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Drainage of Flooded Rice Soil Influence the Residue
Carbon Contribution in Methane Emissions
Climate Food and Farming Network (CLIFF) Workshop 2017
7-11 November, 2017
Azeem Tariq1,2, Lars Stoumann Jensen1, Bjoern Ole Sander3, Stephane de Tourdonnet2, Per Lennart
Ambus4,Phan Hữu Thành5,Trinh Van Mai5 and Andreas de Neergaard1
1 Department of Plant and Environmental Sciences, University of Copenhagen, Denmark
2 Montpellier SupAgro-IRC, UMR 951 Innovation SupAgro-INRA-CIRAD, Montpellier, France
3 International Rice Research Institute (IRRI),Los Banos, Philippines
4 Center for Permafrost, Department of Geosciences and Natural Resource Management,University of
Copenhagen, Øster Voldgade 10, 1350 København K, Denmark
5 Institute for Agricultural Environment, Vietnamese Academy of Agriculture Sciences, Hanoi, Vietnam

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1. Introduction
ü Information on the contribution of added organic residue carbon in CH4 and CO2
emissions is essential for understanding their C dynamics with changing water
management in paddy soil.
ü There is little experimental evidence showing the direct relationship between soil
aeration and changes in residue C contribution in CH4 and CO2 emissions.
ü The present study was conducted in the laboratory with 13C-enriched rice straw as a
tracer to monitor the effect of different drainage patterns on residue C contribution in
CH4 and CO2 emissions, and to find GHG mitigation potential of drainage practices
based on reduced global warming potential (GWP).
Key words: straw carbon, early drainage, methane mitigation

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2. Materials and methods
Soil collection and pot preparation
§ The soil used in the experiment was collected from
northern Vietnam
§ The soil was sieved (<2 mm) to remove coarse
material prior to use
§ The pots with inner diameter 14 cm and height 30 cm
were filled with dried soil (3 kg per pot)
§ Rice residue was thoroughly mixed with soil prior to
packing (applied at the rate of 3.44 g kg-1 dry soil)

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Experimental set-up
The experiment was carried out in a
controlled environment growth chamber
The pots were divided into two groups, 36 pots
with rice plantation and 6 pots without rice
plantation
§ Six water treatments with rice residues and
unlabeled rice plants
§ Three water treatments (C, M and EM) and
13C plant labeled. With rice residues and
without rice residues, respectively
§ Each water treatment was replicated three
times in planted pots
§ While in unplanted pots, each water
treatment has one replicate

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Water management
Six water treatments
§ continuous flooding [C],
§ early-season drainage [E],
§ midseason drainage [M],
§ pre-season drainage [P],
§ early-season + midseason drainage [EM],
§ pre-season + midseason drainage [PM],
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$DAT$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$60$$
DAT$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$14$$$$$$$$$21$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$60$$
$$
$DAT$$$+7$$$$$$$$$+1$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$40$$$$$$$$45$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$60$$
$$DAT$$$+7$$$$$$$$+1$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$60$$
C E M P EM PM
DAT

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Rice plant labeling
§ The rice plants were pulse labeled with 13CO2 by
acidification of Na213CO3 solution with 2M H2SO4
§ The chamber will kept close for 4 hours and rice
plants will allow to photosynthesized in 13CO2 enrich
environment.
Fertilizeruses
All treatments received the same amount of mineral
(NPK) fertilizers
• Nitrogen 0.38 g N per pot
• super phosphate 0.15 g P per pot
• Potassium 0.22 g K per pot

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Gas sampling
§ Total 16 gas samples were collected over the 58 days of
experimental period
§ Gas samples were taken using a 10-ml syringe equipped
with a needle
§ three gas samples were collected at 20-minute intervals
(at time 0 and after 20, 40 min.)
§ the gas samples were injected into an evacuated 3 ml
vial
§ samples were collected in an evacuated 12 ml vial at 40
min for 13CH4 and 13CO2 analysis

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Calculation
§ The isotopic signature of the emitted CH4 and CO2 was calculated by using
following equation (Krüger et al., 2001):
S = [(B × b) - (A × a)] / (B - A)
§ The contribution of 13C-enriched rice residue to the total CH4 or CO2 emissions
were quantify following the 13C-enriched method explained by Conrad et al.
(2012):
F = (δ13Cstraw, CH4/CO2 – δ13CSOM+plant, CH4/CO2) / (δ13Cstraw – δ13CSOM+plant, CH4/CO2)

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3. Results
Methane fluxes and δ13C of emitted
methane
§ The highest fluxes were observed in
the C compared to other treatments
§ The P and PM treatments resulted in
lowest CH4 fluxes in the early stage
which remained lower throughout
the experimental period.
§ The δ13C-CH4 in P and PM
treatments decreased significantly
at 1 DAT, and then remained low
compared to other treatments
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100
150
200
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5
10
15
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C P E M PM EM
CH4fluxes-(μgg11soil-day11)
M
EM
C
0
1
2
3
4
5
Days-after-transplanting
P
E
PM
δ13CH4(‰)

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Total and straw derived CH4
0
50
100
150
200
250
300
350
400
C P E M PM EM
Cumulative-CH4emissions
(µg-CH4g61
soil)
Total
Straw/derived
a4
ab
abc
bc
c
c
a4
ab
bc bc
c
bc
Cumulative CH4 emissions (µg CH4 g-1
soil) and proportion of straw
derived CH4 emissions (µg CH4 g-1
soil) with different water regimes;
continuous flooding [C], pre-season drainage [P], early-season
drainage [E], midseason drainage [M], pre- season plus midseason
drainage [PM], and early-season plus midseason drainage [EM].
Values represent the mean of three replicates ± standard error (SE).
The lower-case letters indicate a significant difference (p<0.05)
between water regimes
§ The total CH4 emissions decreased
in the order, C > M > E > EM > P >
PM
§ The straw derived CH4 emissions
followed the same trends between
treatments as total CH4 emissions

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Plant biomass and GWP
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Water regimes
Aboveground
biomass (g pot-1)
Straw contribution
in CH4-C emission
(%)
GWP (CH4+N2O)
(mg CO2-eq g-1 soil)
N2O
contribution in
total GWP (%)
Continuous flooding [C] 4.0 (±1.2) 61.2 (±5.9) 12.1 (±2.9) 19 (±9)
Pre-season drainage [P] 6.6 (±2.0) 43.2 (±0.8) 9.6 (±0.9) 69 (±6)
Early-season drainage [E] 4.4 (±1.0) 44.7 (±10.3) 9.9 (±2.2) 40 (±13)
Midseason drainage [M] 4.3 (±1.6) 56.0 (±3.2) 10.9 (±1.8) 34 (±8)
Pre-season plus midseason
drainage [PM]
6.3 (±2.0) 34.7 (±3.5) 8.7 (±0.7) 76 (±2)
Early-season plus
midseason drainage [EM]
4.0 (±0.5) 56.3 (±3.0) 8.3 (±1.1) 47 (±3)
§ The P and PM water
treatments resulted in higher
plant biomass (>6 g pot-1) as
compared to C, E, M and EM
treatments
§ The C and M treatments
resulted in higher GWP than
the other treatments

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4. Conclusions
ü The present study indicates that pre-season drainage and early-season drainage
alone, or in combinations with midseason drainage (PM and EM) are an effective
drainage practices to reduce 57 % to 87 % contribution of straw-derived carbon
in CH4 emissions, which substantially reduced the total GWP by 18 % to 31 %
compared to continuous flooding.
ü The present study suggests that drainage in the early stage of residue
incorporation (pre-season or early-season) has potential to mitigate the CH4
emissions from potential labile (straw) carbon sources in flooded rice system

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5. Acknowledgements
I would like to thank Professor Andreas de Neergaard, Ph.D. student Azeem
Tariq at the University of Copenhagen, Organization CCAFS (Climate Change,
Agriculture, and Food Security Program) via a CLIFF grant (The Climate Food
and Farming Network) for technical assistance and financial support.

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THANK YOU
FOR YOUR
ATTENTION!