SESSION 3 – THE FOUR PILLARS:
IV. CONTRIBUTION TO GLOBAL MITIGATION
Scaling up soil carbon enhancement
contributing to mitigate climate change
Rolf Sommer, Kristin Piikki, Mats Söderström,
Sylvia Nyawira, Mayesse da Silva,
Wuletawu Abera and
Job Kihara
r.sommer@cgiar.org
The 4 per 1000 Africa Symposium - Building
synergies across Africa to advance on soils for
food security and climate, Johannesburg, South
Africa 24-26 October 2018

"If you torture the data long enough,
it will confess to anything!“
Ronald Coase, Economist, Nobel Price laureate 1991 (Economics)
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CGIAR Centers

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CIAT around the world

Connected thinking, compelling solutions
WLE is a global research-for-development program connecting partners to
deliver agriculture solutions that enhance natural resources – and the lives
of people who rely on them
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Significant support from BMZ and GIZ!
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https://www.giz.de/en/worldwide/
32181.html

Soil organic carbon sequestration – rationale
Agriculture is a major
contributor to climate change!
• Ag production : ~12 %
• Land use change: ~12 %
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Agriculture, Forestry
and
Other Land Use
(AFOLU)
Greenhouse gas emissions by economic sector
(IPCC AR5)
Total emissions worldwide (2012)
14.14 Gt C
Source: EcoFys 2016

Soils contain massive
amounts of carbon, i.e.
little changes can make a
big difference!
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Carbon pool Amount (billion
tons C)
Ocean ~39,000
Atmosphere 785
Biotic 466 – 835
Geologic (coal, gas oil) 4,000 – 5,000
Soil, organic carbon 1,220 – 1,550
Soil, inorganic carbon 750 – 950
Soil, total (1 m depth) 2,000 – 2,500
Soil organic carbon sequestration – rationale

1. Large losses of soil organic matter
have occurred in agricultural soils
2. These losses provide an
opportunity
3. The recoverable carbon reserve
capacity of the world’s agricultural
and degraded soils is estimated to
be between 21 to 51 Gt of carbon
(FAO, 2017)
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(Sommer et al. 2018)
Soil organic carbon sequestration – rationale

Enhancing soil carbon
improves soil fertility, soil
health and helps increasing
agricultural productivity and
resilience!
Soil organic carbon sequestration
– rationale

Scaling up soil carbon enhancement
contributing to mitigate climate change
1. What could be achieved in
terms of climate change
mitigation?
2. What practices?
3. Where?
4. What is required to make it
happen?
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1. What could be achieved in terms of
climate change mitigation?
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Dynamics and climate change mitigation potential
of SOC sequestration (Sommer & Bossio, 2014)
SOC sequestration follows a
saturation curve
+
Uptake of improved practices
does take time
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• The projected 87-year (2014-2100) global
SOC seq. potential of agricultural land ranged between 31 and 64 Gt. (0.36 to 0.74 Gt/yr)
• Global climate change mitigation potential:
• 1.9-3.9 % of the SRES-A2 projected 87-year anthropogenic emissions
• 10-21 % of 4p1000 target
=

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Zomer, Bossio, Sommer, Verchot (2017) Nature Scientific Reports, doi:10.1038/s41598-017-15794-8
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Geospatial estimation of the global sequestration
potential of increased organic carbon in cropland
Worldwide croplands could
sequester between
0.90 and 1.85 Gt C/yr,
= 26–53 % of the target of
4p1000
But, unlikely to happen that
way…!

CIAT-GIZ Infographic
Tropical soils can
help us make
agriculture carbon
neutral and meet
climate targets!
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2. What practices?
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The impact of Conservation Agriculture
• Significant differences
between CA and business-
as-usual (BAU) in the top
20 cm: ~7.5 t C/ha
• CA practiced between 8-15
years, i.e. avoided SOC loss
or sequestration rates:
~0-5 – 0.9 t C/ha/yr
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Topsoil (0 - 20 cm) Subsoil (20 - 40 cm) 0-40 cm
CA BAU CA BAU CA BAU
25
50
75
100
10
20
30
40
50
10
20
30
40
50
Land management
SOC(Mg/ha)
lulc
BAU
CA
a b a a a b
* **
Western Kenya, Bungoma County
Different letters indicate statistically significant differences: * at P < 0.05; ** at P < 0.10
(Sommer et al. 2018)

Avoiding C-losses but failing to sequester…!
2. Land use history seems the major
driver of losses!
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ISFM
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23
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1/Jan/05 1/Jan/08 1/Jan/11 1/Jan/14
SOC(g/kg)
FYM+ R+
FYM+ R-
FYM- R+
FYM- R-
LSD
Conservation Agriculture
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19
21
23
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1/Jan/05 1/Jan/08 1/Jan/11 1/Jan/14
0T R+
CT R+
CT R-
0T R-
LSDs, same
level of tillage
CIAT long-term trials, Western Kenya – observed SOC changes over time under improved land use
1. Instead of C-sequestration, we
detect losses!
Source: Sommer et al. 2018
Avoided losses: ~0.1-0.7 t C/ha/yr

3. Where?
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Developing the predictive capacity to quantify the
impact of improved land management
• Pedotransfer function to predict
SOC under CA using: clay, silt,
sand; relative slope; valley depth;
elevation; wetness index; cross-
sectional curvature; aspect
(Sommer et al. 2018)
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SOCCA [g/kg] = - 4.033 + 0.0141*clay -
8.571*rel. slope pos. - 0.0018*valley
depth + 0.0049*elev. - 0.227*w. index
• A boundary plane approach to map
hotspots for soil carbon seq. potential
(Piikki et al. submitted):
𝑧 = a +
𝑏
𝑥
+
𝑐
𝑦
+
𝑑
𝑥𝑦

SOC sequestration hotspot mapping
• Digital soil mapping of
actual and potential SOC
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Western Kenya, Murugusi Watershed
(Sommer et al. 2018)

Potential changes in SOC in response to an adoption of CA
• Wide variation in
estimated gains
• Coarse-textured soils
and soils with high SOC
may lose carbon
• Total SOC seq. on all
cropland (6582 ha):
131,000 t C
(~20 t C/ha)
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(Sommer et al. 2018)

4. What is required to make it happen?
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Impact pathway
• Stakeholder engagement, stakeholder
engagement, stakeholder
engagement…!
• Agreed-upon priority intervention
regions, and scientific/institutional
alignment
• Assessment of tradeoffs, as well as
PES to endorse SOC-seq in smallholder
farming systems and rangelands
• Do we need thorough biophysical
monitoring, or can PES be implemented
based only on the adoption of good
agricultural practices?
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• The Kenya Agricultural Carbon
Project (KACP)
• Aim:
• The project promotes Sustainable
Agricultural Land Management (SALM)
practices for implementation on
smallholder farms for livelihood
improvement and generation of GHG
removals through soil and tree carbon
sequestration.
• BioCarbon fund payments from WB
• The resulting carbon credit is considered a
co-benefit and paid to farmer groups as
rewards
Achievements: 2009 to date
• 29,497 farmers in 1730 farmer groups
• 21,966 ha under SALM,
• 30-50 % higher maize yields,
• more months of food self-sufficiency
• higher level of monthly savings
Carbon:
184,447 t CO2e
(verified and farmers paid carbon)
Source: Miriam Nalianya, Vi Agroforestry

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Thank you!
Photo © A. Notenbaert

CIAT Team
Rolf Sommer, Mayesse da Silva,
Mats Söderström, Kristin Piikki,
Job Kihara, Birthe Paul,
Andrew Margenot, John Mukalama,
John Mutua, Wuletawu Abera,
Lulseged Tamene, Tesfaye Yaekob,
Evan Girvetz