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Enhancing soil organic carbon (SOC) sequestration: myth or reality in Africa?

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On June 19, 30 CGIAR scientists, representing seven CGIAR Centers and six CGIAR Research Programs (CRPs), exchanged recent research findings and identified priorities for a future research agenda on soil carbon and climate change. The meeting was hosted by the CGIAR Research Programs (CRPs) on Climate Change, Agriculture and Food Security (CCAFS), Water, Land and Ecosystems (WLE) and Forests, Trees and Agroforestry (FTA). Rolf Sommer, senior scientist at CIAT and WLE, made this presentation.

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Enhancing soil organic carbon (SOC) sequestration: myth or reality in Africa?

  1. 1. Enhancing SOC sequestration: myth or reality in Africa? Rolf Sommer r.sommer@cgiar.org
  2. 2. From the FAO SOC 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
  3. 3. Losses of SOC in response to Land use (change) Source: Don et al. 2011 Global Change Biology 17, 1658–1670
  4. 4. 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/m²/10 to 12 cm Years since native forest conservation Heavy-textured North Nandi Heavy-textured South Nandi Medium-textured Kakamega
  5. 5. 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
  6. 6. 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
  7. 7. Observed SOC changes over time under "improved" land use Source: 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/kg) 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!
  8. 8. Observed SOC changes over time under "improved" land use Source: Don et al. 2011 Global Change Biology 17, 1658–1670
  9. 9. 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 content Time Improved management Common practice ?
  10. 10. 6/27/17 10 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
  11. 11. 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
  12. 12. • 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
  13. 13. 1 Thank you! Photo © A. Notenbaert

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