 -0.04 0.09 0.72 -0.44 1.89

Per-area / per-animal mitigation potential

For 14 practices, for 4 climate zones, for CO2, N2O & CH4, estimates for mean and +/- 95%CI Smith et al. (2007a)

-4 -2 0 2 4 6 8

Cropland - agronomy

Cropland - nutrients

Cropland - tillage&residue

Cropland - water

Cropland - setaside&LUC

Cropland - agroforestry

Grazing land -nutrient&grazing&species

Degraded land restoration

Manure application

Sequestration underenergy crops

Practice

CO2 sink (t CO2 ha-1 yr-1) Soil C sequestration rates for cool dry clim

ate

Data from

: Smith et al. (2007a)

-4 -2 0 2 4 6 8

Cropland - agronomy



Cropland - water





Manure application


Practice

CO2 sink (t CO2 ha-1 yr-1)

-2 -1 0 1 2 3 4 5 6 7 8

Cropland - agronomy



Cropland - water





Manure application


Practice


Dry

Moist

CoolWarm

-4 -2 0 2 4 6 8

Cropland - agronomy



Cropland - water





Manure application


Practice


-2 -1 0 1 2 3 4 5 6 7 8

Cropland - agronomy



Cropland - water





Manure application


Practice


Soil C sequestration rates in different clim

ates

Data from


Soil C emission reduction rates for organic soil restoration

0

20

40

60

80

100

120

140

160

Cool climates - Organic soil restoration Warm climates - Organic soil restoration

Practice

CO

2 sin

k (t

CO 2

ha-1

yr-1

)

Data from: Smith et al. (2007a)

Organic soil restoration vs. m

ineral soil sequestration

-20 0 20 40 60 80

100

120140

160

Cropland - agronomy



Cropland - water





Manure application


Organic soil restoration

Practice


Data from


Method




Smith et al. (2007a, 2008)

IPCC AR4 Agricultural GHG MitigationFAO AEZ Database (e.g. showing regions)

IPCC AR4 Agricultural GHG MitigationFAO AEZ Database (e.g. showing thermal climate)

IPCC AR4 Agricultural GHG MitigationFAO AEZ Database (e.g. showing production constraints)

IPCC AR4 Agricultural GHG MitigationFAO AEZ Database (e.g. showing land cover)

Global m

itigation potential in agriculture

-200 0

200

400

600

800

1000

1200

1400

1600

Cropland management

Water management

Rice management

Setaside, LUC &agroforestry

Grazing landmanagement

Restore cultivatedorganic soils

Restore degradedlands

Bioenergy (soilscomponent)

Livestock

Manure management

Mitigation m

easure

Global biophysical mitigation potential (Mt CO2-eq. yr-1)

N2O

CH

4C

O2


-200 0

200

400

600

800

1000

1200

1400

1600

1800

Southeast Asia

South America

East Asia

South Asia

Eastern Africa

Russian Federation

North America

Western Europe

Western Africa

Central Asia

Northern Europe

Middle Africa

Eastern Europe

Oceania

Southern Europe

Central America

Northern Africa

Western Asia

Southern Africa

Carribean

Japan

Polynesia

Region

Mt CO2-eq. yr-1


High and low

estimates of the

mitigation potential in each region

Effect of C price on im

plementation


0

200

400

600

800

1000

1200

1400

Restore cultivatedorganic soils

Croplandmanagement

Grazing landmanagement

Restore degradedlands

Rice management

Livestock

Setaside, LUC &agroforestry

Manuremanagement

Measure

Mt CO2-eq. yr-1

up to 20 USD

t CO

2-eq.-1up to 50 U

SD t C

O2-eq.-1

up to 100 USD

t CO

2-eq.-1

Global mitigation potential in agriculture (Mt CO2-eq. yr-1)

Price range (USD t CO2-eq. -1)

Scenario 0-20 0-50 0-1000->>100 (technical

potential)

B1 1925 2384 3149 5480

A1b 1982 2439 3254 5670

B2 2047 2495 3330 5844

A2 2119 2549 3330 5957

Smith et al. (2007a, b)Over 70% of the potential is in developing countries

Energy supply

0

1

2

3

4

5

6

7

<20 <50<10

0

<20 <50<10

0

GtCO2-eq

Transport Buildings Industry Agriculture Forestry Waste

Non-OECD/EITEITOECDWorld total

US$/tCO2-eq

Global economic mitigation potential for different sectors at different carbon prices

IPCC WGIII (2007)

How important is this C sequestration potential?

• Even at 100 USD t CO2-eq.-1, sequestration potential is 3100-3300 Mt CO2-eq. yr-1

• This is equivalent to less than 1000 Mt C yr-1

or <1 Pg per year• Atmospheric CO2-C is increasing at a rate of

3.2 Pg C yr-1 so soil C sequestration can mitigate less than 1/3 of this increase and less than 1/7 of fossil fuel C emissions

• So is it worth using C sequestration at all?

Why use C sequestration?

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IPCC TAR WGIII (2001)

The energy / emission gap under different SRES scenarios

• Current yearly atmospheric C increase = 3.2 ± 0.1 Pg C y-1

• Emission gaps of up to 25 Pg C y-1 by 2100 Smith (2004)

Why use sequestration?

Critical period determining trajectory IPCC (2001)

Response of soil C sinks to future climate change

Uncertainty in cropland & grassland SOC stock changes due to climate, NPP & technology change

70

75

80

85

90

95

100

105

110

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080

Year

SOC

stoc

k (t

C h

a-1)

Cropland

Grassland

70

75

80

85

90

95

100

105

110

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080

Year

SOC

stoc

k (t

C h

a-1)

(HadCM3-A2)

Climate Only Climate & NPP Climate & NPP & TechMinimumMaximum

J.U. Smith et al. (2005)

Uncertainty onAnthropogenic Carbon

Emissions

Up to ~450 ppm

Friedlingstein et al. 2006 IPCC SRES 2000

Vulnerability of the Carbon Cycle in the 21st century

Up to ~250 ppm

Uncertainty of theBiospheric-Carbon-Climate

Feedback

Slide courtesy of Pep Canadell, GCP

Conclusions• Soil C sequestration is a globally significant

climate mitigation measure• Soil C sequestration is cost competitive with

climate mitigation measures in other sectors• But - soil C sequestration is not permanent and is

of limited duration (due to sink saturation)• Response of soil C sinks to future climate change

remains uncertain• Protecting large soil C stocks (e.g. peatlands) is

very important for avoiding emissions

Thank you for your attention

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