An Appraisal of Methane Emission of Rice Fields from Kerian Agricultural Scheme in Malaysia
Methane (CH4) emission from rice field at Kerian Agricultural Scheme, Perak, Malaysia was evaluated to ascertain its effect on rice yield with respect to water management and climate change mitigation strategies. A closed gas chamber technique was used for gas entrapment, sampling bag for collection and portable gas analyzer (GA2000) was used to detect CH4 and other gases. The measurement was conducted on hourly basis with 10 min intervals in a week at different growth stages of rice cultivation. Other soil and water analyses were carried out using standard procedures. The CH4 emission was not detected during the selected rice growing season due to the timing of measurement, however CO2 ranged between 0.1 and 1.2%, O2 between 17 and 20%, inert gases 78.9 and 81% and H2S between 5 and 14 ppm. Other factors that had indirect effects on the CH4 emission which were determined included the soil type, water level and type of fertilizer applied which depended on SO42¯ or NO3¯ constituents.
Received: January 20, 2012;
Accepted: March 05, 2012;
Published: June 26, 2012
One of the most serious long-term challenges facing the world today is climate
change and the most affected sector is agriculture since climate is the primary
determinant of agricultural productivity (McCarl et al.,
2001). Atmospheric methane (CH4), nitrous oxide, (N2O)
and carbon dioxide (CO2) are the major Greenhouse Gases (GHG) that
had potential of contributing to global warming (Tsuruta,
2002). However, an attempt to reduce GHG emission is likely to mitigate
such impacts on food production especially rice (McCarl et
Rice, the major staple food in Malaysia and the most important source of rural
employment and income generation is being threatened by yield reduction occasioned
due to the global effects of climate change. It is one of the most important
cereal crops, with over 170 million ha under cultivation globally and grown
in wide range of climatic zones (Singh et al., 2011).
South and southeast Asia are generally accepted and regarded as origin of Rice
and Malaysia belongs to these regions (Bounphanousay et
al., 2008). Rice is the third most important crop in Malaysia after
rubber and palm oil in terms of production and productivity which is mainly
grown in the eight granary areas in Peninsular Malaysia covering an area of
about 209,300 ha (Akinbile et al., 2011). The
two major rice growing areas are Muda Agriculture Development Authority (MADA)
and Kemubu Agriculture Development Authority (KADA) and the latter was only
able to produce 230,000 tonnes of rice while it was expected to increase to
260,000 tonnes in 2010 (Akinbile et al., 2011).
It has been predicted that Malaysian rice production will reduce by 0.36 t ha-1
to a 2°C temperature rise and will cause the economy loss of Malaysian Ringgit
(RM) 162.531 million per year (Vaghefi et al., 2011).
Similarly for the increase in CO2 from the current concentration
level of 383 to 574 ppm, a decline in rice yield of about 0.69 t ha-1
will be incurred, economic implications of RM 299.145 million per year (Vaghefi
et al., 2011). Tsuruta (2002) reported that
methanogenic bacteria in paddy soils under anaerobic conditions facilitate CH4
emission from rice fields during flooded and rice growing season. Rice fields
are one of the major anthropogenic sources on methane (CH4), a greenhouse gas
to the atmosphere. The CH4 concentration is expected to increase
further due to expansion of rice cultivation (Singh and
Singh, 1995). Yue et al. (2010) also established
that CH4 flux was high during flooding while N2O was emission
was small. Other Greenhouse gases (GHG) such as (CO2) and (N2O)
have significant effect on yield as their emissions were the strongest in rice
fields. The concentration of CH4 increased by 4.9 ppb/year and N2O
by 0.8±0.2 ppb/year and this has affected yield in rice production (Yue
et al., 2010).
Several rice varieties were developed and cultivated in Malaysia rice fields.
The commonly grown varieties were MR211, MR219, MR220 and MR232. However, the
Kerian Agricultural Scheme (KAS), which is located at Perak state in Peninsular
Malaysia, is grown MR219. Such variety is a hybrid type of MR137 and MR 151
varieties. Due to cross-hybridization, MR 219 is having improved plant morphology
and good rice texture with uniformity of ripening on the stalks to achieve high
yield over original local varieties (MAEP, 2010). Several
research works such as (Towprayoon et al., 2005;
Khalil et al., 2000; Chakraborty
et al., 2000; Tyagi et al., 2004;
Purkait et al., 2007; Naser
et al., 2007; Pathak et al., 2005)
had been carried out on GHGs on rice fields in most part of Asian continents
in countries such as Thailand, China, Japan, India and Sri Lanka however, considerably
fewer research works were conducted in Malaysia. Therefore, the aim of the study
was to determine methane and other gases emissions from rice field at Kerian
Agricultural Scheme as well as to ascertain the effect of control factors on
the emissions on the paddy fields under the same conditions.
MATERIALS AND METHODS
Study area characteristics and pre-measurement activities: The KAS, located at the northwest of Perak State in Peninsular Malaysia, is one of the oldest irrigation schemes in Malaysia. It has an area of 23,800 ha was divided into eight irrigation compartments, which were further divided into a total of 28 blocks (Fig. 1). It covered 24,100 ha of rice cultivable land and over 19,000 rice farming families those practicing double cropping of rice for their livelihood. The primary source of irrigation supply for the KAS is from the Bukit Merah Reservoir having a total storage capacity of approximately 75 million cubic meters (m3) of water. The Bukit Merah Reservoir with an active storage capacity of 56 million m3 collects runoff from a 489 km2 catchment. The Bogak Pumping Plant supplements irrigation water supply through the main canal (Terusan Besar), from Bukit Merah Reservoir, which was split into the three sub-branches namely, Terusan Alor Pongsu, Terusan Tg. Piandang and Terusan Serong.
The soil type is clayey soil with pH ranging from 4.0 to 6.5, Cation Exchange Capacity (CEC) is higher than 20 meq/100 and C: N ratio of 6.28 with nitrogen (N) 10 g kg-1 and total Carbon (C) 62. 8 g kg-1, respectively. The scheduled management activities followed conventional procedures which included Integrated Pest Management (IPM), diseases control and fertilizer application using the mixture of urea and N-P-K as 15-15-15. The MR219 rice variety was planted using direct sowing method.
|| Kerian irrigation scheme map
Sampling and on-site measurement method: Static-chamber method (Naser
et al., 2007) was used in collecting GHGs from the rice fields. Two
transparent, rectangular Gas Chambers (GC) (with size 51x51x100 cm) constructed
using 10 mm thickness transparent perspex materials and placed in the rice plants.
The internal temperature of the GC was measured with thermometer attached inside
the chamber. A silicon tube with valve was also attached to each chamber for
gas sampling and in-situ measurement. A miniature electronic fan was attached
to each of the GC to increase air circulation during measurement. In-situ measurement
of the gas was carried out in the two gas collection chambers between 1000 and
1500 h weekly for one hour at 10 min intervals for the two sampling points.
Sampling was conducted weekly and recorded according to the paddy growing stages.
The GCs were installed at the respective sites at least 24 h before each measurement
was conducted and were uninstalled from the sites 24 h after the measurement
to allow conventional agricultural practices and development take place.
Although, the most commonest equipment for measuring gas generally is a laboratory Gas Chromatograph (GC) which has detectors and different sizes of columns depending on the type of gas to be determined, however for this in situ measurement in this study, a portable gas analyzer (model: GA 2000 Geotechnical Instrument-UK Ltd) was used for direct measurements. The GA 2000 measures CH4, CO2, O2, H2S and H2 at the real-time basis and is expressed in percentage of the air within the gas chamber. Specialized polyethylene sampling bags (gas samplers) were used to collect gas from within the gas chamber before measurements took place.
Data analysis: Methane gas (CH4) emissions were determined
from the increase or decrease of gas concentration in the gas chamber per time
using the equation adopted from (Naser et al., 2007)
as given below:
where, F is the gas emission, ρ is the density of gas at the standard condition (CH4 = 0.716 kg m-3), V(m3) and A(m2) are the volume and base area of the chamber, respectively Δc/Δt (10-6 m3 m-3 h-1) is the gas concentration change in the chamber during a given period, T is the absolute temperature (K) and α is the conversion factor for CH4 to C (12/16).
This was however different from the approaches of Li (2000),
Li et al. (2004), Jiao et
al. (2006), Ma et al. (2009) and Yue
et al. (2010) which adopted the more traditional Gas Chromatograph
(GC) approach. The major setback in the GC approach, according to Streese-Kleeberg
et al. (2009) was its inability to measure GHGs in situ. The use
of Gas Analyzer was due to its availability and ability to determine the gases
in situ. Methane emissions behavior was correlated directly with the local agricultural
practice and the fluctuations of its limitations factors which included the
water level, soil type and also the type of fertilizer applied. Akinbile
and Yusoff (2011a) also confirmed the relationship between Methane emission
and fertilizer applied.
RESULTS AND DISCUSSION
Table 1 showed the fives gases that were determined in-situ
using gas analyzer (GA2000) and other related information such as the stage
of paddy growth at the period of measurement, sampling date, Days After Sowing
(DAS), water level and undetermined gases. The stages considered included, harvesting,
sowing, emergence and tillering while the gases measured also included CH4,
CO2 and O2 emissions from the field at these stages. Methane
gas was not detected throughout the entire planting season which might be due
to the time of the day when measurements were carried out. Naser
et al. (2007) and Purkait et al. (2007)
reported that maximum gas (including CH4) could be determined before
the sunrise and after the sunset. At these periods, the emissions would still
be measurable due to the absence of heat that dispersed the gas whenever the
sun is shining. Conrad (2002) and Chakraborty
et al. (2000) underscored the role of temperature in achieving most
reliable measurements since the gases are extremely sensitive to heat. Similarly
from the Table 1, the CH4 was not detected during
the harvesting stage which perhaps was due to the non-flooding condition of
the paddy field at that stage. Mosier et al. (2004)
and Matthews et al. (2000) reported that methane
production during under upland rice cultivation or in periods when lowland was
not flooded would almost be zero since the water level is zero meaning there
was no water at all in the field. Akinbile and Yusoff (2011b)
made similar observations in their study using different crop.
During the sowing stage, the field was flooded by water two weeks before the
seedlings were sown. This was for the land preparation purposes and also, insecticides
had been applied to the field one week before sowing. Also, from the results
presented in Fig. 2, there was negligible methane detection
during this stage.
|| Gases measurement and associated information
|Fig. 2 (a-d):
||Methane gas measurement during (a) Harvesting (b) Sowing (c)
Emergence and (d) Tillering stage on KAS paddy field
This might be correct theoretically as 90% of the methane gas was transported
via rice stalks as reported by Kyuma (2004) and Kern
et al. (1997). Apart from this, ebullition and diffusion only contributed
a small amount of methane emissions from paddy field. Since it was just the
sowing stage without any well-developed rice stalks, methane production would
naturally be low and this view was supported by Wassmann
et al. (2000) and Schimel (2000). On the
whole, no methane gas was detected in all the four stages and several reasons
were given for this situation one of which is the soil factor which is clay.
||Percentage composition of CO2, O2 and
unknown gases on paddy field according to growing stage
Kyuma (2004) found out that west Malaysian soil taken
from coastal lowlands are clayey and contain moderate amount of silts. Thus,
oxidation of methane might occur as reported by Le Mer and
Roger (2001) that clay soils might have entrapped more methane which increased
the probability of oxidation and in that circumstance, low methane emissions
would be experienced. Since, low methane gas was produced, there was a probability
that the little produced may have been oxidized before its emission to the atmosphere
took place which must have led to reduction in the methane flux. Boeckx
et al. (2005) reported that production rate would be higher than
emission rate because it was most unlikely that all the CH4 produced
would be emitted into the atmosphere. Some would be oxidized by the reaction
of methanotrophic bacteria or oxygen in the atmosphere and also by the photosynthesis
activities of benthic organisms. In the case of India, Purkait
et al. (2007) remarked that irrigated areas in India were subjected
to Alternate Wetting and Drying (AWD) cycles and most of the methane gas were
oxidized before reaching the soil-air interface resulting in lower methane flux
and uptake by the rice soil. Similar observations were observed by Salam
and Kato-Noguchi (2010) in Bangladesh during the study similar to this.
Akinbile et al. (2012) also reported on Bangladesh
rice that apart GHG, Arsenic contamination was very prevalent and inhibit tremendously
growth and yield.
Apart from these, factors which control methane gas emissions such as temperature,
pH and sulphate concentrations were prone to make its emissions to fluctuate
tremendously for in-situ study and may have affected the flux as well
(Neue et al., 1997). These factors were assumed
to have affected methane gas emissions resulting in its sinks in this study,
due to unstable control factors and soil disturbances during the in-situ measurements.
The percentage composition of other gases detected by the GA 2000 such as CO2,
O2 and unknown gases were as shown in Fig. 3. There
was gas emission in all the stages except during the tillering stage and the
highest CO2 emission was recorded during the harvesting stage when
the field has been drained, preparatory for harvest. The CO2 value
of 1.2% was recorded. Conventionally, rice respires by producing CO2
in the day before sunrise and O2 at night after sunset. The measurements
at the strength of sunshine might be responsible for the very low quantity of
CO2 recorded during the experiment. The effect of water level on
the CO2 emission was not visible as there were emissions during harvest
when the water level was zero as well as in sowing when the water level was
at maximum however; the growing stage had measurable impact on the gas emission
as CO2 was not detected only during tillering stage.
|| Hydrogen sulphide (H2S) gas detected in the gas
Pathak et al. (2005) reported that CO2
and CH4 could only increase considerably if more roots and shoots
growth of rice with more N fertilizer application would produce more amounts
of root exudates larger amounts of root debris which supplied C as substrate
heterotrophic microbes resulting in larger emissions of these gases. This was
supported by Tiwari et al. (2011), Philips
and Podrebarac (2009), corroborating the observations recorded from this
study. Oxygen was present in detectable quantities at all the different growing
stages and this was due to the electric fan installed to circulate the air within
the gas chamber before taking the measurements. It ranged between 18.2 to 20%
in all the stages. The largest portions of the gas within the chamber were unknown,
with the exception of hydrogen sulphide, due to the inability of the GA 2000
to detect it. It ranged between 79.9 to 80.2% in all the growing stages and
the probability that the unknown gas was inert was high due to its low reactivity.
The quantities of hydrogen sulphide, H2S as detected by GA 2000
during some growing stages in the KAS rice fields were as presented in Table
2. A sudden increase was recorded from first to fourth day after sowing,
i.e., from 5 to 14 ppm and that was sustained through to tillering and for the
next six weeks of experiment, though with a very marginal fluctuation of 13
ppm (Table 2). The amount of H2S was quite high
after sowing and application of pesticides to control mollusk until the tillering
stage and H2S toxicity might have occurred in soils due to low active
iron and in parts of fields which had been enriched by organic substrates. Such
scenario agreed with the findings of Jackel and Schnell
(2000). The H2S is a type of gas that emits bad odour and promotes
corrosion produced from the reduction of SO42¯. The
severity of H2S toxicity is common in coastal peats which dry-out
seasons between periods of flooding (Neue et al.,
1997). Other toxic substances produced during the decomposition of organic
matter at low redox potentials are thiols, organic sulphides, H2S
and C2H4 and there was a relationship between sulfate
concentration in soil and CH4 production rate. The higher sulphate
concentration would result in lower CH4 production since H2S
was produced on reduction of sulphate with oxidation of CH4 during
the process. There was the likelihood of competition between methanogenesis
micro-organisms and sulphate-reducing bacteria. Normally in these conditions
sulphate-reducers win which would result in less methane (Mukherjee
et al., 2009) because CH4 was oxidized during the sulphate
reduction by the bacteria (Meijide et al., 2010).
Although, NH4+SO42¯ caused
root rot in rice by producing hydrogen sulphide, it might effectively affect
rice production and subsequently CH4 emission (Minamikawa
et al., 2005). It was reported by Le Mer and
Roger (2001) and Fukushima and Chen (2009) that
NH4+SO42¯ was the substrate which was
suitable to control CH4 emissions from rice soil. Most of the trace
gases from rice fields were unknown gases, which could be inert gases. It covered
80% of the overall air contents in the chamber and might also contained some
of the greenhouse gases that retard rice yields but were not detected due to
the timing of measurement. One thing that is however abundantly clear is that
the effect of these GHG emissions from KAS rice fields negatively affected production
and yield under any given circumstances.
An attempt was made to determine methane emissions on rice fields at KAS, Perak, Malaysia. Besides, the effect of two other greenhouse gases namely carbon dioxide and hydrogen sulphide were determined from the same field. From the study, there was no detection of methane emission during the four growing stages of paddy rice development. Previous studies confirmed low methane detection during those four stages, resulting in low emissions, however, it was reported that significant CH4 might be detected during heading and ripening stages of rice production which was not considered during this study. Similarly, the timing of measurement was reported to have a direct effect on the CH4 readings. In the same manner, the water level, soil type and type of fertilizer applied had been proved to have considerable effect towards emission of CH4 and other gases from the rice fields. While methanogenesis formation reduced soil with very low Eh condition to produce methane, this occurred only during flooding period, clayey soil promotes methane oxidation which resulted in lower methane emission. It has been established that soil is the main source for methane production and emission and also good methane sink medium. Similarly, while nitrogen fertilizer promotes methane emission, sulphate fertilizer promotes methane oxidation which reduces methane emission. This is also an important control factor for methane emission in the rice fields. Other GHGs such as CO2 and H2S were also detected in small quantities indicating their low emissions from KAS rice field under flooded conditions. The CO2 ranged from 0.1 to 3% while H2S was between 5 and 14 ppm throughout the entire experimentation. Further research on methane emissions is crucial in other to develop the significant databank on methane emissions from rice fields in Malaysia. Moreover, further research to comprise all the planting stages is needed to be able to observe the actual trend of methane emissions in the selected sites. It was also suggested that different fertilizations plot experimentation might be an alternative to evaluate the effects of chemical fertilizers on the emissions of methane and other GHGs. Finally, the need to consider another important GHG, nitrous oxide (N2O) and GHG emissions under different irrigation management scenarios with respect to yield is also proposed.
The authors are most grateful to the Third World Academy of Science (TWAS) for providing one year Post Doctoral fellowship for Dr. Christopher Oluwakunmi AKINBILE (FR Number: 3240223476) and Universiti Sains Malaysia (USM) to enable him utilize the fellowship in conducting this study at USM.
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