agricultural practices that store organic carbon in soils: is it only a matter of inputs ?
TRANSCRIPT
GSOC 2017-Chenu et al.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
1 AgroParisTech-INRA, Ecosys, Grignon, France2 IRD, Eco&Sols, Montpellier, France3 INRA, AgroImpact, Laon, France
GSOC 2017-Chenu et al.2
How to increase soil C in agricultural soils ?
Primary production1
fire4
Plant respirationexports
restitutions
2
imports
3
Inputs
leaching
erosion
Biodegradation& mineralisation
5
6
Available levers :
Need to change cropping systems towards less inputs and less negative environmental impacts
GSOC 2017-Chenu et al.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
Long term experiments
Organic C stocks measurements
OC inputs measurements
OC mineralization measurements
GSOC 2017-Chenu et al.4
1- Sites and measurements
GSOC 2017-Chenu et al.5
Alternative cropping systems: experiment• Long term trial of La Cage, Versailles 16y
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
• Wheat, pea, rapeseed, maize, alfalfa• Luvisol
GSOC 2017-Chenu et al.6
Silvoarable agroforestry: experiment• Long term trial of Restinclières 18y
– Carbonated Fluvisol– Alley cropping, walnut trees intercropped with durum wheat – 110 trees ha-1
R. Cardinael
R. Cardinael
Control plot
Agroforestry plot
GSOC 2017-Chenu et al.7
Methods• 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
LitterTree row vegetation
Tree root biomass & turnover P
hoto
s ©
R.C
ardi
nael
©G
uille
r
Pho
tos
©R
.Car
dina
el
GSOC 2017-Chenu et al.8
2- Results
GSOC 2017-Chenu et al.9
Alternative cropping systems: results• C stocks
CON LI CA ORG0
10
20
30
40
50
60
1998
2014
SOC
sto
cks
(t C
ha-
1)a
a aa
AA
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
GSOC 2017-Chenu et al.10
Alternative cropping systems: results
• Organic inputs to soil
Increased C inputs in conservation agriculture system (+ 32%)
no difference
• OC mineralization
Autret et al. 2016, AEE Guiller 2016, MS report
Silvoarable agroforestry: results
AGROFORESTRY
30
50
100
0
Dep
th(c
m)
REFERENCE
200
Cardinael et al. 2015, GeodermaGSOC 2017-Chenu et al. 11
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
Silvoarable agroforestry: results
AGROFORESTRY
30
50
100
0
Dep
th(c
m)
REFERENCE
200
Cardinael et al. submGSOC 2017-Chenu et al. 12
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)
Mineralization in incubation+ in tree rows
Cozzi, 2015, MS report
GSOC 2017-Chenu et al.13
3- Discussion and conclusion
GSOC 2017-Chenu et al.14
Soil C storage in alternative cropping systems
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 AEEAgroforestry Restinclières : Cardinael et al. submitted
AMG model, Saffih-Hdadi & Mary, 2008
1- Field experiments :
EGU 2016-04-20 Chenu et al.15
Soil C storage in alternative cropping systems
• 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
GSOC 2017-Chenu et al.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…)
