Methane emission from deepwater rice fields in Thailand

Field experiments were conducted in the Prachinburi Rice Research Center (T hailand) from 1994 to 1998. The major objective was to study methane (CH4) emission from deepwater rice as affected by different crop management. Irri gated rice was investigated in adjacent plots, mainly for comparison purpos es. The 4-yr average in CH4 emission from deepwater rice with straw ash (bu rned straw) treatment was 46 mg m(-2)d(-1) and total emission was 98 kg ha( -1) yr(-1). For irrigated rice, the average emission rate and total emissio n for the straw ash treatment was 79 mg m(-2) d(-)1 and 74 kg ha(-1) yr(-1) , respectively. Low emission rates may partially be related to acid sulfate soil of the experimental site. Without organic amendment, the seasonal pat tern of CH4 emission from deepwater rice was correlated with an increase in biomass of rice plants. Emission rates from deepwater rice depend on the p roduction of biomass and the straw management as well. Methane emission was greatest with straw incorporation, followed by straw compost incorporation , zero-tillage with straw mulching, and least with straw ash incorporation. The seasonal pattern of CH4 ebullition in deepwater rice was consistent wi th seasonal emission, and total ebullition corresponded to 50% of total emi ssion. Dissolved CH4 concentrations in the surface soil (0-5 cm) were simil ar to those in the subsoil (5-15 cm), and the seasonal fluctuation of disso lved CH4 was also consistent with the seasonal CH4 emission. Increase in pl ant density and biomass of irrigated rice grown by pregerminated seed broad casting enhanced CH4 emission as compared with transplanting.