Methane Emission from Deepwater Rice Fields in Thailand

Field experiments were conducted in the Prachinburi Rice Research Center (Thailand) from 1994 to 1998. The major objective was to study methane (CH₄) emission from deepwater rice as affected by different crop management. Irrigated rice was investigated in adjacent plots, mainly for comparison purposes. The 4-yr average in CH₄ emission from deepwater rice with straw ash (burned straw) treatment was 46 mg m^–2d^–1 and total emission was 98 kg ha^–1 yr^–1. For irrigated rice, the average emission rate and total emission 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 pattern of CH₄ emission from deepwater rice was correlated with an increase in biomass of rice plants. Emission rates from deepwater rice depend on the production 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 with seasonal emission, and total ebullition corresponded to 50% of total emission. Dissolved CH₄ concentrations in the surface soil (0–5 cm) were similar to those in the subsoil (5–15 cm), and the seasonal fluctuation of dissolved CH₄ was also consistent with the seasonal CH₄ emission. Increase in plant density and biomass of irrigated rice grown by pregerminated seed broadcasting enhanced CH₄ emission as compared with transplanting.