Methane flux from Indonesian wetland rice: the effects of water management and rice variety

Abstract

This study was conducted to determine methane emission rates from wetland rice in tropical regions of West Java, Indonesia, and the effect of various irrigation and water management practices and of rice varieties on the emissions. The experiment tested three water management treatments (continuous flooding, intermittent irrigation, and saturated soil conditions) and three rice variety treatments (unplanted, planted with IR-64, and planted with Cisadane rice) using a split-plot experimental design with three replicates. Methane fluxes were observed during the entire growing period three times per day, one day per week, using a static chamber technique. The results of this study revealed that both water management treatments and rice varieties significantly affected diurnal and seasonal variations of methane flux from wetland rice. Rice with continuously flooded irrigation regimes and intermittent irrigation showed that methane fluxes were 1.4 – 1.9 times higher in the afternoon compared to predawn sampling; however, a reverse phenomenon was observed under saturated soil conditions. The diurnal methane flux variations observed in this study were most likely due to an average difference of 5 ° C in soil temperature at 5-cm depth between predawn and afternoon. Water management treatments greatly affected the average daily methane fluxes. In the continuous flooding treatment, the average methane flux of IR-64 was 20 mg/m 2/hr, greater than that of Cisadane variety (14 mg/m 2/hr). The seasonal daily average methane flux of Cisadane variety was greater than that of unplanted plots, which was 9.4 mg/m 2/hr (p = 0.05). In the intermittent irrigation treatment, the methane flux of IR-64 was about equal to that of the Cisadane rice variety (both 8.7 mg/m 2/hr). However, plots planted with IR-64 and Cisadane emitted more methane than unplanted plots (2.9 mg/m 2/hr; p = 0.05). In saturated soil, the seasonal daily average methane flux of IR-64 was 8.2 mg/m 2/hr, greater than that of Cisadane variety (3.2 mg/m 2/hr, and unplanted plots emitted less methane compared to emissions from both the Cisadane and IR-64 varieties (p = 0.05). This study suggests that rice varieties have significantly different capacities for emitting methane to the atmosphere. The seasonal average daily methane flux of both rice varieties with all water management treatments falls in the range between 4 and 20 mg/m 2/hr, Based on these data we estimate that methane emissions from Indonesian wetland rice is on average around 13 mg/m 2/hr. From these data we estimate total methane emission from Indonesian wetland rice to be about 4 Tg/yr (1 Tg = 10 12 g).