METHANE FLUX FROM INDONESIAN WETLAND RICE - THE EFFECTS OF WATER MANAGEMENT AND RICE VARIETY

This study was conducted to determine methane emission rates from wetl and rice in tropical regions of West Java, Indonesia, and the effect o f various irrigation and water management practices and of rice variet ies on the emissions. The experiment tested three water management tre atments (continuous flooding, intermittent irrigation, and saturated s oil conditions) and three rice variety treatments (unplanted, planted with IR-64, and planted with Cisadane rice) using a split-plot experim ental design with three replicates. Methane fluxes were observed durin g the entire growing period three times per day, one day per week, usi ng a static chamber technique. The results of this study revealed that both water management treatments and rice varieties significantly aff ected diumal and seasonal variations of methane flux from wetland rice . Rice with continuously flooded irrigation regimes and intermittent i rrigation showed that methane fluxes were 1.4 - 1.9 times higher in th e afternoon compared to predawn sampling; however, a reverse phenomeno n was observed under saturated soil conditions. The diumal methane flu x variations observed in this study were most likely due to an average difference of 5 degrees C in soil temperature at 5-cm depth between p redawn and afternoon. Water management treatments greatly affected the average daily methane fluxes. In the continuous flooding treatment, t he 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 methan e flux of Cisadane variety was greater than that of unplanted plots, w hich was 9.4 mg/m(2)/hr (p = 0.05). In the intermittent irrigation tre atment, the methane flux of IR-64 was about equal to that of the Cisad ane 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 varie ty (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). T his study suggests that rice varieties have significantly different ca pacities for emitting methane to the atmosphere. The seasonal average daily methane flux of both rice varieties with all water management tr eatments falls in the range between 4 and 20 mg/m(2)/hr. Based on thes e 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).