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

Abstract

An investigation was carried out to quantify the present fluxes of CH₄ and CO₂ from 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 50°C 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.

Key Words: Methane and carbon dioxide flux; Rice field; Environmental controls; Organic analysis

DOI: http://dx.doi.org/10.3329/jesnr.v4i2.10123

J. Environ. Sci. & Natural Resources, 4(2): 1-6, 2011