Temperature (°
a)
TA
Carbon balance of an intensive grazed grassland
20
TS
10
0
-10
2. EXPERIMENTAL SITE
•Situation: Belgium, Dorinne (l50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 m asl.)
PPFD (µmol m-2 s-1)
•Climate: temperate oceanic
•Mean annual temperature: 10°C
•Annual precipitation: 800 mm
•Type: permanent grassland
•Surface: 4.2 ha
10
0
-10
4
3-Jun - 6-Jun-10
Cut-harvest
2.7
10-Jun-10
Fertilisation: 24/0/0 + Se
0.2
Amount (t ha )
12-Jun - 11-Jul-10 Complementary feedings
0.9
31-Jul - 21-Aug-10 Complementary feedings
1.0
1
Belgian Blue heifers: 400 to 500 kg
Feb11
Apr11
Belgian Blue suckler cows: 760 kg
Fig. 1: Instantaneous stocking rate (livestock unit per
hectare, LU ha-1) between 12 May 2010 and 12 May
2011).
0.6
12
b)
10
0.4
8
6
0.2
4
2
0
0
0.6
12
0.2
4
2
0
0
800
c)
600
400
200
0
Jun10
Aug10
Oct10
Dec11
Feb11
Apr11
3.5
20-Feb-11
Fertilisation: compost (t ha -1 )
12.0
9-Mar-11
Fertilisation: 18/5/5 + Mg (t ha -1 )
0.4
22-Mar-11
Liming: CaO (t ha-1 )
1.5
•Rotational grazing: mean annual stocking rate = 1.6 LU
•Intensive management
ha-1
4. CARBON BUDGET ESTABLISHMENT
b)
10
Summer 2010 (June – early
August):
•High temperatures
•Very few precipitations

c) Limited soil moisture
content
0.4
8
6
0.2
4
2
0
0
c)
600
400
200
0
Jun10
800
600
400
200
0
Jun10
Aug10
Oct10
Dec11
Feb11
Apr11
Aug10
Spring 2011 (March – early May):
•Exceptionally sunny conditions
•Minimal and maximal daily temperature
higher or equal to normal
•Very little precipitation: <60 mm (200
mm in normal)
 Limited soil moisture content at the
beginning of May
Oct10
Dec11
Feb11
Apr11
12
No cattle
Cattle
30
20
10
NBP=NEE+CNBP,import+CNBP,complement+CNBP,export+CNBP,CH4+CNBP,lw+CNBP,leach
Table 2: Measurement methods of carbon fluxes.
NBP
Method of estimation
NEE
Direct measurement: eddy covariance and micrometeorology
CNBP,import
(DM estimate by the farmer) × C content
CNBP,complement
(difference between herbage mass before and after the harvest) × C content
CNBP,export
CNBP,CH4
CNBP,lw
Estimation based on dry matter intake (DMI): Lassey, 2007
Deduced from budget: Cintake + CNBP,complement - Rl - Cexcretions - CNBP,CH4
CNBP,leach
Other C fluxes
NPP
Cintake
Estimation based on Schultze et al. (2009): 7±7 g C m-2 y-1
Rl
Soussana et al. (2007): 40-75% of C intake
Cexctretions
Soussana et al. (2007): 25-40% of C intake
For a determined period: (DMafter - DMbefore) × C content
Macoon et al. (2003): for a determined period: (DMbefore - DMafter) × C content
No cattle
Cut
Cattle
5.3 Seasonal course of the fluxes
•Spring 2010:
20
a)
High accumulation of C in the system: fluxes dominated by
photosynthesis
GPP reached its maximal value by the end of May
10
0
TER
-10
•Cutting:
GPP
-20
GPP decreased due to the removal of photosynthetic material 
abrupt decline of NEE
10
0
1 2 3 4 5 6 7 8 9 10 11 12 13
8
•Variations between periods due
to climate and management (cut,
consecutive re-growth, drought).
•Effect of drought: limited values
(≈ 18 µmol m-2 s-1.) during
periods 4-6 and 12-13
Dry conditions precluded C accumulation.
GPP declined more than TER as the soil dried out  source of CO2
in mid July
0
-5
•Mid August - end of September:
-10
Better climatic conditions  CO2 neutral (Figure 3c).
•From October:
300
Lower temperatures and radiation  assimilation decreased and net
fluxes dominated by TER
End of November:
GPP ≈ 0, TER declined to low levels and NEE >0  end of January
c)
150
0
-150
Jun10
Aug10
Oct10
Dec11
Feb11
Apr11
•Since the end of January:
TER and GPP gradually increased  start of March: CO2 sink
 Cumulative NEE = 172 ±53 g C
the site behaved as a net CO2 source
-2
m
-1
y
1 2 3 4 5 6 7 8 9 10 11 12 13
-2 -1
•Similar (but much lower) variations between
periods compared to Amax.
•Very high (up to 10 µmol m-2 s-1) values.
20
No Cattle
Cattle
Lloyd and Taylor fit
Bin average
Flux (g C m y
GPP
-2268
TER
2440
NEE
172
CNBP,import
-91
CNBP,comple me nt
-103
CNBP,e xport
38
CNBP,CH4
12
CNBP,lw
23
CNBP,le ach
7
)
±
±
±
±
±
±
±
53
9
3
4
1
18
7
NBP
NPP
Cintake
Rl
Ce xcre tions
±
±
±
±
±
58
14
16
57
306
247
201
114
7
4
•Annual GPP and TER considerably larger than any
other fluxes
-2
-1
•Annual C inputs (≠ GPP) =194 g C m y ≈ NEE
•Annual C export ≈ 25% of C inputs
Balance between C imports and C exports created
a large departure of NBP from NEE: Cumulative
NBP = 57 ±58 g C m-2 y-1
•Considering uncertainties: NPP = Cintake + CNBP,export
•Cattle respiration (Rl) is lower than 10 % of TER
10
The site behaved as a small source of carbon, BUT:
5
0
0

Table 3: annual carbon fluxes at Dorinne
grassland site (12 May 2010 -12 May 2011).
Rd evolution
15
5
5.4 Carbon balance and related fluxes
4
0
•Most intensive growth during
period 1: Amax = 33 µmol m-2 s-1.
b)
6
Fig. 4: Evolution of assimilation at light saturation and daytime respiration for different periods of the study years. Values are
deduced from daytime flux/radiation response. Error bars represent 95% confidence intervals.
Amax evolution
•Start of July:
10
Fig. 6: (a) Daily totals of Total Ecosystem Respiration
(TER), Gross Primary Productivity (GPP), (b) Net
Ecosystem CO2 Exchange (NEE) and (c) cumulative
NEE. Fluxes are presented over one year of
measurements (12 May 2010 – 12 May 2011).
2
Nighttime flux
•High respiration values
•No short term response of
nighttime respiration to
temperature
•No clear livestock impact on
respiration flux
Fig. 2: Carbon balance of a grazed grassland.
Rainfall (mm)
6
800
Rd (µmol m-2 s-1)
Type
Dec11
-10
Nighttime flux (µmol m-2 s-1)
Date
7-Sep - 22-Nov-10 Complementary feedings
Unit of Biosystem Physics
Fig. 3: Daily means of air temperature (TA) and soil temperature at 2 cm depth (TS), (b) Soil moisture at 5 cm depth and rainfall and
c) Daily means of Photosynthetically Photon Flux Density (PPFD) meaasured at Dorinne (12 May 2010 – 12 May 2011).
Amax (µmol m-2 s-1)
Instantaneous stocking rate (LU ha-1)
-1
5
Oct10
0
40
Table 1: List of management activities from 12 May 2010 to
12 May 2011.
Aug10
10
C fluxe (g C m -2 day -1)
TS
3. GRASSLAND MANAGEMENT
Jun10
8
5.2 Impact of climate and management on CO2 flux
•Slope: moderate (1 to 2 %)
0
TA
20
Soil moisture (m -3 m -3)
This poster:
•To analyze the yearly carbon budget of the grassland
2
0.4
NEE (g C m-2 day -1)
•To propose mitigation scenarios in order to improve the GHG balance
3
12
Cumulative NEE (g C m -2)
Temperature (°C)
•To compute carbon and GHG balances of a grazed managed grassland
a)
TS
PPFD (µmol m-2 s-1)
30
20
Rainfall (mm)
5.1 Climate
Temperature (°C)
Long term objectives:
Soil moisture (m -3 m -3)
1. OBJECTIVES
5. RESULTS
6
0.6
30
University of Liege, Gembloux Agro-Bio Tech, Unit of Biosystem Physics, 8 Avenue de la Faculté,
B-5030 Gembloux, Belgium - 2 University of Liege, Gembloux Agro-Bio Tech, Animal Science Unit, 2 Passage des Déportés, B-5030 Gembloux, Belgium 10
b) B-5030 Gembloux, Belgium.
3 University of Liege, Gembloux
a) Agro-Bio Tech, Crops Science Unit, 2
TAPassage des Déportés,
Rainfall (mm)
PPFD (µmol m-2 s-1)
1
Soil moisture (m -3 m -3)
Jérôme Elisabeth1, Beckers Yves2, Bodson Bernard3, Moureaux Christine3, Aubinet Marc1
5
10
15
20
Soil temperature at 2 cm depth (°C)
25
Fig. 5: Dependence of nighttime respiration on soil temperature:
overall fit (12 May 2010 – 12 May 2011). Data are filtered for u* and
stationarity.
 No significant difference between periods with and without cattle
• The NBP value is not significantly different from zero
• NEE < 10% (TER and GPP)  a small relative change in one of these
fluxes may strongly modify the net budget
• It was obtained under particular climatic conditions, characterised by
drought during summer 2010 and spring 2011
6. CONCLUSIONS
7. PERSPECTIVES
•High respiration value < > low assimilation value
 The site behaved as a net source of CO2
•The NBP is not significantly different from zero
 To conclude about the sink or source activity of the plot,
long term measurements are necessary
•Second year of measurements: comparison between the C budget
 Impact of climate on the C budget?
•To analyze the drought impact in summer 2010 and spring 2011
 H2O fluxes
•Measurements of N2O and CH4  full GHG budget
This research was funded by The « Direction Generale opérationnelle de l’Agriculture, des Ressources naturelles et de l’Environnement - Région Wallonne » Project n° D31-1235, January 2010 - December 2011
Contact Person: Jérôme Elisabeth - University of Liege – Gembloux Agro-Bio Tech (GxABT) - Unit of Biosystem Physics, 8 Avenue de la Faculté - 5030 Gembloux - Belgium
Tel : +32 (0)81 62 24 90 - Fax : +32 (0)81 62 24 39 e-mail : [email protected]