This presentation was presented during the 1 Parallel session on Theme 3.3, Managing SOC in: Dryland soils, of the Global Symposium on Soil Organic Carbon that took place in Rome 21-23 March 2017. The presentation was made by Mr. Rachid Mrabet , from INRA – Morocco, in FAO Hq, Rome

1. Challenges of soil organic carbon
sequestration in drylands
Dr. Rachid MRABET
Prof. Mohamed Badraoui
Dr. Rachid Moussadek
Prof. Brahim Soudi
FAO (Rome) Tuesday Mars 21st, 2017

2. 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)

3. 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

4. Carbon mass per hectare in the drylands
United Nations, 2011
Annual Global Primary Production
as a function of the AI (Huang et al. 2015)

5. 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

6. 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

7. 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/341043
http://www.unep.org/maweb/documents/document.291.aspx.pd
f
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.

8. Dryland characteristics that unfavor carbon
sequestration
Climate 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.

9. Soil order and carbon sequestration
World Bank, 2012
Soil carbon stabilization efficacy:
• Low soil organic matter (0.5-1 %)
• Low microbial diversity
• Low soil fertility (nutrient contenẗ 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

10. 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

11. 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

12. Soil Carbon Sequestration and Time
Soil 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

13. Grassland & reforestation vs carbon
sequestration
0
50
100
150
200
0255075100125150
Experimentduration(years)
Annual change in SOC
(g m-2 yr-1)
Reforestation
0255075100125150
Experimentduration(years)Experimentduration(years)
DatafromPostandKwon(2000)
tionofactivesoilcarbonsequestration
200C
0
5
10
15
20
25
30
35
0255075100125150
Experimentduration(years)
Annual change in SOC (%)
Grasslandmanagement
5075100125150
rimentduration(years)
andmanagement
atafromWestandPost(2002)
DatafromConantetal.(2001)
III.Durationofactiveso
0
50
100
150
200
02550
Experiment
Annual change in SOC
(g m-2 yr-1)
0
1
2
3
4
5
6
7
8
0255075100125150
Experimentduration(years)
Croplandmanagement
Annual change in SOC (%)
DatafromWestandPost(2002)
Datafro

14. 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

15. 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

16. 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)
34
Gianluca Carboni
Evaluation of conservation tillage and rotation with legumes as adaptation and mitigation strategies of climate change on
durum wheat in Sardinia
Tesi di dottorato in: Agrometeorologia ed Ecofisiologia dei Sistemi Agrari e Forestali, XXIII ciclo - Università degli Studi di Sassari
The global potential of SOC sequestration is estimated by Lal et al. (2007b), could
be comprise between 0.4 to 1.2 Gt C year-1
(Fig. 8). The total potential of sequestration is
made by 0.4 to 0.8 Gt C year-1
through adoption of RMPs in croplands (1350 Mha), 0.2 to
0.4 Gt C year-1
through restoration of degraded and desertified soils (1100 Mha), 0.01 to
0.3 Gt C year-1
through improvements of rangelands (savannas, natural grasslands,
shrublands etc.) and grasslands (3700 Mha) and 0.01 to 0.03 Gt C year-1
on irrigated soils
(275 Mha) (Lal et al., 2007b).
Fig. 8 –Potential of Carbon sequestration. Rates of C sequestration, given in parentheses, are expressed in kg
C∙ha-1
∙year-1
(from Lal, 2004).
Reductions in SOC, as well as cause CO2 emissions, involve damage to the
potential productivities of soils. Indeed it has been evaluated that a loss of 1 t ha-1
of SOC
Rates of C sequestration, given in parentheses, are expressed in
kg C∙ha-1∙ year-1 (from Lal, 2004).
(Pg C/YR)

17. 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 »

18. Thank you
rachidmrabet@gmail.com
http://www.inra.org.ma
Carbon Loss Carbon Gain