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
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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
!
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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)
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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)
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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
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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 ?
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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
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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
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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
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-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
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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
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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
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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