Enhancing SOC sequestration:
myth or reality in Africa?
Rolf [email protected]
21 March 2017Rome, Italy
CGIAR Consortium
IFPRI
CIMMYT
CIP
BIOVERSITYINTERNATIONAL
AFRICA RICE IITA
ILRI
ICRAF
ICARDAICRISAT
IWMI
IRRI
CIFORWORLD FISH
ILRI
Placing Sustainability at the Heart of Agricultural Development
From the Symposium webpage:…large losses of soil organic matter …have occurred in soils from various global agroecosystems … where losses ranged between 25–75 % of their original SOC pool. These losses provide an opportunity: the recoverable carbon reserve capacity of the world’s agricultural and degraded soils is estimated to be between 21 to 51 Gt of carbon.
Soil organic carbon sequestration aspirations
How much is recoverable, where, and how long would it take and then last?
Total emissions worldwide
(2012) 51,840 Mt CO2 EQ
=
14.14 Gt C
Source: EcoFys 2016
Losses of SOC in response to Land use (change)
Source:Don et al. 2011 Global Change Biology 17, 1658–1670
Losses of SOC in response to Land use (change) Source: Kinjangi, 2008 (PhD thesis, redrawn)
Forest to cropland (Western Kenya)
0
2
4
6
8
0 30 60 90 120
kg C
/m²/1
0 to
12
cm
Years since native forest conservation
Heavy-texturedNorth Nandi
Heavy-texturedSouth Nandi
Medium-texturedKakamega
Losses of SOC in response to Land use (change)
Forest to permanent pastures (French Guiana Amazonia)
Pasture age (yrs)
Primary forest
Source:Stahl et al. 2016, Global Change Biology doi:10.1111/gcb.13573
Observed SOC changes over time under "improved" land use
In SSA increases were between 0.28 and 0.96 Mg C ha-1 yr-1, but with much greater variation and a significant number of cases with no measurable increase. …CA should be promoted on the basis of these factors and any climate change mitigation regarded as an additional benefit, not a major policy driver for its adoption.
… data from 125 on-farm validation trials across 23 sites in Malawi, Mozambique, Zambia and Zimbabwe. … No consistent differences in bulk density and soil C concentrations were found. … These results … indicate that there is a limited potential for conservation agriculture to significantly increase soil C stocks after up to 7 years of conservation agriculture
Observed SOC changes over time under "improved" land useSource: Sommer et al. submitted for publicationCIAT long-term trials, Western Kenya:
ISFM
17
19
21
23
25
1/Jan/05 1/Jan/08 1/Jan/11 1/Jan/14
SOC
(g/k
g)
FYM+ R+
FYM+ R-
FYM- R+
FYM- R-
LSD
Conservation Agriculture
17
19
21
23
25
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
Instead of C-sequestration, we detect losses in both systems!
Observed SOC changes over time under "improved" land use
Source:Don et al. 2011 Global Change Biology 17, 1658–1670
Food for thought• True C-sequestration or only "avoided losses"?• How transferrable are results to other tropical agro-ecosystems?• Importance of land use history!?• Importance of climate, "base" SOC levels / landscapes / clay
content and other soil properties…
SOC
cont
ent
Time
Improved management
Common practice
?
05/03/2023 13
A fundamental shift in global agriculture is required where sustainability constitutes the core strategy for agricultural
development.
Rockström et al. Ambio (2017) 46: 4. doi:10.1007/s13280-016-0793-6
Create the right enabling environment and incentives for change: policy and institutional
New systems and approaches: to motivate behavior change and enable the right responses
Innovation: to tackle new coincidences of problems
Multi-scale delivery that manages trade-offs and build synergies
Collaboration across research and development communities is key!
Moving from Opportunity to Reality: What’s needed?
Photo © G. Smith
• Revisit the individual "best bet" cases (above all grasslands)
• In sub-Saharan Africa food security and sustaining soil fertility comes first, SOC sequestration is a co-benefit only!
• Very different type of cropping systems are required for "carbon" farmers
• Avoid deforestation!
• Avoid draining wetlands and peatlands!
Holistic view
16
Thank you!Photo © A. Notenbaert
