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Methane and Carbon Dioxide Flux from Rice Field: Contribution of Environmental Controls

M. B. Khan
School of Earth, Atmospheric and Environmental Science, University of Manchester, UK

S. Boult
School of Earth, Atmospheric and Environmental Science, University of Manchester, UK

P. Duy
School of Earth, Atmospheric and Environmental Science, University of Manchester, UK

E. Sharmin
Department of Environmental Science, Bangladesh Agricultural University, Mymensingh

M. A. Baten
Department of Environmental Science, Bangladesh Agricultural University, Mymensingh

Abstract/ Executive Summary:

An investigation was carried out to quantify the present fluxes of CH₄ and CO₂from rice soils and also to investigate the controls on gas production. Soil samples were collected from rice field at Mymensingh, Bangladesh to characterize the samples and for ex-situ measurement. Water content was determined by drying to constant weight at 50⁰C from rice soils. To determine the organic compound present in rice soil, normal pyrolysis was done. Gasclam® was used to measure the gas concentration from both ex-situ and in-situ measurement. Ex-situ measurement was conducted to measure the gas fluxes from the soil and which was validated by measuring concentration ratios in-situ. Moreover, in-situ measurement was carried out to investigate the influences of controls of environment on gas production and migration. In ex-situ measurement the production rate of CH4 at shallow and deep rice soil was 0.07 mole/tonne dry weight/day and 0.09 mole/tonne dry weight/day, respectively. On the otherhand, the production rate of CO₂ in shallow and deep borehole was 0.23 mole/tonne dry weight/day and 0.29 mole/tonne dry weight/day, respectively. In in-situ measurement the average production rate of CH₄ in shallow soil was 0.34 % while at deep soil it was very low. The CO₂ concentration at shallow and deep soil was 6.37 % and 24.70 %, respectively. The ex-situ measurements of greenhouse gas fluxes are not reliable enough for rice soil as they are invalidated by comparison with concentration ratios of insitu measurements of greenhouse fluxes. There is no strong relationship between atmospheric pressure and patterns of greenhouse gas production in rice soils. Gas concentrations are remarkably constant despite varying pressure. However, the gas production and atmospheric pressure showed fluctuation during the measurement period. There was not enough organic matter in rice soil for detection organic analysis. However in future the organic matter can be extracted and analysed.

Keywords: Methane and carbon dioxide flux, Rice field, Environmental controls, Organic analysis

Location: Agriculture Farm of Bangladesh Agricultural University

Start Date: 13-01-2010

End Date: 13-05-2010

Program Area: Risk Management in Agriculture

Commodity: Rice

Objectives:

1.To quantify greenhouse gas fluxes from rice soils through both insitu and ex-situ measurement, and 2. To improve understanding of the process controlling gas production in soil in order to predict how greenhouse gas fluxes and composition may change in the future.

Methodology:

The research area is situated at the rice field of Agriculture Farm of Bangladesh Agricultural University (24.75° N, 90.5° E, and 18 meters above sea level) which is located to the 6 km south of Mymensingh town. The GasClam was installed at Boro rice field. The Boro rice was planted on 13 January, 2010 and it was harvested on 13 May, 2010. Soil samples were taken from Boro rice field at four different times from both 0-40 cm and 40-100 cm soil depths for ex-situ measurement. Water content was determined by drying to constant weight at 50⁰C from rice soils. Eight samples were taken from rice soil to measure the water content of the samples. Two samples were taken from the early vegetative stage and other two were taken from late vegetative stage of rice to show the change of organic compounds especially humic acid (phenol) and polysaccharides (primary and secondary polysaccharides) between these two stages. Pyrolysis was performed at 700⁰C by CDS 5200 pyroprobe unit (Analytical Inc., Pyroprobe 5000 series), fitted with an platinum coil interfaced to an 7890A gas chromatograph (Agilent Technologies) coupled to a 5975C MSD (Agilent Technologies) mass spectrometer operated in electron ionization (EI) mode (scanning a range from m/z 50- 600 at 2.7 scan s^-1, ionisation energy 40 eV). For exsitu measurement of the soil, the collected soil samples were kept into a special glass bottle and 5 NaOH pellet were put in each bottle, then cap was tighten. For anaerobic measurement, the bottle was purged with nitrogen and kept in incubated condition while for aerobic measurement the bottle was kept in incubated condition without purged with nitrogen. After 7 days the changes of pressure was measured from the bottle of soil sample through oxytops. In anaerobic bottle, an increase in pressure is assumed to be a result of CH₄ production. In aerobic bottles, a decrease in pressure is assumed to be a result of the use of oxygen which is equivalent to CO₂ production. Finally the pressure was converted to mole/ tonne dry weight soil/day. The in-situ measurement was done by using Gasclam. The Gasclams were inserted into boreholes at shallow (0-40 cm) and deep soil (40-100 cm). The data from the Gasclam was retrieved after several weeks. The duration of the measurement was from 1 March to 21 April, 2010.

Source of Information: J. Environ. Sci. & Natural Resources, 4(2): 1-6, 2011; ISSN 1999-7361

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In ex-situ measurement the production rate of CH₄ at shallow and deep rice soil was 0.07 mole/tonne dry weight soil/day and 0.09 mole/tonne dry weight soil/day, respectively. On the otherhand the production rate of CO₂ in shallow and deep borehole was 0.23 mole/tonne dry weight soil/day and 0.29 mole/tonne dry weight soil/day, respectively. In in-situ measurement the average production rate of CH₄in shallow soil was 0.34 % while at deep soil it was very low. The CO₂ concentration at shallow and deep soil was 6.37 % and 24.70 %, respectively. The ex-situ measurements of greenhouse gas fluxes are not reliable enough for rice soil as they are invalidated by comparison with concentration ratios of in-situ measurements of greenhouse fluxes.

Knowledge Management: Journal