This presentation was presented during the 1 Parallel session on Theme 3.2, Managing SOC in: Grasslands and livestock production systems, of the Global Symposium on Soil Organic Carbon that took place in Rome 21-23 March 2017. The presentation was made by Ms. Katja Klumpp, from INRA – France, in FAO Hq, Rome

1. C sequestration of a grazed permanent
grasslands: uses of complementary methods
for data analyses and interpretation
Katja Klumpp, Juliette M.G. Bloor, Rie Nemoto,
Damien Herfurth, Olivier Darsonville
GLOBAL SYMPOSIUM ON SOIL ORGANIC CARBON, Rome, Italy, 21-23 March 2017

2. Global technical mitigation potential by 2030
Drawn from data in Smith et al., 2007a.
89% of greenhouse gas savings
through C sequestration

3. 3
Distribution of EU grasslands

4. 4
• Considerable variation linked to climat, management, vegetation type
but also measure technique
Mean 0.8 (±0.16) Mg C /ha.yr
Literature : C storage in grasslands (Mg C/ha.an).

5. Literature : Equilibrium assumption of C storage in
grasslands (Mg C/ha.an).
Smith et al 2014 GBC
• 0 – 40yrs after management (land use) change
grasslands may store large amounts of C
• 100-120yrs of constant management before
Grasslands attain an equilibrium
• To improve C sequestration potential we would need better understanding of the
impacts of climat, management and vegetation.

6. • Repeated soil sampling
 Difficulty :
- large spatial heterogenity (i.e. large sampling number)
- temporal sampling intervals (5-10yrs)
- difficult to disentangle climate and management effect
• Eddy covariance gas exchange measurements
 Difficulty :
- no replicate plots
- C storage over the whole ecosystem
- link measurements to changes in soil C
Methods to measure soil organic carbon changes

7. Aims
To assess the ability to capture net carbon
sequestration of grassland ecosystems.
Method comparison
- repeated soil sampling
- eddy covariance technique
Further insight where sequestrated C goes, we analysed changes in
- spatial distribution of soil C stocks
- soil organic matter pools ( i.e. labile, passive, inert, etc)

8. Intensive (2.8ha)
1.1 LSU ha.yr-1
210 g N ha.yr-1 (3 splits)
13.7 % clover
7 dominante species (36)
Pot Prod: 7.1t DM green.ha.yr-1
Standing: 2.6t DM.ha.yr-1
Extensive (3.8ha)
0.5 LSU ha.yr-1
4.4 % clover
7 dominante species (31)
Pot Prod: 5.1 t DM green.ha.yr-1
Standing: 2.2 t DM.ha.yr-1
Set up in May 2002
Grazed May-October
Paired permanent grassland site, F-Laqueuille, Central France
Alt. 1050m, mean T 8°C, 1000mm
Flux Tower
CO2 + CH4
• Repeated soil sampling
2004, 2004, 2012
4 layers (0-10, 10-20, 20-40, 40-60cm)

9. EC technique - Net Carbon Storage
Simplified for temperate managed grasslands
NCS = FNEE - FCH4-C + Fmanure + Fharvest + Fanimal-products + Fleach
(i.e. Allard et al. 2007, Soussana et al 2010):
(NCS or N
[CO2] = C’
Vertical wind = w’
CO2 flux = w’ c’
EC-flux towers (spatial ~ 1 to 3ha )
Net Ecosystem Exchange (NEE)
X
X
X

10. O
POM DOC
O
s+c-
rSOC
S+A
Physically protected against fast
decomposition
rSOC IOM
Chemically resistant
Splitting DPM/RPM ratio
calculated by equilibrium
scenario
Splitting BIO/HUM ratio
calculated by equilibrium
scenario
Decomposable
Plant Material
(DPM)
Resistant Plant
Material
(RPM)
Microbial
Biomass (BIO)
Humified
Organic Matter
(HUM)
Inert Organic
Matter (IOM)
RothC model• Soil organic C pools -> Zimmermann et al. (2007) fractionation method
Analysed Fractions Soil C pools

11. Net C storage by EC technique
covariance
Extensive Intensive
• Mean annual
Net C storage
(Mg C/ha.yr)
1.80 (±0.5) 2.2 (±0.5)
• Cumulated (10yrs)
Net C storage (Mg C/ha) 18.9 19.9
sink
source
• Considerable variation linked to climat and management
dry dry drywet wet wet

12. – Stock changes over time (0-60cm depth, n=50 )
EXT INTEXT INTExtensif Intensif
2004
2012
C accumulates over time but no difference
between grazing treatments 12
2008
2004
2012
2008
Repeated soil sampling

13. Distribution in the soil profile
Extensive Intensive
• For equal
soil mass
SOC stock changes are mainly in deeper soil layers (>40cm)
• For observed
soil mass
gainloss gainloss
gainloss gainloss
2004-2008 (….)
2008-2012 (----)
2004-2012 (__)

14. Comparison between repeated soil sampling
and EC technique
Mg C/ha Extensive Intensive
Soil EC-flux Soil EC-flux
2004-2008 15.8 (±1.0) 8.8 14.6 (±0.8) 7.3
2008-2012 -0.8 (±1.1) 9.3 5.8 (±0.7) 11.8
2004-2012 14.9 (±1.0) 18.0 20.4 (±0.8) 19.2
Annual mean 1.9 (±0.1) 2.6 (±0.1) 1.9 (±0.1) 2.2 (±0.5)
Both methods are in good agreement for
long term comparison.

15. EXT
INT
 No spatiale dependence
due to a grazing gradient
R²=0,96
Distance
Distance
Semi-varianceSemi-variance
15
 No spatiale dependence
Where did the C go ?
Spatial distribution in the 0-10cm soil layer

16. Where did the C go ?
Mean SOC pools (Mg C/ha) over 0-60cm
Extensive Intensive
2008
2012
2008
2012
Little changes in the DPM, RPM and BIO but the HUM and IOM pool

17. Extensive
20082012
Where did the C go ?
SOC pools per layer (Mg C/ha)
HUM
IOM
Soil layers

18. Where did the C go ?
Differences in SOC pools between 2008-2012 (Mg C/ha) in the 0-60 cm
Little changes in the DPM, RPM and BIO but the HUM and IOM pool

19. Summary
• Grasslands were a sink of C
• Measured C stock changes matched well between measure methods
(2.2 Mg C/ha.yr EC technique vs 1.9 Mg C/ha.yr soil sampling)
• For bulk soil (0-60cm): only little effect was observed between grazing
treatments due to high spatial variability
• However, marked C stock changes were observed in deeper soil layer.
• This was confirmed by soil organic matter pools which showed
a transfer of C from humified C (HUM) to inert C (IOM)
- between years
- between soil layers
• EC technique allowed to disentangle climate from management effects
eg. intensive treatment had higher net C storage in dry climatic
years, vice versa for the extensive treatment.
• Methods are complementary
EC-technique offer to test effective mitigation option
repeated soil sampling; long term tendencies, baselines, land use…

20. Thank you
20