Methane Gas Emission From Irrigated Paddy Fields Environmental Sciences Essay

Abstract. The major focal point of this paper is to develop a distant feeling theoretical account to gauge methane gas emanation from irrigated paddy field. Initially the sum of methane gas emanation was collected through field experiments utilizing a closed chamber and farther analyzed to set up the rate of emanation at different phases of paddy growing. Simultaneously the spectral coefficient of reflection of paddy screen was besides measured utilizing spectrometer and Normalized Difference Vegetation Index ( NDVI ) was later calculated. Above-ground biomass was collected from the Paddy Fieldss to associate with rate of methane gas emanation and besides with NDVI. It was found that the rate of methane gas emanation was extremely related with NDVI and above-ground biomass. The peak period of emanation was at the maximal tillering to maximum flowering phase followed by worsening farther towards the crop clip. Based on the relationship with NDVI and biomass, the theoretical account is built to gauge methane gas emanation with higher grade of dependability that supports the usage of distant feeling technique replacing field measurings.

1. Introduction

Climate alteration or planetary heating is caused by the release of nursery gases into the ambiance. These gases accumulate in the ambiance and increase the consequence of radiative action on the clime, ensuing in a warming province of the ambiance. They absorb surpassing long moving ridge infrared radiation or heat energy, which the Earth and the ambiance usually radiate back to the outer infinite. These can do increasing in planetary temperature. Methane has profound impact on the physico-chemical belongingss in atmosphere taking to planetary clime alteration ( Dubey 2005 ) . It is recognized as one of the most of import nursery gases and may account for 20 per centum of awaited planetary heating ( Lindau et al.1993 ) . The rise in methane concentration is expected to increase the planetary mean temperature of the planet to the degree that may interrupt atmospheric, pelagic, ecological conditions and wellbeing of human existences. It has been estimated that the addition in methane concentration may hold contributed about 15 % to anthropogenetic nursery effects. The concentration of methane in the ambiance has more than doubled over the last 200 old ages, and in peculiar, has increased by approximately 50 % in the last 40 old ages ( Smakgahn et al.2003 ) . During the last 20 old ages, its concentration has been increasing, on an norm at the rate of 0.8 % per twelvemonth ( Prinn 1995 ) . Particularly, the agricultural sector is more than a receptor of possible climatic alterations originating from anthropogenetic nursery gas emanation ; it is every bit a beginning of methane responsible for approximately 40 % ( Zou et al.2004 ) . By far, the apprehension of agribusiness ‘s part to methane emanation has increased well over the last decennary.

Atmospheric methane originates chiefly from biogenic beginnings such as Paddies that account for 15-20 % of the universe ‘s entire anthropogenetic methane emanation ( Dubey 2001 ) . Rice is the universe ‘s most of import agronomic works with 153 million hectare under cultivation globally in 2004 ( IRRI 2006 ) . Approximately 55 % of cultivated rice is grown under irrigated paddy field conditions. In this sort of paddy field, paddy grows under flooded status and it leads to the emanation of methane ( Majumdar 2003 ) . The methane emanation is the net consequence of opposing bacterial procedures, production and ingestion in aerophilic microenvironments, both of which can be found side by side in afloat Paddy dirts.

There are many surveies have been conducted on methane gas emanation from several methods. Methane gas emanation from the country could be estimated by mensurating on the land. It was measured in situ by utilizing inactive chamber techniques during harvest growing period. Besides, it could be estimated by standardization and up scaling utilizing the theoretical account. Some research workers modified the widely used theoretical account and calibrated it with informations from rice Fieldss. And some theoretical account was linked to a GIS and used to cipher the one-year methane emanation from all major rice ecologies of the survey country. Some surveies estimated methane emanation by utilizing distant feeling techniques. It showed the utility of distant feeling techniques in generalizing land methane flux measurings to a regional graduated table estimation of methane emanation ( Tamura and Yasuoka 1995 ) .

Therefore, in this survey, it is attempted to find the methane gas emanation on rice cultivation and besides to develop distant feeling patterning for gauging methane gas emanation from irrigated Paddy Fieldss.

2. Objective of the survey

The aims of this survey are two creases: ( 1 ) to mensurate the sum of methane gas emanation at different turning phases of Paddy, and ( 2 ) to develop and formalize a distant feeling theoretical account to gauge methane gas emanation from irrigated Paddy Fieldss.

A series of field experiments present methane gas emanation appraisals from irrigated Paddy Fieldss in assorted rice ecosystems get downing from transfering phase to maturing phase. Then, this survey uses remote feeling technique in finding methane gas emanation from irrigated Paddy Fieldss in Suphanburi state of Thailand. It focuses on mensurating the sum of land methane gas emanation at different Paddy turning phases, developing and formalizing a distant feeling theoretical account to gauge methane gas emanation from irrigated Paddy Fieldss. The survey of methane gas emanation from irrigated Paddy Fieldss is necessary to understand and pull attending to work out the job of methane gas emanation, which is really common to explicate planetary heating.

3. Study Area

This survey was conducted in Suphanburi state of Thailand in 2004. It is located in the cardinal field of Thailand. It covers the country of about 5,358 km2. The geographic location of Suphanburi is between latitudes 14o 4? to 15o 5? N and longitudes 99o 17? to 100o 16? E. The height of the state ranges from 3 to 10 metres above the average sea degree. It is about 107 kilometres from Bangkok. It has 10 territories. The terrain of the state is largely low river fields, with little mountain scopes in the North and the west portion of the state. The southern portion is largely composed of tidal level terrain with low field of the Tha Chin River, covered by paddy Fieldss, about 2,500 km2 or 46 % of the entire country. Forest land exists on the West, northwest and some parts of the northern country. The clime of the survey country can be classified as Tropical Savannah ( Koppen ‘AW ‘ ) . It is typically wet and humid. The long rainy season extends for 6 months from May to October. Average humidness remains reasonably high between 75 and 80 % . The mean one-year rainfall is between 900 and 1,300 millimeter. The mean figure of showery yearss is around 109 per twelvemonth. The mean temperature ranges from 25o to 32oC. Three chief seasons can be distinguished ; a rainy season from May to October, a cool and dry season from November to February, and a hot and dry season from March to May. The country is level with clay dirt. Acid dirt is distributed over approximately 901 km2 ( 17 % of the survey country ) . Soil pH is instead strong to highly acidic. It gets flooded in the rainy season ( Land Development Department 1998 ) . The survey country is shown in Figure 1.

Figure 1. Study country: Suphanburi Province.

4. Method

Suphanburi-1, a local assortment of Paddy was cultivated under irrigated state of affairs. In the survey country, this assortment requires 120-125 yearss from transfering to adulthood. The field experiment was conducted during February to May 2004, following different phases of paddy growing from transfering to adulthood ( Table 1 ) .

Table 1: Time and Date of Field Experiment

Date of measuring

Growth Stage

Transplanting

Stooling

Max. Stooling

Max. Blooming

Ripening

DAP ( Day after seting )

7

25

50

90

110

Date

14 Feb. 2004

3 Mar. 2004

28 Mar. 2004

7 May 2004

27 May 2004

Field Measurement

Above-ground Biomass of Rice, CH4 Emission Rate, Spectral Reflectance Measurement,

Dirt Factors Data ( Soil Temp. , Soil Eh, Soil pH )

Six experimental sites were chosen in six small towns with mean interdistance of about 30 kilometers between sites. The day of the months of rice transplantation are the same among the six sites. Field information from each site during each growing phase were collected on the same twenty-four hours. In each site, a closed chamber with four equal size of boxes ( 30 x 30 ten 30 cm each ) was setup for mensurating methane gas emanation during 10 am to 1 autopsy. During this clip, the sum of methane gas emanation was collected 5 times at an equal interval of 5 proceedingss ( 0, 5, 10, 15, 20 minute ) for analyzing methane gas emanation rate. Then, 20 samples were collected per site per twenty-four hours per phase. There were 120 samples per phase of rice growing. A sum of 600 methane concentration samples were collected from 5 phases right from transfering to adulthood phase ( Table 2 ) .

Table 2. Phases of paddy cultivation and sample aggregations

Phase

Phase of growing

Time rhythm of methane

gas emanation informations

( 5 samples at an interval

of 5 minute in each phase )

No. of sites

4 closed Chamberss each site

Entire samples

1

2

3

4

5

6

1

Transplanting

5 samples

20

20

20

20

20

20

120

2

Stooling

5 samples

20

20

20

20

20

20

120

3

Maximal tillering

5 samples

20

20

20

20

20

20

120

4

Maximal blossoming

5 samples

20

20

20

20

20

20

120

5

Ripening or Maturity

5 samples

20

20

20

20

20

20

120

Entire sample size

100

100

100

100

100

100

600

Note: 4 closed Chamberss x 5 times ten 6 sites = 120 samples in each phase of paddy growing

Table 1. Phases of paddy cultivation and sample aggregations.

Phase

Phase of growing

Time rhythm of methane

gas emanation informations

No. of sites

Entire samples

1

2

3

4

5

6

Phase 1

Transplanting

5 samples at an

interval of 5 proceedingss

in each phase

120

Phase 2

Stooling

4 Chamberss each site

120

Phase 3

Maximal tillering

120

Phase 4

Maximal blossoming

120

Phase 5

Ripening or Maturity

120

Entire sample size

600

Note: 4 closed Chamberss x 5 times ten 6 sites = 120 samples in each phase of paddy growing

In add-on to this, gas was collected outside the closed chamber in a syringe of sum 30 milliliter per site per phase stand foring the CH4 existed in the ambient air. A sum of 30 gas samples were collected for comparing with the methane gas samples collected through gas Chamberss.

Methane gas emanation analysis

For methane gas emanation analysis, gas chromatography ( Shimadzu GC-12A ) equipped with a Flame Ionization Detector ( FID ) was used and followed by International Atomic Energy Agency ( IAEA ) for each appraisal ( IAAE 1992 ) . Methane gas emanation rate was calculated from the measured concentration inside the Chamberss as follows ( Quiamco 1996 ) ;

Where:

E = methane gas emanation rate/uptake ; mg CH4 m-2 h-1

dc/dt = alteration of gas concentration ; ppm h-1

H = effectual tallness of chamber ; m

Mw = molecular weight of methane gas = 16.123 x 103 milligram

Mv = molecular volume of methane gas = 22.41 ten 10-3 M3

Tst = standard temperature = 273.2 & A ; deg ; K

T = temperature ; & A ; deg ; C

Base on the above theoretical account, 600 methane concentration samples collected in 4 gas Chamberss from six sites over five phases were used to set up methane gas emanation rate, which eventually yielded 120 ( 4x6x5 ) observations.

4.2. Auxiliary measurings

Above-ground biomass of rice, dirt factors ( dirt temperature, dirt oxidation-reduction potency ( Eh ) and dirt pH at 5 cm deepness of top dirt utilizing a battery operated metre ) were measured at six sites ( Mitra et al. 2002 ; Huang et al.1997 ) . They were measured 4 times in each phase of paddy growing. A sum of 120 samples of above-ground biomass of rice were collected and 120 samples of each dirt factors ( dirt temperature, dirt oxidation-reduction potency and dirt pH ) were measured. These informations were analyzed to correlate with methane gas emanation rate. Statistical analysis of experimental information was accomplished utilizing Microsoft Excel and SPSS 12.0 statistical programme.

4.3. Spectral coefficient of reflection measuring

Spectral coefficient of reflection was measured 4 times in each site in each phase of paddy growing, which generated 120 samples. Spectral glow from the incident solar radiation and vegetive screen were acquired under the same Sun conditions to cipher coefficient of reflection spectra of paddy sporadically during the turning periods of 2004. The coefficient of reflection of single wavelength was calculated by spliting the flora glow measurings with the corresponding incident solar radiation measurings. A portable spectrometer was used for the land measurings. Measurements were made at each secret plan utilizing sunlight as light beginning on clear or close cloudless yearss between 10 am to 1 autopsies local standard clip. Coefficient of reflection spectra were measured above the canopy utilizing a high spectral declaration spectrometer, in the scope 675 – 750 nanometre. To mensurate glow of the canopy, the spectrometer was attached to a telescope with a field of position ( FOV ) of 10 & A ; deg ; , which was positioned above the canopy at a tallness of about 1 metre. Measurements of glow were repeated at least five times at each trying station and the mean value was used in the analysis ( Yang and Su 1998 ) .

The NDVI was defined as ( NIR-RED ) / ( NIR+RED ) ( Van Niel and Tim 2001 ) . Three hundred observations of coefficient of reflection of the wavelengths at RED ( 675 nanometre ) and NIR ( 750 nanometre ) measured from spectrometer were selected and used for analysis. Regression analysis was performed to suit curves in order to set up relationship between NDVI and methane gas emanation, and above-ground biomass of rice.

4.4. Model development

The experimental datasets observed from 6 sites were used to suit and prove theoretical accounts by set uping the relationship between methane gas emanation rate, above-ground biomass of rice and spectral coefficient of reflection of rice works from field measuring to develop the empirical theoretical account. An exponential equation is used to depict those relationships. Then, model standardization and proof utilizing the ascertained values from land informations measuring compared with the estimated values is obtained from empirical theoretical account.

4.5. Accuracy of methane gas emanation appraisal

The estimated consequences of above-ground biomass of Paddy, norm of methane emanation rates including accumulative methane emanation were verified for their truth. To mensurate how good of the appraisal to suit the land informations, two statistical indexs are selected to find. They are the comparative mistake and coefficient of finding.

The Relative Error and Coefficient of Determination are summarized in expression:

Relative Error = 100* [ { Sum ( Estimation-ground ) 2 } / { Sum ( Ground2 ) } ] 0.5

Coefficient of Determination = ( Explained Variation ) / ( Entire Variation )

Consequences

5.1. Methane gas emanation rate

To gauge methane gas emanation, the measurement clip was set in relation to different phases of paddy growing distributing over five phases such as transfering phase, stooling phase, maximal tillering phase, maximal blossoming phase and maturation phase ( adulthood phase ) . The field measuring informations presented in Figure 2 explains the important emanation, which was observed in irrigated Paddy Fieldss. The methane gas emanation rate was bit by bit increased from transfering phase to maximum flowering phase. It was highest emitted during maximal flowering phase ( 90 yearss after seting ) . After that, the rate of methane gas emanation was decreased in the maturation phase. The coefficient of fluctuation is 51.28 % . In Figure 2 ( a ) , the comparing between the methane gas emanation rate and Day After Planting ( DAP ) shows that the methane gas emanation rate is positively correlated with the twenty-four hours after seting ( R2=0.81 ) . This consequence was in good understanding with the findings of Kanchanasutorn, ( 1993 ) and Chareonsilp et al. , ( 1996 ) and Xunhua et al. , ( 1997 ) . It is observed that the methane gas emanation rate additions following the growing phases of rice works. It is highest in maximal flowering phase of rice works and lessenings in maturing or adulthood phase. It is besides farther tried to utilize mean rate of methane gas emanation to understand the relationship with twenty-four hours after seting, of which the consequence is presented in Figure 2 ( B ) . In this instance the coefficient of relationship is higher that explains R2 equal to 1.

Figure 2 ( a ) . A comparing between methane gas emanation rate and Day After Planting ( DAP ) .

Figure 2 ( B ) . A comparing between mean methane gas emanation rate and Day After Planting ( DAP ) .

5.2 Relationship between above-ground biomass and twenty-four hours after seting

Figure 3 ( a ) presents the relationship between above-ground biomass of Paddy and twenty-four hours after seting utilizing 120 observations. The above-ground biomass is really good correlated with the twenty-four hours after seting ( R2 = 0.94 ) , analyzed from five phases of paddy growing ( transfering, stooling, maximal tillering, maximal blossoming and maturing phase ) . It indicates that the above-ground biomass is highest at maximal flowering phase ( 90 yearss after seting ) . The above-ground biomass bit by bit increases from transfering phase to maximum flowering phase. The periods from transfering phase to maximum tillering is the vegetive stage when rice workss produce root and leave. Subsequently, the growing of rice enters to panicle phase, booting phase and flowering phase with increasing order of the above-ground biomass of rice works. After that, sum of the above-ground biomass lessenings due to drying of leave and decrease of seed wet. The coefficient of fluctuation is equal 66.45 % . Similarly, the mean values of above-ground biomass informations are presented in Figure 3 ( B ) . This shows that the mean above-ground biomass is extremely correlated with the twenty-four hours after seting excessively ( R2 = 1 ) .

Figure 3 ( a ) Above-ground biomass of rice and Day

After Planting.

Figure 3 ( B ) Average above-ground biomass of rice and

Day After Planting.

5.3 Relationship between methane gas emanation rate and above-ground biomass

Figure 4 ( a ) shows the relationship between methane gas emanation rate and above-ground biomass of rice from the land measuring. The above-ground biomass of rice is positively correlated with the methane gas emanation rate ( R2 = 0.79 ) . The mean values of six phases are besides used to compare with the ascertained informations. Figure 4 ( B ) shows the mean methane gas emanation rate and mean above-ground biomass of rice is good correlated ( R2 = 0.80 ) . This is really similar in both instances.

Figure 4 ( a ) Methane gas emanation rate and above-

land biomass of rice.

Figure 4 ( B ) Average methane gas emanation rate and

mean above-ground biomass of rice.

5.4 Relationship between methane gas emanation rate and dirt factors informations

Figures 5 ( a and B ) , 6 ( a and B ) and 7 ( a and B ) show the relationship between methane gas emanation rate and dirt factors informations ( dirt temperature, dirt oxidation-reduction potency and dirt pH ) .

Figure 5 ( a ) Methane gas emanation rate and dirt

temperature

Figure 5 ( B ) Average methane gas emanation rate and

mean dirt temperature

From Figure 5 ( a ) , it is observed that rice grown under the temperature of flooded dirts scopes from 24oc to 33oc. Variations in methane gas emanation rate has been correlated with dirt temperature utilizing 120 samples. It is found that methane gas formation reaches a maximal temperature of 31oc in this experiment. The rate of methane formation was really small below 28oc. Soil temperature on the methane flux with doubling of emanation rates when temperature increases from 28oc to 32oc like the observation of Wassman and others ( Wassman et al.1998 ) . The relationship between methane gas emanation and dirt temperature is ill observed. The methane gas emanation rate is positively correlated with dirt temperature with low value ( R2 = 0.27 ) . It is possible that the addition in soil temperature stimulates microbic activities in dirt, particularly under the flooding status, and therefore leads to higher methane emanation rate ( Khaili and Rasmussen, 1991 ; Holzapfel-Pschon et al.1986 ) and Yamane and Sato, 1967 ) . And from Figure 5 ( B ) , presents the relationship between the norm of methane gas emanation and mean dirt temperature. In this survey, the relationship is instead good established correlated ( R2 = 0.72 ) .

Figure 6 ( a ) Methane gas emanation rate and dirt Rh

Figure 6 ( B ) Average methane gas emanation rate and

mean dirt Rh

In Figure 6 ( a ) , 120 samples of dirt oxidation-reduction potency has been correlated with 120 observations of methane gas emanation rate. The dirt redox potency for induction of methane gas emanation production is about -100 to -150 millivolt. And the dirt redox potency for maximising methane gas emanation production was about -250 millivolt. The relationship of methane gas emanation rate and dirt redox possible becomes negatively exponential ( R2 = 0.35 ) . Takai et Al. ( 1956 ) demonstrated that the redox potency of dirts must be below -200 millivolt to bring forth CH4. ALGAS concluded that methanogenic bacteriums can merely work at redox possible degrees below -200 millivolt and that a correlativity exists between methane emanation and dirt redox possible. Like the survey in methane emanations from a rice field in relation to dirty oxidation-reduction and microbiological procedures of Hou and others, it shows that emanation of methane is strongly correlated with altering in dirt oxidation-reduction potency ( Hou et al 2000 ) . Yagi and Minami reported that redox possible values varied from -100 to -200 millivolt for the induction of methane production in Paddy dirts ( Yagi and Minami 1990 ) . Methane gas emanation rate was highest when redox potency was lowest. Harmonizing to Conrad ( 1989 ) reported that methane is generated by methanogenic bacteriums under anaerobiotic dirt conditions at low oxidation-reduction potencies, lower than -200 millivolt. Figure 6 ( B ) presents the relationship between the norm of methane gas emanation and mean redox potency, which is good correlated ( R2 = 0.94 ) .

Figure 7 ( a ) Methane gas emanation rate and dirt pH

Figure 7 ( B ) Average methane gas emanation rate and

mean dirt pH

Figure 7 ( a ) shows that the relationship between 120 observations of methane gas emanation rate and 120 samples of dirt pH is found hapless ( R2 = 0.36 ) . The methane gas formation is merely efficient in a narrow pH scope around neutrality ( pH from 6.20 to 6.95 ) . Methane gas emanation rate has non increased so much at a pH of 6.20 -6.80 and it increased bit by bit at a pH of 6.80-6.95. The increase of methane gas emanation rate was evidently increased at a pH closed to impersonal. It is found that highest methane production rate occurred at a pH of 6.90 to 6.95 in an acidic dirt. This is because the methanogenic bacteriums prefer the impersonal pH for their growing. It is by and large recognized that methane formation is merely efficient in a narrow pH scope around neutrality with pH value from 6.4-7.8 ( Intergovernmental Panel on Climate Change 1996 ) . The consequence of implosion therapy is to increase the pH in acerb dirt, while it decreases the pH in alkalic dirt. The addition of pH in acid dirts is chiefly due to the decrease of acidic Fe3+ to Fe2+ which at the same time reduces the redox potency. Most methanogens are neutrophilic with a comparatively narrow pH scope of 6-8 ; the optimum being 7 ( Oremland 1988 ; Alexander 1977 ) . Wang et Al ( 1993 ) found highest CH4 production rates at a pH of 6.9 to 7.1 in an acidic dirt. Figure 7 ( B ) presents the relationship between the mean methane gas emanation rate and mean dirt pH, which is besides good correlated ( R2 = 0.86 ) .

5.5 Relationship between methane gas emanation rate and NDVI

Another empirical theoretical account is established by analysing the relationships between land measuring of methane gas emanation rate and NDVI. Figures 8 ( a, B, degree Celsius, vitamin D, vitamin E, degree Fahrenheit and g ) shows the relationship between methane gas emanation rate from land measuring with NDVI in each phase individually, and besides state of affairs of all phases of paddy growing taken together, and eventually the mean state of affairs of all phases.

Figure 8 ( a ) Relationship between methane gas emanation

rate with NDVI at transfering phase

Figure 8 ( B ) Relationship between methane gas

emanation rate with NDVI at stooling phase

Figure 8 ( degree Celsius ) Relationship between methane gas emanation

rate with NDVI at soap. tillering phase

Figure 8 ( vitamin D ) Relationship between methane gas emanation

rate with NDVI at soap. blossoming phase

Figure 8 ( vitamin E ) Relationship between methane gas emanation

rate with NDVI at maturing phase

Figure 8 ( degree Fahrenheit ) Relationship between methane gas emanation

rate with NDVI in all growing phases

Figure 8 ( g ) Relationship between methane gas emanation

rate with NDVI in mean state of affairs of all

growing phases

Figure 8 ( a ) shows the relationship between methane gas emanation rate with NDVI at transfering phase are ill correlated ( R2 = 0.46 ) ( Twenty four samples of spectral coefficient of reflection of rice from 6 sites were collected from each phase of paddy growing has been correlated with methane gas emanation rate ) . At this first phase of paddy growing ( transfering phase ) , NDVI value was non much high ( 0.21 – 0.23 ) because the sum of rice that covered the Paddy filed was excessively low that affected the methane gas emanation rate.

Figure 8 ( B ) and 8 ( degree Celsius ) show the relationship between methane gas emanation rate with NDVI at stooling phase and maximal tillering with just understanding ( R2 = 0.55 and 0.59 ) . It may be caused by the sum of rice that covered the Paddy filed was increasing. The value of NDVI ranged between 0.30 – 0.70. In add-on, the methane gas emanation rate was higher than first phase ( 15 – 30 mg/m2/day ) . And in the maximal tillering phase, value of NDVI ranged between 0.65-0.90. The sum of Paddy covered all paddy Fieldss and the methane gas emanation rate was higher than two old phases.

Figure 8 ( vitamin D ) shows the relationship between norm of methane gas emanation rate with NDVI at maximal flowering phase with hapless understanding ( R2 = 0.34 ) . The hapless understanding may be caused by H2O, dirt wet content, weather forecasting and cloud status that affect the spectrometer measuring. The value of NDVI ranged between 0.72 – 0.85 and the methane gas emanation rate was highest ( 50 – 75 mg/m2/day ) .

Figure 8 ( vitamin E ) shows the relationship between norm of methane gas emanation rate with NDVI at maturing phase, which is instead reasonably correlated ( R2 = 0.60 ) . The value of NDVI ranges between 0.74 – 0.81 and the methane gas emanation rate was dropped to 30-50 mg/m2/day. In this phase, the Paddy turns to adulthood with dried foliages, decrease of seed wet and ready to reap.

Figure 8 ( degree Fahrenheit ) shows the relationship between methane gas emanation rate and NDVI at all growing stages taken together. The relationship between methane gas emanation rate is positively correlated with NDVI ( R2 = 0.56 ) . Figure 8 ( g ) presents the relationship between the norm of methane gas emanation and mean NDVI in 5 growing phases, which is good correlated ( R2 = 0.79 ) .

5.6 Relationship between above-ground biomass of rice and NDVI

Figure 9 ( a ) Above-ground biomass of rice and NDVI

Figure 9 ( B ) Average above-ground biomass of rice and

mean NDVI

From Figure 9 ( a ) , the empirical theoretical account for gauging above-ground biomass of rice has been established by analysing relationships between 120 observations of above-ground biomass of rice and NDVI. The relationship between above-ground biomass rice and NDVI is strongly positive. The above-ground biomass of rice is positively correlated with NDVI ( R2 = 0.82 ) . The NDVI value in this phase is 0.2 – 0.85. When land gets covered with heavy flora, the NDVI value becomes high. NDVI provides a rough estimation of flora wellness and a agency of monitoring alterations in flora over clip. The possible scope of values is between -1 and 1, but the typical scope is between about -0.1 ( NIR less than VIS for a non really green country ) to 0.7 ( for a really green country ) . And from Figure 9 ( B ) , the relationship between the norm of above-ground biomass of rice and mean NDVI is good correlated. The correlativity coefficient is instead high ( R2 = 0.92 ) .

5.7 Accuracy of methane gas emanation appraisal

Accuracy of methane gas emanation appraisal is eventually done. The estimated consequences of above-ground biomass of rice, norm of methane emanation rate including accumulative methane gas emanation were verified for truth. The comparative mistake of the appraisal of above-ground biomass of rice, methane gas emanation rate and accumulative methane gas emanation derived by empirical theoretical account is 16.50, 15.19 and 11.26 % severally ( or the truth is 83.50, 84.81 and 88.74 % ) . And the coefficient of finding of them is 0.91, 0.93 and 0.99 severally.

6. Decision

To gauge methane gas emanation from irrigated Paddy Fieldss, mold is utile. However, the truth of appraisal depends on many act uponing factors during cultivation period.

Empirical theoretical account for gauging methane gas emanation from irrigated paddy field, by utilizing information extracted from distant feeling methodological analysis ( spectrometer measuring ) has been developed in this survey. It has been found that distant feeling technique provided the utile information for gauging methane gas emanation every bit good as for appraisal of above-ground biomass of rice. The truth of appraisal and relationships between estimated consequences and land informations are satisfactory as R2 value is more than 0.91 with less than 16.50 % of comparative mistake.

Benefit of utilizing spectrometer was more homogenous in object sensing with more sets of wavelengths. Therefore, the estimated consequences are more accurate and more practical in calculation. Furthermore, it is really cost effectual in utilizing spectrometer, which provides periodical acquisition of informations everyday. Therefore, as spectrometer gives high truth in appraisal, it is strongly recommended for utilizing distant feeling informations because of its cheaper cost twenty-four hours by twenty-four hours and more often acquisition of periodical informations. The consequence has been found that distant feeling informations provide utile information for designation of paddy field countries every bit good as for appraisal of methane gas emanation and biomass of Paddy. This provides uninterrupted chance in supervising methane gas emanation from paddy Fieldss covering a big country. However, cloud status affects the spectrometer measuring. During the fallow period, and organ transplant phase, it is the restriction of the distant detection technique to observe any biomass of paddy Fieldss. Hence, it is non desirable to utilize NDVI in the early phase of works growing. This affects the appraisal of biomass by utilizing RS biomass theoretical account, which accordingly influence the consequence of methane gas emanation rate of appraisal. The truth of appraisal depends on many act uponing factors during the cultivation period as mentioned above.

The methodological analysis proposed here is based on the survey in irrigated Paddy Fieldss under acidic dirt assorted with ash from burned rice straw. Further surveies are recommended in other locations with different cultivation patterns ( both irrigated and non-irrigated state of affairs ) to do the all right tuning of this theoretical account.

Recently, much work has been done on methane gas emanation appraisal from paddy Fieldss. All of them instead worked on field measuring method and techniques. Some of the research workers ( Eiumnoh and Yaianong 2001 ) studied methane gas emanation appraisal from paddy Fieldss by utilizing application of distant feeling in Central Plain of Thailand. Their survey was intended to develop a mathematical theoretical account to gauge methane gas emanation from deep-water paddy field by utilizing Landsat and NOAA image informations using distant feeling techniques. That theoretical account was compared with the existent field measuring at the Rice Research Center in Prachinburi. Appraisal on methane appraisal was done by Tamura and Yasuoka ( 1995 ) in western Siberian Wetlands by utilizing distant feeling techniques. They investigated the flora screen by utilizing distant feeling techniques and estimated regional methane emanations by uniting the consequences of satellite observations with land methane measurings. They analyzed a SPOT/HRV image at Plotnikovo trial site in west Siberia to sort wetland ecosystems. Methane emanation from the image was estimated by uniting the consequence of emanation estimations with those obtained from airborne methane measurings. Takeuchi, Tamura and Yasuoka ( 2000 ) studied on the appraisal of the methane emanation from west Siberian wetland by scaling between NOAA/AVHRR and SPOT/HRV informations. They investigated the land screen conditions in western Siberian wetlands by utilizing distant feeling techniques and estimated methane emanation in broad country by uniting the consequences of satellite observation with land methane measurings. Furthermore, Takeuchi, Tamura and Yasuoka ( 2001 ) developed a grading technique to generalize the local information on land screen type combination from high spacial declaration informations ( OPS ) to more extended country through low spacial declaration informations ( AVHRR ) with broad coverage. Paddy field country was extracted from OPS informations. AVHRR NDVI was statistically regressed with the matching paddy country ratio from OPS pels for matching AVHRR pel. With this arrested development theoretical account ( scaling theoretical account ) , local information of the paddy country was estimated merely from AVHRR informations over extended country outside the OPS information. And this method is applied to the paddy field extraction in the Central Plain of Thailand. Then, they estimated the methane emanation from paddy Fieldss by multiplying observed in situ methane flux and the entire paddy country estimated in whole AVHRR.

For the orbiter informations such are the MODIS, NOAA/AVHRR, LANDSAT, IRS and IKONOS informations may be tried afterwards to compare the consequences for all right tuning of the theoretical account. However this is non considered really appropriate at present as spectrometer gives a high preciseness degree of ascertained informations at the local degree because rice Fieldss in Thailand are non really big and besides assorted with other vegetive screen. So it is hard to separate the paddy country from other land usage types with MODIS and NOAA/AVHRR informations. They are designed to supply measurings in large-scale planetary kineticss. The spacial declaration of MODIS is composed of 250 metre ( bands 1-2 ) , 500 metre ( bands 3-7 ) and 1,000 metre ( bands 8-36 ) . Spatial declaration of NOAA/AVHRR information is more than 1 kilometer.

In instance of LANDSAT 7 and IRS information with 30 and 23.5 metre declaration severally are besides hard to sort the paddy country from other land usage types. For IKONOS informations with 4 metre declaration is instead easy to sort the paddy country from other land usage types. However, it requires a batch of scene imagination to fix mosaic for the whole survey country as one scene imagination covers merely 11.3 ten 11.3 sq kilometer of country. Besides, the revisited day of the months of orbiters are non the same with the day of the month of experiments precisely.

In this research, spectrometer measuring technique has been used in topographic point of satellite imagination for proving and formalizing the truth. In making so, this technique contributes for gauging methane gas emanation on a regional graduated table. There forward, this methodological analysis is proved to be sound and considered more dependable for application non merely in Thailand but in other paddy turning states.

Recognitions

The work was performed with the grant supported by Srinakharintrwirot University, Thailand. The writers wish to thank all laboratory staffs in the Prachin Buri Rice Research Center for widening their support and cooperation in informations analysis. The writers are really much grateful to anon. referees for their valuable suggestions to better the quality of this paper.