This presentation was presented during the 2 Parallel session on Theme 2, Maintaining and/or increasing SOC stocks for climate change mitigation and adaptation and Land Degradation Neutrality, of the Global Symposium on Soil Organic Carbon that took place in Rome 21-23 March 2017. The presentation was made by Ms. Claire Chenu, from INRA - France, in FAO Hq, Rome

1. Agricultural practices that store organic
carbon in soils: is it only a matter of inputs ?
Claire Chenu1, Rémi Cardinael1,2, Bénédicte
Autret3, Tiphaine Chevallier2, Hélène Guiller1,3,
Thomas Cozzi1, Cyril Girardin1, Bruno Mary3
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GSOC 2017-Chenu et al.
1 AgroParisTech-INRA, Ecosys, Grignon, France
2 IRD, Eco&Sols, Montpellier, France
3 INRA, AgroImpact, Laon, France
claire.chenu@inra.fr

2. How to increase soil C in agricultural soils ?
2
Primary production
1
4
Plant respiration
exports
restitutions
2
imports
3
Inputs
leaching
erosion
Biodegradation
& mineralisation
5
6
GSOC 2017-Chenu et al.
Available levers :
Need to change cropping systems towards less inputs and less
negative environmental impacts

3. Aims of this study
• Assess the effects of agroecological practices
on soil C stocks (temperate conditions)
– Low input
– Organic farming
– Conservation Agriculture
– Agroforestry
• Identify levers
– Increase C inputs,
– Decrease C outputs
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3
Long term experiments
Organic C stocks
measurements
OC inputs measurements
OC mineralization measurements

4. 1- Sites and measurements
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5. Alternative cropping systems: experiment
• Long term trial of La Cage, Versailles 16y
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Average 1998-2014 Conventional
CON
Low Input LI Conservation
agriculture CA
Organic ORG
Tillage Each year 1 year/2 No till Each year
Mineral fertilisers +++ ++ ++ 0
N fertilization (kg ha-1 yr-1) 143 114 104 10
Pesticides +++ + ++ 0
Permanent plant cover no no yes (fescue,
alfalfa)
no
Wheat yield (t ha-1 yr-1) 9.7 8.9 6.7 5.4
Block 1Block 2
ORG
16.1
ORG
16.2
CA
17.1
CA
17.2
CON
18.1
CON
18.2
LI
19.2
LI
19.1
ORG
13.1
ORG
13.2
CA
12.1
CA
12.2
CON
15.1
CON
15.2
LI
14.2
LI
14.1
• Wheat, pea, rapeseed, maize, alfalfa
• Luvisol

6. Silvoarable agroforestry: experiment
• Long term trial of Restinclières 18y
– Carbonated Fluvisol
– Alley cropping, walnut trees intercropped with durum wheat
– 110 trees ha-1
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R. Cardinael
R. Cardinael
Control plot
Agroforestry plot

7. Methods
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• Soil C stocks
• OC inputs
• OC outputs
• Depth 0.6m / 2m
• C contents & bulk density
• Equivalent soil mass
• Measured : yields
• Estimated : Versailles AG and BG biomass
• Measured :
• OC mineralization in incubation
Litter
Tree row
vegetation
Tree root biomass
& turnover
Photos©R.Cardinael
©Guiller
Photos©R.Cardinael

8. 2- Results
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9. Alternative cropping systems: results
• C stocks
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0
10
20
30
40
50
60
70
CON LI CA ORG
SOCstocks(tCha-1)
1998
2014
a
a a
a
A
A
A
B
 Increased C stocks in conservation agriculture system
(0-30 cm: + 0.55 t C ha-1 yr-1)
Autret et al. 2016, Agric Ec Env
0-30 cm

10. Alternative cropping systems: results
• Organic inputs to soil
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 Increased C inputs in
conservation agriculture
system (+ 32%)
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100 120
mineralizedC(%soilC)
me (days)
CA
ORG
LI
CON
 no difference
• OC mineralization
Autret et al. 2016, AEE Guiller 2016, MS report

11. Silvoarable agroforestry: results
AGROFORESTRY
30
50
100
0
Depth(cm)
REFERENCE
200
Cardinael et al. 2015, GeodermaGSOC 2017-Chenu et al.
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95.6 ±0.893.5 ±0.5
35.8 ±0.2 40.3 ±0.5 + 0.25 (t C ha-1 y-1)
Increased C
stocks

12. Silvoarable agroforestry: results
AGROFORESTRY
30
50
100
0
Depth(cm)
REFERENCE
200
Cardinael et al. submGSOC 2017-Chenu et al.
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Δ fresh C inputs to soil (tC ha-1 y-1) + 40%
row vegetation
(+ 0.34)
tree litter (+0.73)
crop residues (-0.17)
row vegetation
roots (+ 0.10)
row vegetation
roots (+ 0.02)
crop roots (-0.57)
crop roots (-0.46)
crop roots (-0.09)
tree roots (+0.52)
tree roots (+0.35)
tree roots (+0.34)
0
0,5
1
1,5
2
2,5
3
3,5
0-10 cm 10-30 cm
mineralizedSOC44d(%SOC)
depth
Control
AF inter row
AF tree row
Mineralization in incubation
+ in tree rows
Cozzi, 2015, MS report

13. 3- Discussion and conclusion
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14. Soil C storage in alternative cropping systems
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Increased C
inputs to soil
Increased soil C stocks
No decrease in C
mineralization rate
2- Modelling : SOC stocks evolution are well reproduced with the
same decomposition constant for all cropping systems
Versailles : Autret et al. 2016 AEE
Agroforestry Restinclières : Cardinael et al. submitted AMG model, Saffih-Hdadi & Mary, 2008
1- Field experiments :

15. Soil C storage in alternative cropping systems
EGU 2016-04-20 Chenu et al.
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• Expert assesment by
Pellerin et al. 2013. How can
French agriculture contribute to
reducing greenhouse gas emissions?
Abatement potential and cost of ten
technical measures
3- Litterature:
Angers & Eriksen Hamel 2008; Luo et al. 2010,
AEE; Virto et al. 2012, Biogeochemistry
• Meta-analyses: no till compared to full inversion tillage
Practices that increase inputs to soil are the ones which
have the best potential to store C
Nul or limited effect of no-tillage; high variability

16. Conclusion
• Cropping systems/ practices that increase C inputs
to soil increase SOC stocks
• Increasing inputs seems « more efficient » than
reducing outputs
• Need to explain the variability of tillage effects on
SOC stocks
• Other processes ? (microbial community structure,
metabolism, priming effects…)
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17. Thank you for your
attention
claire.chenu@inra.fr
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