The role of grassland in mitigating climate change, an EU perspective Sustainable Agriculture Initiative (SAI)

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The role of grassland in mitigating climate change, an EU perspective Sustainable Agriculture Initiative (SAI)

Katja Klumpp

To cite this version:

Katja Klumpp. The role of grassland in mitigating climate change, an EU perspective Sustainable Agriculture Initiative (SAI). Carbon sequestration in grasslands workshop, Dec 2014, Bruxelles, Bel- gium. �hal-02801749�

The role of grassland in mitigating climate change – An EU perspective

Katja Klumpp

Grassland Ecosystem Research Unite, Clermont Ferrand, France katja.klumpp@clermont.inra.fr

SAI Sustainable Agriculture Initiative (SAI) Platform

- Carbon sequestration in grasslands workshop,Brussels, Belgium, 4^th December 2014

Outline

Soil C stock vs C storage (sequestration) The European grassland carbon sink

Why is grassland management critical?

3

4

-40 -20 0 20 40 60 80 100

Grassland Cropland

Forest CH4 agriculture N2O

Mt C y^r-1

GHG balance of the agriculture sector in EU25

- Grassland C sequestration would play a significant role for the European agriculture sector - for France an increase in soil C stocks by 0.2 % per year (6 Mt) may compensate 4% of french GHG emissions

(After Schulze et al., 2009 Nature Geoscience)

5

Photosynthesis (CO₂ assimilation)

Carbon Storage

Rhizodeposition

Organic Fertiliser (Manure)

C storage ≠ soil C stock

+

+

+

+

Animal dejections

+ -

Soil respiration

-

Ecosystem respiration

Gain growth

Carbon storage (sequestration) is an active process and which takes into account all inputs and

outputs of carbon

+

litter

Animal Respiration

Ingestion CH₄

-

6

Soil organic C stocks in Europe (% C organic)

Soil C stock is a result of a long term C storage,

- Climate, - Soil texture - Vegetation type - Human activity-

Kätterer et al 2012

Soil C storage = C stock changes over time

80 years

0.12

0.45

0.3

1.6

0.65

1.04

0.54

-0.81 0.56

0.28 1.7

2.53

0.9

1 1.6

2.55

0.37

-2 -1 0 1 2 3 4 5

Stockage C (Mg C/ha.yr)

Literature : C storage in grasslands (Mg C/ha.an).

•

Considerable variation linked to climat, management and vegetation type Mean 0.9 (±0.25) Mg C /ha.yr

Sink C

Source C

Aims

Synthesize existing data on climate, management, C fluxes and C stocks of EU Grasslands

• Analyse carbon sink potential

• Drivers of soil C sequestration

- separate management and climatic effects

• Role of non CO

emissions

29 grassland flux tower sites (since 2002; 173 site-yrs) 19 permanent grasslands (>5yrs and natural) 8 temporary sown grasslands

2 Savannah

•along a climatic gradient

MAT (2°C to 15C°) , MAP (260mm to 1349mm), SOC (~4 to 72 kg C/m2)

•along agricultural gradient

- high and low N input (0 to 320 kgN/ha.yr mineral and organic) - mowing (C; 1 to 5 cuts),

- grazing (G; 0.2 to 2 LSU/ha.yr), mixed (G/C).

EU-Grasslands

Synthesis existing and emerging data

11

Eddy covariance flux towers - Net Ecosystem Exchange (NEE)

[CO₂] = C’

Vertical wind = w’ CO₂flux = w’ c’

EC-flux towers (spatial ~ 1 to 3ha ) Net Ecosystem Exchange (NEE)

Definition of Net Carbon Storage (NCS)

Simplified for temperate managed grasslands

NCS = (F

+ F

) - F

- F

- F

- F

(i.e. Allard et al. 2007, Soussana et al 2010):

[CO₂] = C’

Vertical wind = w’ CO₂flux = w’ c’

EC-flux towers (spatial ~ 1 to 3ha ) Net Ecosystem Exchange (NEE)

X

X X

inputs outputs

-600 -500 -400 -300 -200 -100 0 100 200

6 8 10 1412 1816

2000 600400

1000800 14001200

18001600 NEE (g C m

-2 yr-1 )

Temperature (°C)

Precipitation (mm) G

G / C

G

C G

/

C C/G G / C

C G

G /

C C/G

G

G G

C G

G

G / C

G

G G

G G / C C

C

C

G

C C

C C

C

G

C G

C

G

C

C G G

CG

G

CG G

G

G

G / C C

C C

C

G G

C C

G CC

G G

G

C C/G G

G C/G

G C C

G G

G

C

G / C

G

G / C C

G G C

C

C G G G

C C

C C

G

G G

G C

C

C

G

G C

G G

G G C

G / C

C G

C C

G C/G C

C C

G C

C G C G C C

Source C

Sink C

• NEE depends on annual precipitation and temperature Net ecosystem exchange (NEE)

C - cut G - grazed

14

NCS mean = 71 ± 13 g C m ^-2 yr ^-1 (P <0.001) 95% range of the NCS median: 38 to 81 g C m^-2 yr^-1

Frequency distribution of annual net carbon storage (NCS, g C m

yr

)

NCS = (F_CO2 + F_manure) - F_CH4-C - F_harvest - Fanimal-products - F_leach

C Sink activity - Net carbon Storage

Net Carbon storage (NCS, g C m^-2 yr^-1)

-600 -400 -200 0 200 400 600

Grazing Mowing All

Agricultural practices

sink source

71 (81)±13

67 (66)±19

103 (144)±20

n=163

n=66

n=144

Net Carbon storage (NCS, g C m^-2 yr^-1)

-600 -400 -200 0 200 400 600 800

Permanent

&Natural Temporary

&Sown

Wet All

Grassland type

n=163

n=129

n=43

n=20

71 (81)±13

74 (96)±13

72 (59)±34 15(43)±16

sink source

median (mean)±SE

There was no significant effect of grassland type and of management by cutting or grazing on NCS.

Net C storage and fertilisation

Sown Permanente Mown Grazed Sink C

Source C

•

A moderate fertilisation increases C storage.

all

17

•

A moderate fertilisation increases can maintain C storage and compensate for non CO2 emissions.

Net GHG Balance and fertilisation

-750 -550 -350 -150 50 250 450

0 100 200 300 400

NCS (gC/m2 .yr)

Herbage use (g C/m².yr)

Grazing Mowing zero Fertilisation

Net C storage and herbage use

Sink C Source C

• Carbon sequestration occurs frequently, even in intensive pastures

• extensive mowing/zero N-fertilisation seems to maintain C sequestration

-750 -550 -350 -150 50 250 450

0 100 200 300 400

NCS (gC/m2 .yr)

Herbage use (g C/m².yr)

Mowing+Fertilisation Grazing Mowing zero Fertilisation

Net C storage and herbage use

• Carbon sequestration occurs frequently, even in intensive pastures

• extensive mowing/zero N-fertilisation seems to maintain C sequestration

• Intensive mowing/fertilisation -> source of C

Sink C Source C

critical stocking rate

If carbon storage increases with herbage use, can we estimate a

“critical herbage use” leading to zero carbon storage?

20

If carbon storage increases with herbage use, can we estimate a

“critical herbage use” leading to zero carbon storage?

-400 -300 -200 -100 0 100 200 300 400

0.0 0.1 0.2 0.3 0.4 0.5 0.6

NCS (g C/m2.yr)

Herbage use/photosythesis

Critical herbage use leading to zero carbon storage

Grazing Mowing

Critical herbage use efficiency* = 0.20 SR* max = 2.1 LSU/ha

Net GHG Budget (CO

eq)

Net GHG Budget (g CO2eq m^-2 yr^-1)

-2000 -1000 0 1000 2000

Grazing Mowing All

40 (12)±48

100 (143)±69

35 (18)±75

n=163

n=66

n=144

Agricultural practices

sink source

Net GHG Budget (g CO2eq m^-2 yr^-1)

-1400 -700 0 700 1400

Permanent

&Natural Temporary

&Sown All

n=163

n=129

n=43 -96 (-280)±132

51 (118)±42 40 (12)±48

Grassland types

sink source

median (mean) ±SE

Does C sequestration compensate for non CO

emissions (CH

, N

O) on-site?

Relation between intensification herbage use C storage and GHG emissions

Soussana &Lemaire 2014

grazing mowing

Conclusion - comments

1. The carbon sink of European grasslands results from past/current changes in management (grassland fertilization, reduction in stocking density) and from global change (rise in atmospheric CO2 and warming).

2. Grasslands are a sink of C 0.7±0.13 Mg C/ha.yr.

3. This carbon sink can be managed by grazing and by fertilization. A better understanding of the role of these drivers and of their interactions with soil and vegetation types may allow designing guidelines for carbon neutral pastures.

4. Such carbon neutral pastures are often extensive. However, an

extensification is currently not economically possible (solution: carbon

markets, agricultural subsidies).

Thank you!