The Climate Food and Farming (CLIFF) Research Network is an international research network that helps to expand young researchers' knowledge and experience working on climate change mitigation in smallholder farming. CLIFF provides grants for selected doctoral students to work with CGIAR researchers affiliated with the Standard Assessment of Mitigation Potential and Livelihoods in Smallholder Systems (SAMPLES) project. This presentation is Drainage of Flooded Rice Soil Influence the Residue Carbon Contribution in Methane Emissions by Phan Hữu Thành, at the Institute for Agricultural Environment, Vietnamese Academy of Agriculture Sciences, in Hanoi, Vietnam.

1. 1
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

2. 2
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

3. 3
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)

4. 4
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

6. 6
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

7. 7
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

8. 8
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)

9. 9
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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5
10
15
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35
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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(‰)

10. 10
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
11
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

13. 1313
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!