challenges of soil organic carbon sequestration in drylands

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Challenges of soil organic carbon sequestration in drylandsDr. Rachid MRABETProf. Mohamed BadraouiDr. Rachid MoussadekProf. Brahim Soudi

FAO (Rome) Tuesday Mars 21st, 2017

The largest biome on Earth 41.3 % of the Earths continental area (430 Millions ha) and is expanding.38% of the worlds 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 drylandsNo 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); 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;


Supporting 50% of the worlds 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 30C) Cold temperatures (mean annual temperature less than 20C).Pulse-reserve paradigm altered by climate change

World Bank, 2012Scarcity of water reduces photosynthetic capability and carbon uptake. Water availability tied to NPP.

Soil order and carbon sequestration

World Bank, 2012Soil carbon stabilization efficacy:Low soil organic matter (0.5-1 %)Low microbial diversityLow soil fertility (nutrient content particularly N, P and S)Widespread loss of soil functions (Poor management)Soil degradation and desertificationOvergrazing & excessive biomass removal

Soils with higher clay content sequester carbon at higher rates temperate regions12% in cultivated soils 45% 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:0.40.6 Gt of carbon a year (Lal, 2001) Erosion-induced land degradation boosts C losses in DrylandsDespite low precipitation and microbial activity, photodegradation of above-ground biomas (carbon loss).Austin & Vivanco, 2006

Recommended Management PracticesRecommended practicesC sequestration potential(Mg C/ha/yr)Conservation agriculture0.10-0.40Winter cover crop0.05-0.20Soil fertility management0.05-0.10Elimination of summer fallow0.05-0.20Forages based rotation0.05-0.20Use of improved varieties0.05-0.10Organic amendments0.20-0.30Water table management/irrigation

Lawn & Turf0.05-0.10

0.5-1.0Minesoil reclamation0.5-1.0

Lal et al., 1998

Trade-offs between profitability and carbon Sequestration of sustainable land management technologies


Global Potential of SOC SequestrationCropland: 0.4-1.2

Grazing land: 0.3-0.5

Salt-affected soils:0.3-0.7Desertified soils:0.2-0.7 Total:1.2-3.1

Lal (2010)

Rates of C sequestration, given in parentheses, are expressed in kg Cha-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 practicesFinancial 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

Thank yourachidmrabet@gmail.com

Carbon Loss

Carbon Gain


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