carbon sequestration & sustainable farming in west african savannas: synergy or antagonism?

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Carbon sequestration & sustainable farmingin West African savannas: synergy or antagonism?G. Freschet1,2, R.J. Manlay1,2, Luc Abbadie3, B. Barbier4, C. Feller5, M. Leroy2, G. Serpantié6, and J.-L. Chotte1

1 IRD, UR179 SeqBio, Montpellier, France2 ENGREF, Dpt FRT, Montpellier, France3 ENS/CNRS, UMR 7618 BioEMCo, Paris, France4 CIRAD/TERA, UMR CIRED, Ouagadougou, Burkina Faso5 IRD, RU179 SeqBio, Antananarivo, Madagascar6 IRD, RU168, Antananarivo, Madagascar

13.07.2006

2

What is carbon sequestration ?

It is “[…] the net balance of all greenhouse gases […] computing all emissions sources at the soil-plant-atmosphere interface, but also all the indirect fluxes” (Bernoux et al., 2005)

Baseline

Project

timeBaseline GHG

emissionsProject GHG

emissions

GHG release

Baseline

Project

timeBaseline C stock

Project C stock

C accretion (storage)

C stock(tCeq)

Cumulated indirect GHG emissions(tCO2eq)

This is carbon sequestration

!

3

What is sustainable farming ?

A broad definition (FAO, 1989) : “one that, over the long term enhances environmental

quality and the resource base on which agriculture depends;

provides for basic human food and fibre needs;

is economically viable and

enhances the quality of life for farmers and society as a whole”

Is farming sustainable in West Africa ?

1000 km(kg ha-1 y-1)

30-60

>60

Nutrient depletion in Agricultural Lands of West Africa (2002-2004) (IFDC, 2006)

4

What are West African savannas ?

(Mayaux et al., 2004; Ardoin-Bardin, 2004)

0-200

200-400

400-600600-800

800-10001000-1200

1200-1400

Open grassland with sparse shrubsCroplands (>50%)Croplands with open woody vegetationOpen deciduous shrublandDeciduous woodland

Open grassland with sparse shrubsCroplands (>50%)Croplands with open woody vegetationOpen deciduous shrublandDeciduous woodland

Land cover and rainfall distribution across West African savannas

Isohyets for the 1969-1998 period (mean annual rainfall in mm)

5

Why sequester carbon in West African savannas ?

Because it is good for smallholders carbon is a multi-

purpose tool, both a valuable good and means of production

an indicator of the viability of low-input farming systems

carbon is an increasingly scarce resource

largely a scientific point of view from the NorthPaddy fields and palm grove in south Senegal

6

Why sequester carbon in West African savannas ? Because it is good for global society

Farming in the WAS, the global carbon cycle and global change

Carbon sequestration within the Clean Development Mechanism (CDM): several eligibility criteria

Other mechanisms exist: WB, GEF, CCX…

Again, a scientific discourse from the North

So, only win-win situations ?

7

But why so little C sequestration projects in West African savannas ? The facts

3 C sequestration projects in the pipeline:

– CDM-EB: 0– WB-BCF: 2– GEF: 1?– CBN: 0

Some reasons Uncertain economic

background Recent ratification

of the Kyoto Protocol

C sequestration conflicts with political issues

2006

≤2001

2002

2003

2004

2005

Not ratified (26.06.2006)

Mauritania

Mali

Niger

Nigeria

Benin

Tog

o

GhanaCôte

d’IvoireLiberia

Sierra Leone

Guinea

SenegalGambia

Cape Verde

Burkina FasoGuinea Bissau

White dots: no Designated National Authority

Year of ratificationof the Kyoto Protocolin West Africa

8

But why so little C sequestration projects in West African savannas ?

Working hypothesis There are heavy

biophysical and social barriers (other than weak institutional capacity)

that make C sequestration in the WAS much conflict-raising and uncertain

Millet harvest in manured fields south Senegal

9

Humification

manure

fire

leaching erosion,

senescence exsudation

senescence

respiration

Grain, forage

Litter Litter

Soil faunaand flora

AtmosphereAtmosphere

GrassAG

biomass

roots

GrassAG

biomass

roots

Tree

Above ground biomass

roots

Tree

Above ground biomass

roots

Fruits, wood, forage

Net primary production

Soil organic matter

How sequester carbon in West African savannas ?

Two major pools of the C cycle in the WAS Three management schemes examined as major sequestration options South-North, farmer-scientist hybridizations

Tree

Above ground biomass

roots

Tree

Above ground biomass

roots

Fruits, wood, forage

Agro-forestr

y

leaching erosion, Soil organic

matter

Conservation farming Fertilizatio

n

Grain, forage

Soil organic matter

Carbon flow

Carbon pool

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1. Soil fertilization

Objectives nutrient recapitalization SOC accretion Increased plant productivity

Strategy Mixed fertilisation: organic (manure,

compost, green manure) + mineral (urea, rock phosphate)

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Sequestration balance depends

on inclusion ofmanure-mediated

GHG release

1. Soil fertilization The Saria long-term trial: carbon

sequestration balance of soil fertilization in a ferric Acrisol of Burkina Faso

(adapted from Hien, 2002 ; Vlek et al., 2004 ; IPCC, 2006)

tCO2eq ha-1 40y-1

-120

-100

-80

-60

-40

-20

0

20

40

60

min fert MIN FERT min fert +manure

MIN FERT +MANURE

Carbon accretion in soil (0-40cm layer)

Mineral fertilizer synthesis & transport (release of CO2 and others)

Mineral fertilizer application (release of N2O)

Manure application (release of N2O)

N N N NPP

PPK

KK

K

0

50

100

150

0

50

kg nutrient

ha-1 y-1

tDM manure ha-1 y-1

Carbon accretion

requires mixed fertilization

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1. Soil fertilization The Saria long-term trial: impact of

soil fertilization on cereal yield in a ferric Acrisol of Burkina Faso

(adapted from Hien, 2002)

Relative increase

in sorghum

yield

N N N NPP

PPK

KK

K

0

50

100

150

0

50

kg nutrient

ha-1 y-1

tDM manure ha-1 y-1

0

1

2

3

4

5

6

7

8

min fert MIN FERT min fert +manure

MIN FERT +MANURE

No-input treatment = reference yield (abs. value = 335 kg ha-1)

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1. Soil fertilization Potential conflicts

Organic fertilizers needed possible competition with others uses of plant biomass (forage, construction, cash)

Risk management:– Low-cost SOC monitoring needs

homogenous practices– Variable agroecological conditions

requires diversified practices

If misconducted, fertilization can reduce soil carbon storage

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2. Conservation farming

Objectives Reduce soil loss by erosion and

leaching Increased plant productivity Improve soil biological status

Strategies No-till Mulching Cover crop

15

-30

-20

-10

0

10

20

30

40

50

60

70

Min fert Mucuna

0

1

2

3

4

5

6

Min fert Mucuna

2. Conservation farming Example: carbon accretion under no tillage

and cover crop on a Nitisol in Benin Baseline: maize with shallow weeding and no

synthetic fertilizer project: maize + no tillage + Mucuna cover crop

Sequestration balance

(tCO2eq ha-1 10y-1)

Relative increase in maize yield

(Azontondé et al., 1998; Barthès et al., 2004)

Carbon accretion in soil (0-40cm layer)

Mineral fertilizer synthesis & transport

Mineral fertilizer application

Mucuna application

No-input treatment = reference yield (abs. value = 301 kg ha-1)

Environmental benefit mostly

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2. Conservation farming Potential conflicts

Uncertainty about the CH4-N2O balance of cover crops

Weed control & equipment Communal land management:

common grazing habit conflicts with cover crop

Tillage abandonment: does it question the distribution of gender roles and balance ?

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3. Agroforestry Objectives

Increase the above-ground and below-ground plant C pools

Protect and increase the SOC pool

Strategies Simultaneous:

parklands, live hedges, (hedgerows),

Sequential: fallows, improved fallows

Afforestation/ reforestation: woodlots, wind breaks

Live hedge (right) and rangeland (left)in Futa Djalon, Guinea

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0

5

10

15

20

25

30

Short fallow(1-9 y)

Long fallow

Above-groundbiomass

Rootbiomass(0-40 cm)

Soil(0-40 cm ;fixed mass)

-20

-10

0

10

20

30

40

3. Agroforestry

Example: natural and improved fallow as sequential agroforestry systems

+27

+17

Natural fallow on a ferric Lixisol in Senegal: carbon accretion in the soil-plant system as compared to crop controls

Improved fallow on a ferric Acrisol in Togo: variation in the SOC (0-10 cm) amount after 5 years as compared to natural fallow controls

(recalculated from Manlay et al. 2002) (Drechsel et al. 1991)

C(tC ha-1 5y-1)

Natural woody fallow

Natural grass fallow

Huge variations between tree

species

High influence of the baseline scenario on the carbon balance of the practice

Most accretion occurs in biomass

C(tC ha-

1)

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3. Agroforestry

Potential conflicts Competition for resources

– Sharing light and water: conflict with the need for land ?

– Nutrients: priming effect hazard and SOC loss

Tenurial reform needed? Shift in balance of power between farmers, local decision-makers, and State

Uncertainty about the CH4-N2O balance of some perennial trees (inc. Leguminous such as Leucaena)

Need for fire control (A/R schemes)

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-3

-2

-1

0

1

2

3

4

5

6

7m

in fer

t

MIN

FER

T

min

fer

t +

man

ure

MIN

FER

T +

MAN

UR

E

MIN

FER

T

Mucu

na

Short

fal

low

(1-9

y)

Long fal

low

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

0

2

4

6

8

Barely predictable link between sequestration efficiency and agricultural value

1.Fertilization

2. Conservation

farming

Natural fallow Improved fallow

3. Agroforestry

Comparative overview: agricultural and environmental values of these case studies

Relative increase in

cereal yield (unitless)

Annual sequestration

balance (tCeq ha-1 y-1)

Agroforestry does better than soil management options, but…

Plant

Soil

Baseline: grass fallow

Baseline: woody fallow

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So… antagonism or synergy ?

C seques-tration option

C accretion in Improved OM recycling

soil tree biomass

Agro-ecological positive impact

Soil protectionRoot density

Wood availabilityForage availability

Crop yield in low-input systems

Water content

Soil protection

Soil biodiversity

Soil biodiversity & temperature

Soil biodiversity

Farmer’s perception

Scientific perceptio

n

1. Synergies on targets

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So… antagonism or synergy ?

C seq. option

C accretion in Improved OM recyclingsoil tree biomass

Resource needed

Synthetic fertilizer

Nutrient Light and water Crop residue Labour

Conflict Climate- related economical risk

Need for land (competition for light)Tenurial barrier

Crop residue as cash income

Need for labour-power at harvest time

Flexibility in cropping patterns

Flexibility in cropping patterns

Communal management of resources

Organic loss during transfers between plots

Priming effect hazard

Priming effect hazard

Tree-crop competition for water

Farmer’s perception

Scientific perception

2. Antagonisms on resource mobilization

Social issue Agroecological issue

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A pragmatic issue : how do carbon sequestration strategies complywith eligibility criteriato the Clean Development Mechanism ?

Eligible Agriculture, Forestry and Other Land Uses (AFOLU) activities

Additionality Biophysical Economical

Verifiability Risk management Compliance with host country’s

development strategy

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Enlarging our viewpoint: Reassessing the contributionof West African savannas to control the pool of atmospheric greenhouse gases

25

Mitigation strategies

Closing the nutrient cycle to decrease synthetic fertilizer use ? Wastes at the village level; N and P losses in a village of Senegal

– 1.9 kgN and 0.4kgP inhabitant-1y-1 = 15kgCO2eq ha-1y-1 or 8kgCO2eq inhabitant--1y-1

Low environmental potential but high agricultural interest of recycling human wastes

0

5

10

15

20

25

N

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

P

Village deficit

Loss in septic tank

kgN ha-1 y-1kgP ha-1 y-1

(Manlay et al. 2004b)

Nitrogen and phosphorus losses in the village of Sare Yorobana (1996-1997)

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Mitigation strategies

Livestock management Investing in

agriculture more than in cattle?

Improving cattle nutrition

Biofuel production

Carbon in crop residues is green gold: common grazing

on millet fields in south Senegal

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-4

-2

0

2

4

6

8

min

fer

t

MIN

FER

T

min

fer

t +

man

ure

MIN

FER

T +

MAN

UR

E

MIN

FER

T

Mucu

na

Short

fal

low

(1-9

y)

Long fal

low

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

(tCeq ha-1 y-1)

Annual sequestration balance & avoided deforestation

-3

-2

-1

0

1

2

3

4

5

6

7

min

fer

t

MIN

FER

T

min

fer

t +

man

ure

MIN

FER

T +

MAN

UR

E

MIN

FER

T

Mucu

na

Short

fal

low

(1-9

y)

Long fal

low

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

0

2

4

6

8Relative

increase in cereal yield

(unitless)

Annual sequestratio

n balance (tCeq ha-1 y-

1)

1.Fertilization

2. Conservation

farming

Natural fallow Improved fallow

3. Agroforestry

Baseline: grass fallow

Baseline: woody fallow

Mitigation strategies: including avoided deforestation in sequestration strategies

-4

-2

0

2

4

6

8

min

fer

t

MIN

FER

T

min

fer

t +

man

ure

MIN

FER

T +

MAN

UR

E

MIN

FER

T

Mucu

na

Short

fal

low

(1-9

y)

Long fal

low

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

Aza

d. i.

Alb

i. l.

Cass

ia s

.

Aca

c. a

.

(tCeq ha-1 y-1)

Annual sequestration balance

Avoided deforestation dramatically

increases the environment

al value of soil

management intensificatio

n

28

Efficiency accountancy Efficiency in energy, land and labour

resources in the West African savannas:one example from Senegal

02468

101214

Energy use: amount of energy required for food production

Land use: yield in standing biomass of

cereal cropsinput-kJkJ-1food

Sare Yoroban

a

United States

Sare Yoroban

a

European Union

0

2

4

6

8

10

12

(FAO 2006; Manlay et al. 2004ab; Steinhart and Steinhart, in Hall and Hall 1993)

tDMha-1

29

Conclusion Agricultural sustainability and carbon

sequestration: synergy or antagonism ? At the plot scale: pay attention to technical issues At the farm and village levels: examine social barriers Still much work for science!

Implementing carbon AFOLU projects in West African savannas eligible to the clean development mechanism ? a challenging job

Enlarged environmental strategies needed Conventional mitigation of course… … as well as avoided deforestation (still a hot issue

but…) Subsidize (yes!) African agriculture to keep it clean and

make it labour-efficient Support a more equitable, per-capita based approach to

efforts against climate change

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Thank you for your attention

Time for questions now !

Acknowledgmentsthis work was supported by the following institutions: Institute of Research for Development (IRD), RU 179

http://www.mpl.ird.fr/SeqBio/ Institute of Forestry, Agricultural and Environmental Engineering

(ENGREF), FRT, http://www.engref.fr Agricultural Research Centre for International Development (CIRAD),

http://www.cirad.fr National Center for Scientific Research (CNRS), RU Biomeco,

http://www.biologie.ens.fr/bioemco/ttp://www.cnrs.fr