Challenges of soil organic carbon sequestration in drylands
Dr. Rachid MRABETProf. Mohamed Badraoui
Dr. Rachid MoussadekProf. Brahim Soudi
FAO (Rome) Tuesday Mars 21st, 2017
The largest biome on Earth
41.3 % of the Earth’s continental area (430 Millions ha) and is expanding.38% of the world’s population (2.5 billion inhabitants).
84% of world cultivated area.67% of the world's food production.
Hotspots are sub-Saharan Africa (the Sahel, the horn of Africa and South-East Africa) and Southern Asia.
Global Map of drylands
No clear boundary
Hyper-arid (AI < 0.05) Arid (0.05 ≤ AI < 0.2)Semiarid (0.2 ≤ AI < 0.5) Dry subhumid (0.5 ≤ AI < 0.65)
Temporal variation in the aridity index and the areal coverage of drylands
Predictions include a growth in the land mass of dryland ecosystems by 11 to 23 % before the year
2100.
Huang et al. 2015
Carbon mass per hectare in the drylands
United Nations, 2011
Annual Global Primary Production as a function of the AI (Huang et al. 2015)
Dryland degradation & Sparse vegetation cover Droughts and desertification threaten the
livelihoods and well-being of more than 1.2 billion people in 110 countries
Prevent the aggravation of global desertification
Source: Global assessment of human induced soil degradation (Glasod) http://www.isric.org/projects/global-assessment-human-induced-soil-degradation-glasod; http://passthrough.fw-notify.net/download/341043/http://www.unep.org/maweb/documents/document.291.aspx.pdf
One and half billion people are dependent on degrading land.
Ten to twenty per cent of drylands are degraded.
Grand Challenges
Wide range of climates spanning from hot to cold
Land use systems in the drylands
FAO “Draylands, People and Land use” http://www.fao.org/docrep/012/i0372e/i0372e01.pdf; http://passthrough.fw-notify.net/download/341043http://www.unep.org/maweb/documents/document.291.aspx.pdf
Source: http://www.eoearth.org/view/article/152297/; http://www.un.org/en/events/desertification_decade/whynow.shtml
Supporting 50% of the world’s livestock, rangelands – vast natural landscapes - are habitats for wildlife.
Due to climate change, the area covered by rangelands will grow.
Dryland characteristics that unfavor carbon sequestrationClimate significantly influences large-scale patterns of soil carbon sequestration:
• Lack of water (low water availability)• Low and erratic rainfall (chronic
shortage of soil moisture)• Brief periods or pulses of water
sufficiency • High temperatures (amplitudes) Soil
respiration (mean annual temperature greater than 30°C)
• Cold temperatures (mean annual temperature less than 20°C).
Pulse-reserve paradigm altered by climate change
World Bank, 2012
Scarcity of water reduces photosynthetic capability and carbon uptake. Water availability tied to NPP.
Soil order and carbon sequestrationWorld Bank, 2012
Soil carbon stabilization efficacy:• Low soil organic matter (0.5-1 %)• Low microbial diversity• Low soil fertility (nutrient content
particularly N, P and S)• Widespread loss of soil functions (Poor
management)• Soil degradation and desertification• Overgrazing & excessive biomass removal
Soils with higher clay content sequester carbon at higher rates
temperate regions• 1–2% in cultivated
soils • 4–5% in grassland
and forest
Aridity and diversity and abundance of soil bacteria and fungi
Shift on microbial compositions due to aridity and loss of SOM
High occurrence of fungi facilitating microbial activity despite very low water availability (carbon
degrading enzymes).
Reduced soil fertility and climate regulation
Maestre et al. 2015
Dryland characteristics that unfavor carbon sequestration
Drier soil per se is less likely to lose carbon (Glenn et al, 1993) residence time of C is long,
sometimes even longer than in forest soils.
Soil respiration versus temperature
(volumetric water content (VWC) < 0.15) and wet (VWC > 0.35).
Sanderman et al., 2015
Soil Carbon Sequestration and TimeSoil carbon is in a constant state of flux
Dynamic nature of the soil carbon sequestration
process.
Most of the potential soil carbon sequestration takes place within the first 20 to 30 years
of adopting improved land management practices
Carbon sequestration is subject to reversibility/impermanence
While the capacity of soil carbon sequestration is potentially immense, soils can reach a carbon saturation
limit.
Maximum carrying capacity for storing soil carbon inputs
Grassland & reforestation vs carbon sequestration
Factors Affecting Soil Carbon Sequestration
Ingram and Fernandes (2001).
Due to poor management dryland ecosystems contribute 0.23 – 0.29 Gt of carbon a year to the atmosphere.
Primary production sets the upper limit on the amount of carbon
that can be stored in soil.
In Dryland, Potential Sequestration:0.4–0.6 Gt of carbon a year
(Lal, 2001)
• Erosion-induced land degradation boosts C losses in Drylands
• Despite low precipitation and microbial activity, photodegradation of above-ground biomas (carbon loss).
Austin & Vivanco, 2006
Recommended Management Practices
Recommended practices C sequestration potential(Mg C/ha/yr)
Conservation agriculture 0.10-0.40
Winter cover crop 0.05-0.20
Soil fertility management 0.05-0.10
Elimination of summer fallow 0.05-0.20
Forages based rotation 0.05-0.20
Use of improved varieties 0.05-0.10
Organic amendments 0.20-0.30
Water table management/irrigation
Lawn & Turf
0.05-0.10
0.5-1.0
Minesoil reclamation 0.5-1.0
Lal et al., 1998
Trade-offs between profitability and carbon Sequestration of sustainable land management technologies
GLOBAL POTENTIAL OF SOC SEQUESTRATION
Cropland: 0.4-1.2
Grazing land: 0.3-0.5
Salt-affected soils: 0.3-0.7
Desertified soils: 0.2-0.7
Total: 1.2-3.1
Lal (2010)
Rates of C sequestration, given in parentheses, are expressed in kg C ha-1 year-1 (from Lal, 2004).∙ ∙
(Pg C/YR)
Barriers to adoption of carbon sequestration strategies (CSS)• CSS Adoption Time barriers: Breaking down centuries of poor practices• Financial barriers (develop incentives)• Knowledge barriers (Improve knowledge management systems)• Resource barriers (tailored insurance products)• Technical and logistical barriers • Institutional barriers • Socio-cultural barriers « Carbon sequestration is a
shared responsability and the future is no longer as it used to
be »
