International Journal of Scientific and Research Publications, Volume 8, Issue 8, August 2018 649

ISSN 2250-3153

Evaluation of Different Rates of Organic Manure and

Water Management Practices on Methane Emission
from Rice Production
Ei Phyu Win*, Kyaw Kyaw Win, Kyaw Ngwe, Than Da Min
*Corresponding author: eiphyu000@gmail.com

DOI: 10.29322/IJSRP.8.8.2018.p8083
http://dx.doi.org/10.29322/IJSRP.8.8.2018.p8083

Abstract: To find out the water management and organic manures practices to obtain minimum methane emission, the
pot experiments were conducted during the summer and rainy season 2017. Split plot design with three replications was used.
Two water management practices and four cowdung manure rates were allocated in main and sub factor arrangement. IR 50 was
planted with twenty one seedling age. In summer season, the gas sampling at 8 DAT expressed the second largest amount of
methane emission. At 14 DAT, the largest methane emission was found. At later DATs until harvest, the smaller amount of
methane emission was recorded. Numerically, the higher methane emission was observed from CF over AWD. The surface water
pH was highly statistically correlated with methane emission. In continuous flooding, the highest methane emission was recorded
from OM3 and the lowest emission from OM0. In alternate wetting and drying (AWD), the higher methane emissions were
recorded from OM0 and OM3 and the lowest emission from OM1. In rainy season experiment, there was statistically different in
methane emission among the water management. CF gave the higher methane emission at every gas sampling over AWD
practice. The surface water pH was highly correlated with methane emission. In continuous flooding, the highest methane
emission was observed from OM2 and the lowest emission from OM0. In alternate wetting and drying practice, the highest
methane emission was recorded from OM0 and the lowest one from OM3.

Key words: rice, organic manure, water management, methane emission

1. Introduction
Globally rice is a crucial crop: it has a central role in providing food, it has a central role in providing employment, and it
has substantial environmental impacts. Globally rice is estimated to be responsible for 19% of anthropogenic methane emissions,
second only to ruminants (Chen and Prinn 2006).
Most of the world’s rice grows in inundated conditions, and one of the most promising techniques for reducing rice-
related emissions is to reduce or interrupt the periods of flooding. The production of rice in flooded paddies produces methane
because the water blocks oxygen from penetrating the soil, creating conditions conducive for methane-producing bacteria.
Methanogenesis, methane production, is a microbial process strictly limited to anaerobic conditions (Ma et al. 2010).
Methane is produced from the respiration of organic matter in anaerobic conditions. Given the existence of abiotic
conditions in a paddy soil, the supply of methanogen substrate – soil organic matter – is the commonest limiting factor for
methanogenesis (Yao et al. 1999; Wang et al. 2000). Organic matter typically arise from four sources – three imported or easily
controllable sources: animal manure, green manure and crop residues (straw, stubble, roots), and one by-product of rice
production – this year’s root exudates, sloughed off root cells, root turnover. The addition of 5t rice straw ha -1 increased CH4
emissions tenfold compared to the use of urea alone (Neue et al. 1996), and the CH 4 reductions associated with alternate irrigation
was lost when rice straw was added compared to continuously flooded paddy, measured per tonne of paddy (Adhya et al. 2000).

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Rice farmers tend to keep their fields continuously submerged to control weeds, although long-term experiments suggest
that continuous puddling for rice destroys soil physical properties and affects both the puddled rice yield and the following crop
negatively (http: //www fao org/teca/content/alternatives-rice-puddlingand-transplanting). Rice environments with an insecure
supply of water, namely rainfed rice, have a lower emission potential than irrigated rice.
Alternate Wetting and Drying (AWD) is a water-saving technology that lowland (paddy) rice farmers can apply to
reduce their water use in irrigated fields. Hence, the field is alternately flooded and non-flooded. The number of days of non-
flooded soil in AWD between irrigations can vary from 1 day to more than 10 days depending on the soil type. Water savings
may be up to 15-25 percent with no yield penalty. The AWD promotes good root anchorage, thus reduction in plant lodging
problems. The AWD reduces 30-70 per cent of methane emissions depending on the combination of water usage and management
of rice stubble (FAO 2013).
Methane emission depends on soil type, weather condition (i.e. temperature, rainfall), varieties, water management,
organic amendment and cultural practices. Nowadays human beings noticed well about the climate change and are alert in GHG
emission mechanisms. A little has been known the methane emission from paddy fields in the country. This study was, therefore,
carried out to investigate the methane emission from paddy field. The pot experiments were conducted in summer and rainy
season 2017 with the following objectives: to evaluate the performance of rice plant as affected by different rate of organic
manure and water management practice and to find out the suitable organic manure rate and water management practice on
methane emission.

2. Materials and Methods

The pot experiment was conducted at farmer's field in Si Taing Kan village tract during the summer and rainy seasons.
The pots were arranged in split plot design with three replications. The water management (continuous flooding (CF) and
alternate wetting and drying (AWD)) was arranged as main plot factor. Different rates of organic manure were assigned as subplot
factor. In this study, cowdung manure was applied as organic manure.
Soil was collected from paddy field to use as experimental pot soil. The soil and cowdung manure were analyzed at
Water Science Section, Water Utilization and Agricultural Engineering Division, Department of Agricultural Research (DAR).
The results of properties of soil and cowdung manure are shown in Appendix I. The meteorological data for the study period
(February to October) are shown in Appendix II.
2.1 Treatment application
The calculated cowdung manure according to treatments (OM 0 = no cowdung, OM1 = half of recommended cowdung
(2.5 tons ha-1), OM2 = recommended cowdung (5 tons ha-1) and OM3 = one and half of recommended cowdung (7.5 tons ha -1)
were put at seven days before transplanting. The recommended cowdung manure is 5 t ha-1 (4 cart load ac-1). Each pot received
the recommended fertilizer at the rates of 86.8 kg N ha -1, 30.2 kg P2O5 ha-1, 18.9 kg K2O ha-1. Urea, T-super and Potash were used
as nutrient element sources. Urea was applied as three equal splits at active tillering, panicle initiation and heading growth stages.
T-super was applied only as basal at one day before transplanting and potash fertilizer was used for two equal splits at basal and
panicle initiation.
Field water tubes were installed in the AWD pots at a depth of 15 cm below the soil surface in between the seedlings and
base just after transplanting. For AWD pots, whenever there was no water in the field tube, irrigation water was applied until 5 cm
depth above the soil surface. The irritation interval ranged from 4 to 9 days and the amount ranged from 7 to 13 liters depending
on the different rates of cowdung manure in AWD pots. Withdrawal of water was started one week before the harvest period in all
water treated pots.

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2.2 Data Collection

Soil parameters
Surface water pH was recorded by using pH meter (HI8314, Hanna, Japan). Redox potential was taken by ORP meter
(HI8314 Hanna, Japan) with probes. Soil temperature was collected with waterproof digital thermometer (CT-300WP, Tokyo,
Japan). These parameters were recorded along with gas sampling time. Soil (15 g) was taken from soil surface of each pot for soil
pH analysis. Soil pH was analyzed at Department of Agriculture, Madaya using pH meter in 25:1 ratio of deionized water and
soil.
Gas sampling and calculation
Just after transplanting, the base was put to the gas sample plant to avoid the disturbance of the environmental conditions
around the rice plants during chamber deployment. The base was equipped with a water seal to ensure gas-tight closure. The base
remained embedded in the soil throughout the rice growing period. The two-binded chamber of total capacity of 77 L (93 cm
height) was used for collecting gas sample. The mouth of closed chamber had diameter of 41 cm. Therefore the diameter of
chamber base is wide to 40 cm with 3 cm wide-water seal. The chamber was painted with white color to prevent the absorption of
temperature. To thoroughly mix the gases in the chamber, the chamber was equipped with a small fan of 12 volt DC connected
with three 9-volts dry cells. For CH4 calculation, temperature was recorded with a digital thermometer (TT-508 Tanita, Tokyo,
Japan). For compensation of air pressures between increased temperature and gas sampling, an air buffer bag (1-L Tedlar bag)
was attached to chamber. The silicon rubber tube together with the soft vinyl tube (In dia 3mm x out dia 5 mm) attached with
double three-way stop corks was inserted air tight to a hole on chamber. The gas sample was taken with airtight 50 ml syringe by
inserting it to the three way stop cock. The 50 ml syringe was stroke 5 times for air cleaning before collecting of gas sample. The
air inside the chamber was thoroughly mixed by flushing the syringe three times before collection of the gas samples. The gas
sample was drawn to the 50 ml volume of syringe through the three way cock from chamber and then transferred to 15 ml
vacuum glass vial which were evacuated after adjusting the pressure to the 40 ml volume of syringe.
CH4 concentration was analyzed with a gas chromatograph (GC 2014, Shimadzu Corporation, Kyoto, Japan) equipped
with a flame ionization detector (FID). The amount of CH 4 flux was calculated by using the following equation;
Q = (V/A) x (∆c/∆t) x (M/22.4) x (273/K)
Where, Q = the flux of CH4 gas (mg m-2 min-1)
V = the volume of chamber (m3)
A = the base area of chamber (m2)
(∆c/∆t) = the increase or decrease rate gas concentration (mg m-3) per unit time
(min)
M = the molar weight of the gas,
K = Kelvin temperature of air temperature inside the chamber
Total emissions were calculated by multiplying the daily gas flux at each measurement for the time interval and summing up the
values for the growing period.
2.3 Statistical analysis
The data were analyzed by using Statistix (version 8.0). Mean comparisons were done by Least Significant Difference
(LSD) at 5% level.

3. Results and Discussion

Soil parameters during the summer season, 2017
Soil temperature: Different levels of organic manure application gave different mean values of soil temperature (Figure 3.1). In
continuous flooding, the start-up high temperature was found at 8 DAT due to the stimulation of organic manure in the soil. The

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high soil temperature was given by OM0 and the low soil temperature from OM2. It sharply decreased to minimum value
throughout the growing season at 14 DAT. This might be due to soil physiocochemical changes affected by weather. Khalil el al.
(1998) reported that during the growing season, the temperature changes was driven by diurnal cycles of sunlight and cycles of
soil temperature are sometimes observed as weather systems come and go. The high soil temperature was recorded from OM 0.
Then the soil temperature slowly increased until 34 DAT. At that time, the high soil temperature was found in OM 1 and the low
soil temperature from OM3. This could be due to the decomposition of organic matter. Again at 44 DAT, the soil temperature
slightly decreased (about 25 °C), which coincided with panicle initiation stage. From that stage, the soil temperature is gradually
increased until 64 DAT and then, decreased again at 74 DAT. From that, the soil temperature increased until harvest because of
substrate decomposition.
In AWD, the same trend of soil temperature was recorded. However, the peak soil temperature values were changed
depending on growth stages. At 8 DAT, OM3 gave high soil temperature, OM1 at 14 DAT, OM2 at later sampling dates.
The mean effects of soil temperature of different cowdung manure rates under both water regimes were not much
different. This result supported the finding of Haque et al. (2016) who stated that the soil temperature was slightly lower when the
paddy was flooded than when it was midseason draining. Xu and Hosen (2010) stated that the soil temperature was affected by
activity of methanogenic bacteria, the decomposition rate of soil organic matter.
Soil redox potential: The different trends of soil redox potential (Eh) of variation was observed in Figure 3.2. In continuous
flooding, the soil redox potential was observed between -350 mV and -100 mV. The low redox potential values were recorded
from OM1 at 8 and 14 DAT, OM3 at 24 DAT, and OM1 at 34 DAT. During the later growth stage, the redox potential was
relatively stable because of microbial process of organic substrates. But mostly low redox potential was given by OM3. Jain et al.
(2004) reported that in soil with high amount of organic matter, Eh falls to -50 mV and may then slowly decline over a period of a
month.
In alternate wetting and drying, the soil redox potential was in the range of -300 to 0 mV. The different trend of soil
redox potential was also found. In the early growth stage (8, 14, 24, and 34 DAT), mostly the low redox potential was recorded
from OM2 but in later growth stage, the high fluctuation was found. At 54 DAT, the low value was resulted from OM2. OM1 gave
low redox potential at 64 and 84 DAT, OM 3 at 74 and 94 DAT. This is due to the microbial process of organic matter. Ascar et al.
(2008) stated that some of abiotic environmental factors such as Eh are strongly influenced by biotic environmental factors.
The mean effects of soil redox potential to different cowdung manure rates were different in both water regimes. After
flooding the rice field, the soil Eh values decreased sharply in both continuous flooding and alternate wetting and drying practice
within 2 weeks of rice transplanting (Haque et al. 2016). The cowdung manure affected the soil redox potential especially in the
continuous flooding. The higher cowdung manure caused the higher reduction condition in the soil. According to the report of
Nieder and Benbi (2008), application of organic matter will decrease Eh depending on the degree of humification.
Surface water pH: Different mean values of surface water pH were resulted from different levels of organic manure application
(Figure 3.3). The values of surface water pH were decreased at 14 DAT and thereafter increasing trends were observed upto 44
DAT. At each DAT, different level of organic manure application showed different values of surface water pH. It was observed
that mean values of surface water pH were higher in the early growth stages (from 8 to 64 DAT) as compared to those in the later
growth stages (from 74 to 94 DAT) under continuous flooding. This may be due to the microbial breakdown of organic substrates
in the early stages and depletion of them in the later growth stages. Gambrell (1994) and Guo et al. (1997) have reported on the
influence of soil microbial activities on pH. Zoltan (2008) stated that solute macro- and microelement content may influence on
spatial and seasonal variations of surface pH.
Like under continuous flooding, similar trend was observed under AWD. At each DAT, different values of surface water
pH were resulted from different levels of organic manure application.

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In comparison of both CF and AWD, the pH values under CF were generally higher than those under AWD during 24 –
44 DAT. This period ranged in panicle initiation stage. This increased pH value in CF may be due to the rapid decomposition
process by active microbes in the favor of organic substrates in that stage. It was obvious that the range of surface water pH under
CF was more wider than that under AWD because some of abiotic environmental factors was strongly influenced by biotic
environmental factors, which are also influenced by cultural practice such as water management (Ascar et al. 2008). Oo et al.
(2015) found high standing water pH in submerged rice soil. Zoltan (2008) reported that difference in water regime is one of the
most important abiotic factors for pH variations.
Soil pH: Different mean values of soil pH were observed in different levels of organic manure application (Figure 3.4). The
values of soil pH were decreased to 44 DAT and thereafter sharply increasing trends were observed upto 94 DAT except at 84
DAT which showed rapidly decreased. At each DAT, different level of organic manure application showed different values of soil
pH. It was observed that mean values of soil pH were lower in the early growth stages (from 14 to 44 DAT) as compared to those
in the later growth stages (from 54 to 94 DAT) under continuous flooding. In the early stage of irrigation, neutralized soil
condition was resulted because of active microbial process with trapped oxygen.
Like under continuous flooding, similar trend was observed under AWD. Mean values of soil pH were different in
different levels of organic manure at each growth stage.
In comparison of both CF and AWD, it was noticed that the soil pH values under CF were generally slightly lower than
those under AWD throughout the growing season. The AWD showed slightly alkaline condition. Some microorganisms such as
methanotrophs developed in the presence of oxygen and organic substrates, and kept the soil under slightly alkaline condition.
Mer and Roger (2001) reported that methanotrophs are ubiquitous in ricefield soils, where their densities were not strongly
affected by oxidation status of soil.

Methane emission during the summer season, 2017

The different amounts of methane emission were observed in the present study (Figure 3.5). In continuous flooding, at 8
DAT, the high methane emission was found, and then it was dramatically increased to highest emission at 14 DAT. This was due
to the intrinsic methane production potential of soil and rapid decomposition of cowdung manure. Zou et al. (2005) mentioned
that when the field was waterlogged, CH4 emissions ascended steadily until the peak fluxes were attained approximately 25 days
after rice transplanting. Rennenberg et al. (1992) reported that the first emission maxima, observed shortly after flooding, could
be attributed to the degradation of organic matter present in the soil. In the present study, small amount of emission was observed
in later growth stages to harvest. This might be due to impedition of methanogenic activity and limited carbon source for
methanogens. In general, the high methane emission was recorded from OM 3 at all DAT, and the low methane emission was
mostly resulted from OM0. Khosa et al. (2010) stated that application of organic materials to rice fields significantly increased the
rate of methane emission as compared to control plots receiving only inorganic fertilizer as the addition of organic matter
selectively enhanced the growth of particular methanogenic populations by providing them carbon source.
In AWD, the same trend of methane emission was observed. The most high methane emission was resulted from OM 2
and low methane emission from OM1. The mean values of methane emission in different cowdung manure rates were not
different in both water regimes. The methane emission ranged from 0.22 to 511.93 mg CH 4 m-2 in continuous flooding and 0.03 to
372.25 mg CH4 m-2 in AWD. Alternate wetting and drying reduce the amount of time rice fields are flooded and can reduce the
production of methane by about 60% or even up to 90% (IRRI, 2009). The total CH4 emission from intermittently irrigated fields
was found to be 22% lower as compared with continuous flooding (Jain et al. 2000). Alternate wetting and drying results in a
significant reduction of CH4 emission, and water drainage and resulting aerobic soil conditions allow the oxidation of CH 4 and
avoid CH4 production (Hussain et al. 2014). Katayanagi et al. (2012) reported that alternate wetting and drying has the potential to
reduce CH4 emission by 73 % compared with traditional flooded rice.

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Mean values of cumulative methane emission of rice were different in different levels of organic manure (Table 3.1).
Higher cumulative methane emission (2645.6 kg CH 4 ha-1) was found in CF as compared to AWD (792.2 kg CH 4 ha-1). The high
organic manure rate gave higher amount of methane emission (1968.0 kg CH 4 ha-1) as compared to others. The mean values of
methane emission in different cowdung manure rates were not different in both water regimes (Figure 3.6). However, in concern
with water regimes, the higher methane emissions were recorded in CF plots as compared with AWD plots. In CF, the methane
emission was found increasing trend depending on the increased cowdung manure rates. Multiple aeration for 2-3 days at 3, 6,
and 9 weeks after initial flooding reduced CH4 emission by 88% and did not reduce rice yields compared with the normal
irrigation (Sass et al. 1992). Wassmann et al. (2000) reported that in alternate wetting and drying, the time intervals between dry
and wet conditions appear to be too short to facilitate the shift from aerobic to anaerobic soil conditions resulting in a significant
reduction of CH4 emission. Water drainage and resulting aerobic soil conditions allow the oxidation of CH 4 and avoid CH4
production. Katayanagi et al. (2012) reported that alternate wetting and drying has the potential to reduce CH 4 emission by 73%
compared with traditional flooded rice. Methane emission from the flooded paddy increases by applying different organic matter
sources. Methane production, oxidization and emission from the flooded paddy are highly affected by the added organic matter
(Jean and Pierre 2001). Application of organic materials to rice fields significantly increased the rate of methane emissions as
compared to control plots receiving only inorganic fertilizer as the addition of organic matter selectively enhanced the growth of
particular methanogenic populations by providing them carbon source. The organic materials significantly increased the organic
carbon content over the control (Khosa et al. 2010). Schutz et al. (1989), Yagi and Minami (1990), Sass et al. (1991), Cicerone et
al. (1992), and Neue et al. (1994) observed that organic amendments to flooded soils increase CH 4 production and emission by
enhancing the reduction of soils and providing carbon sources. Nayak et al. (2013) concluded that livestock manure application in
rice increased CH4 emission and soil organic C sequestration while considerably decreased N 2O emission.

(a) Continuous flooding (b) Alternate Wetting and Drying

34 34

OM0 OM0
32 32
OM1 OM1
Soil temperature (°C)
Soil temperature (°C)

OM2 OM2
30 30
OM3 OM3

28 28

26 26

24 24

22 22

20 20
8 14 24 34 44 54 64 74 84 94 8 14 24 34 44 54 64 74 84 94

Days after transplanting Days after transplanting

Figure 3.1: Variation in soil temperature (a) continuous flooding and (b) alternate wetting and drying during the summer
season, 2017

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(a) Continuous flooding (b) Alternate Wetting and Drying

50 50

0 0
8 14 24 34 44 54 64 74 84 94 8 14 24 34 44 54 64 74 84 94
-50 -50
OM0 OM0
OM1 OM1
-100 -100
OM2 OM2

Soil Eh (mV)
Soil Eh (mV)

-150 OM3 -150 OM3

-200 -200

-250 -250

-300 -300

-350 -350

-400 -400
Days after transplanting Days after transplanting

Figure 3.2: Variation in soil redox potential (Eh) (a) continuous flooding and (b) alternate wetting and drying during the
summer season, 2017

(a) Continuous flooding (b) Alternate Wetting and Drying

9.3 9.3
OM0 OM0
9.1 9.1

OM1 OM1
8.9 8.9

8.7 OM2 8.7 OM2

Surface water pH
Surface water pH

8.5 OM3 8.5 OM3

8.3 8.3

8.1 8.1

7.9 7.9

7.7 7.7

7.5 7.5
8 14 24 34 44 54 64 74 84 94 8 14 24 34 44 54 64 74 84 94

Days after transplanting Days after transplanting

Figure 3.3: Variation in surface water pH (a) continuous flooding and (b) alternate wetting and drying during the summer
season, 2017

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(a) Continuous flooding (b) Alternate Wetting and Drying

8.4 8.4

8.2 8.2

8.0 8.0

7.8 7.8
Soil pH

Soil pH
OM0
7.6 OM0
7.6
OM1
OM1
7.4 7.4
OM2
OM2
7.2 7.2
OM3
OM3
7.0 7.0

6.8 6.8
14 24 34 44 54 64 74 84 94 14 24 34 44 54 64 74 84 94
Days after transplaning Days after transplanting

Figure 3.4: Variation in soil pH (a) continuous flooding and (b) alternate wetting and drying during the summer season,
2017

(a) Continuous flooding (b) Alternate wetting and drying

1000 1000
950 950
900 900
850 850
800 800
750 750
Methane emission (mg CH4m-2h-1)

Methane emission (mg CH4m-2h-1)

700 700
650 650
600 600
550 OM0 550 OM0
500 500
OM1 OM1
450 450
400 OM2 400 OM2
350 350
OM3 OM3
300 300
250 250
200 200
150 150
100 100
50 50
0 0
8 14 24 34 44 54 64 74 84 94 8 14 24 34 44 54 64 74 84 94
Days after transplanting Days after transplanting
Figure 3.5: Methane emission of rice (a) continuous flooding and (b) alternate wetting and drying during the summer
season, 2017

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Table 3.1: Mean effects of water regime and the rate of cowdung manure applied on cumulative methane emission of rice
during the summer season, 2017
Treatment Cumulative methane emission (kg CH4 ha-1)
Water
CF 2645.6 a
AWD 792.2 a
LSD 0.05 1967.1
Manure
OM0 (0 t ha-1) 1692.7 a
OM1 (2.5 t ha-1) 1619.2 a
OM2 (5 t ha-1) 1595.7 a
OM3 (7.5 t ha-1) 1968.0 a
LSD 0.05 905.3
Pr>F
Water 0.0558
Manure 0.7974
Water x Manure 0.7822
CVa (%) 65.15
CVb (%) 41.87
Means followed by the same letter are not significantly different at 5% LSD.

3500 LSD0.05= 2139.4

3000
Cumulativemethane emission

OM0
2500
OM1
(kg CH4ha-1)

2000 OM2

1500
OM3

1000

500

0
CF AWD

Figure 3.6: Mean values of cumulative methane emission of rice as affected by water regime and the rate of cowdung
manure applied during the summer season, 2017

Relationship between methane emission and soil parameters during the summer season
Variation in seasonal methane emission from rice paddies are complex and differ among several reported studies.
Relationship between methane emission and soil parameters was observed in Table 3.2. From rapidly increase at the beginning of
the season, methane emissions show relatively increase in the vegetative phase peaking near panicle differentiation, a period of
rapid root development. Emission afterwards is relatively constant during the reproductive stage, and decrease during the late
grain filling because of root degradation. In this study, the methane emission was significantly not correlated with soil
temperature, soil redox potential and soil pH. A correlation with soil temperature has been reported in some studies (Schutz et al.
1989), but not in others (Cicerone et al. 1983; Neue and Sass 1994). However, it was significantly correlated with surface water
pH (Pr > F 0.01). The surface water pH significantly affected on methane emission (Table 3.2).

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Table 3.2: Relationship between methane emission and soil parameters during the summer season, 2017
ST EH SWPH SPH
ns ns
CH4 0.1297 -0.3683 0.5755** -0.0563ns
CH4 – Cumulative methane emission (kg ha-1)
ST – Average soil temperature (°C) EH – Average soil redox potential (mV)
SWPH – Average surface water pH SPH – Average soil pH

Soil parameters during the rainy season, 2017

Soil temperature: Different mean values of soil temperature were observed in different levels of organic manure application
(Figure 3.7). In continuous flooding, the start-up high temperature was found at 7 DAT. The high soil temperature was given by
OM2 and the low soil temperature from OM1. It decreased at 15 DAT. The high soil temperature was recorded from OM 2. Then at
24 DAT, the soil temperature increased and maintained level off until 54 DAT. Again at 64 DAT, it decreased to about 28°C.
This coincided with heading stage. From that stage, the soil temperature increased to maximum value at 84 DAT throughout the
growing season. At 94 DAT, it again slightly decreased. Most high soil temperature was observed in OM 2 and low soil
temperature was resulted from OM0.
In AWD, the same trend of soil temperature was recorded. The most high soil temperature was recorded from OM 2 and
low soil temperature was resulted from OM1.
The mean effects of soil temperature in different cowdung manure rates were not different in both water regimes.
Soil redox potential: The complex trend of soil redox potential (Eh) was observed in Figure 3.8. In continuous flooding, the soil
redox potential was observed between -378.67 mV and -77.00 mV. The low redox potential values were recorded from OM0 in
the early growth stage and from OM2 in later growth stage.
In alternate wetting and drying, the soil redox potential was in the range of -366 to 33 mV. The complex trend of soil
redox potential was also found. Mostly the low redox potential was recorded from OM0 and the high soil redox potential values
were resulted from OM3.
The mean effects of soil redox potential to different cowdung manure rates were not different in both water regimes.
However, the high soil redox potential was observed in AWD because of soil aeration. However in this study, the soil redox
potential is not an indicator for methane emission and it was not affected by water and cowdung manure rates on methane
emission.
Surface water pH: Different mean values of surface water pH were resulted from different levels of organic manure application
(Figure 3.9). In continuous flooding, the surface water pH ranges were higher in early growth stages than in later growth stages.
The high pH was recorded from OM3 at 7 DAT, OM2 at 15 DAT, OM0 at 24, 44, 54 DAT
and OM2 at 34, 64, 94 DAT. The low surface water pH was resulted most from OM 0.
In AWD, the different trend was found. The high surface water pH was observed in OM 0 at 7, 34, 94 DAT, from OM1 at
15, 24, 44 DAT and from OM3 at 54, 64, 74, 84 DAT. The most low surface water pH was resulted from OM 1 and OM2.
The surface water pH range was from 7.89 to 9.06 in CF and 8.13 to 9.09 in AWD throughout the growing period. In this
study, the surface water pH was affected by water and cowdung manure rates. The mean effects changes were found depending
on water regime and cowdung manure rates.
Soil pH: Different levels of organic manure application gave different mean values of soil pH (Figure 3.10). In the initial stage,
the soil pH was a little bit high and gradually decreased fluctuating in some points until harvest. The soil pH was not affected by
water regime. The high soil pH was resulted from OM 0, OM2 and OM3. The most low soil pH was observed in OM0.

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In alternate wetting and drying, the same trend of soil pH was observed. Mostly the high soil pH was recorded from OM 0
and the low pH from OM3.
In both water regimes, the mean effects of soil pH to different cowdung manure rates were not significantly different.
The soil pH ranged from 7.24 to 8.01 in continuous flooding and from 7.18 to 8.02 in AWD. In this study, the soil pH was not
affected by water and cowdung manure rates.
Methane emission during the rainy season, 2017
Different mean values of methane emission of rice were resulted from different levels of organic manure application
(Figure 3.11). In continuous flooding, at the start-up gas collection, a little increase of methane was recorded. In the middle
growth stage, the highest emission was found and gradually decreased to harvest. The decreased methane emission in the
beginning was due to restricted supply of organic substrates for methanogenesis. Two peaks of methane emission was recorded in
the middle stage; the first peak at 34 DAT and the second peak at 54 DAT. The first peak was dominantly resulted by
decomposition of soil organic matters which provide carbon source for methanogenic activity (Fazli and Man 2014). At the
second peak, the carbon source for methanogens were available from the plant related organic matters entering into the soil from
rice roots (Khosa et al. 2011). More carbon source was available for methanogenic activity at 54 DAT and thus resulted in higher
methane emission than 34 DAT (Neue et al. 1996; Gogoi et al. 2008). Methane emission decreased in the later growth stage
because of depletion of organic substrates for methanogen. The most high methane emission was resulted from OM 3 and low
methane emission was recorded from OM1 throughout the growing season.
In AWD, the same trend of methane emission was observed. The maximum methane emissions have been observed at
panicle initiation stage. This increase was in consequence of decomposition of root exudates, rice plants’ litters (Gogoi et al.
2008) and soil organic matters. The most high methane emission was recorded from OM0 and low methane emission was resulted
from OM3. Irrigation could affect methane emission pattern indirectly by influencing the availability of organic matters and
influencing microbial process of methane production in the soil (Fazli and Man 2014).
The cumulative methane emission of rice during the growing season was shown in Table 3.3. Significant difference of
methane emission was recorded among the water treatments at Pr > F 0.05. The higher emission (1597.6 kg CH 4 ha-1) was found
in CF as compared to AWD (542.7 kg CH4 ha-1). No significant difference among the cowdung manure treatments and no
interaction between the factors were also observed. In both water regimes, the mean effect of methane emission to different
cowdung manure rates was illustrated in Figure 3.12. In this study, the methane emission was affected by water regime. But the
cowdung manure rate did not affect on methane emission. Milkha et al. (2001) pointed out that quality and quantity of organic
materials influence CH4 formation. Small differences in the carbon balance between fields and seasons can result in large
differences of CH4 emissions.

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(a) Continuous flooding (b) Alternate Wetting and Drying

38 38

36 36

34 34

Soil temperature (˚C)

Soil temperature (˚C)

32 32

30 OM0 30 OM0
OM1 OM1
28 28
OM2 OM2

26 OM3 26 OM3

24 24

22 22

20 20
7 15 24 34 44 54 64 74 84 94 7 15 24 34 44 54 64 74 84 94
Days after transplanting Days after transplanting

Figure 3.7: Variation in soil temperature (a) continuous flooding and (b) alternate wetting and drying during the rainy
season, 2017

(a) Continuous flooding (b) Alternate Wetting and Drying

50 50

0 0
7 15 24 34 44 54 64 74 84 94 7 15 24 34 44 54 64 74 84 94
-50 -50

-100 -100
Soil Eh (mV)

Soil Eh (mV)

-150 -150

-200 -200

-250 -250

OM0
-300 OM0 -300
OM1
OM1
-350 -350 OM2
OM2
OM3
OM3
-400 -400
Days after transplanting Days after transplanting

Figure 3.8: Variation in soil redox potential (Eh) (a) continuous flooding and (b) alternate wetting and drying during the
rainy season, 2017

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(a) Continuous flooding (b) Alternate Wetting and Drying

9.3 9.3
OM0 OM0
9.1 9.1
OM1 OM1
Surface water pH

8.9 OM2 OM2

Surface water pH
8.9
OM3 OM3
8.7 8.7

8.5 8.5

8.3 8.3

8.1 8.1

7.9 7.9

7.7 7.7

7.5 7.5
7 15 24 34 44 54 64 74 84 94 7 15 24 34 44 54 64 74 84 94

Days after transplanting Days after transplanting

Figure 3.9: Variation in surface water pH (a) continuous flooding and (b) alternate wetting and drying during the rainy
season, 2017

(a) Continuous flooding (b) Alternate Wetting and Drying

8.4 8.4

OM0
8.2 8.2 OM0

OM1
8.0 8.0 OM1

OM2
OM2
7.8 7.8
OM3
Soil pH

OM3
Soil pH

7.6 7.6

7.4 7.4

7.2 7.2

7.0 7.0

6.8 6.8
7 15 24 34 44 54 64 74 84 94 7 15 24 34 44 54 64 74 84 94
Days after transplanting Days after transplanting

Figure 3.10: Variation in soil pH (a) continuous flooding and (b) alternate wetting and drying during the rainy season,
2017

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(a) Continuous flooding (b) Alternate wetting and drying

140 140
OM0 OM0
120
OM1 120 OM1
OM2 OM2

Seasonal methane emission (mg CH4 m-2h-1)

Seasonal methane emission (mg CH4 m-2h-1)

OM3 OM3
100 100

80 80

60 60

40 40

20 20

0 0
7 15 24 34 44 54 64 74 84 94 7 15 24 34 44 54 64 74 84 94
Days after transplanting Days after transplanting
Figure 3.11: Methane variation of rice (a) continuous flooding and (b) alternate wetting and drying during the rainy
season, 2017

Table 3.3: Mean effects of water and cowdung manure applied on cumulative methane emission of rice during the rainy
season, 2017
Treatment Cumulative methane emission (kg CH4 ha-1)
Water
CF 1597.6 a
AWD 542.7 b
LSD 0.05 737.19
Manure
OM0 (0 t ha-1) 1082.2 a
OM1 (2.5 t ha-1) 1016.9 a
OM2 (5 t ha-1) 1161.2 a
OM3 (7.5 t ha-1) 1020.3 a
LSD 0.05 372.11
Pr>F
Water 0.0254
Manure 0.8147
Water x Manure 0.7545
CVa (%) 39.22
CVb (%) 27.64
Means followed by the same letter are not significantly different at 5% LSD.

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OM0 OM1 OM2 OM3

Cumulative methane emission

2000
1800 LSD0.05 = 819.70
(kg CH4 ha-1)

1600
1400
1200
1000
800
600
400
200
0
CF AWD

Figure 3.12: Mean values of cumulative methane emission of rice as affected by water and cowdung manure applied
during the rainy season, 2017

Relationship between methane emission and soil parameters during the rainy season
Relationship between methane emission and other parameters was described in Table 3.4. In this pot experiment of rainy
season 2017, the methane emission was not significantly correlated with soil parameters (soil temperature, soil redox potential,
soil pH) except surface water pH. Methane was significantly negative correlated with surface water pH (Pr > F 0.01).

Table 3.4: Relationship between methane emission and soil parameters during the rainy season, 2017
ST EH SWPH SPH
ns ns
CH4 -0.2806 -0.3343 -0.7992** -0.1044 ns
CH4 – Cumulative methane emission (kg ha-1)
ST – Average soil temperature (°C) EH – Average soil redox potential (mV)
SWPH – Average surface water pH SPH – Average soil pH

4. Conclusion
According to these pot experiments, the methane emission was significantly correlated with surface water pH and the
methane emission was significantly higher in continuous flooding than alternate wetting and drying. The cowdung manure did not
significantly affect on yield and methane emission. However, its effect was influenced by water management.

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Appendix I. Physiochemical properties of experimental soil and cowdung manure

No. Analytical Item Unit Analytical Result
1 Soil pH 7.4 Moderately alkaline
2 Available N mg kg-1 50 Low
3 Available P mg kg-1 13 Medium
4 Available K mg kg-1 78 Low
5 Total N % 0.17
6 Organic matter % 1.8 Low
7 CEC cmolc kg-1 11 Low
8 Sand % 87
9 Silt % 4
10 Clay % 9
11 Textural class Loamy sand

No. Analytical Item Unit Analytical Result

Summer season Rainy season
1 Total N % 1.32 1.2
2 Organic carbon % 16 23.3

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Appendix II. Daily rainfall, maximum and minimum temperatures in Madaya township, Myanmar during the summer and monsoon rice growing
seasons, 2017

Rainfall Temp. (max) Temp. (min)

50 120
45
100
40
35
Temperature (°C)

80

Rainfall (mm)
30
25 60
20
40
15
10
20
5
0 0
1 6 11 16 21 26 3 8 13 18 23 28 2 7 12 17 22 27 2 7 12 17 22 27 1 6 11 16 21 26 1 6 11 16 21 26 31 5 10 15 20 25 30 4 9 14 19 24 29 4 9
Feb Mar Apr May Jun Jul Aug Sep Oct

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