Challenges of soil organic carbon sequestration in drylands

Download Challenges of soil organic carbon sequestration in drylands

Post on 11-Apr-2017




0 download


Prsentation PowerPointChallenges of soil organic carbon sequestration in drylandsDr. Rachid MRABETProf. Mohamed BadraouiDr. Rachid MoussadekProf. Brahim SoudiFAO (Rome) Tuesday Mars 21st, 2017The 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. 2015Carbon mass per hectare in the drylandsUnited 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 countriesPrevent the aggravation of global desertificationSource: 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 drylandsFAO Draylands, People and Land use; Source:; 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 sequestrationWorld 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 removalSoils 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 fungiShift on microbial compositions due to aridity and loss of SOMHigh occurrence of fungi facilitating microbial activity despite very low water availability (carbon degrading enzymes).Reduced soil fertility and climate regulation Maestre et al. 2015Dryland characteristics that unfavor carbon sequestrationDrier 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 sequestrationFactors Affecting Soil Carbon SequestrationIngram 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, 2006Recommended 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/irrigationLawn & Turf0.05-0.100.5-1.0Minesoil reclamation0.5-1.0Lal et al., 1998Trade-offs between profitability and carbon Sequestration of sustainable land management technologies 15Global Potential of SOC SequestrationCropland: 0.4-1.2Grazing land: 0.3-0.5Salt-affected soils:0.3-0.7Desertified soils:0.2-0.7 Total:1.2-3.1Lal (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 LossCarbon Gain


View more >