Appropriate frequency and time of day to measure methane emissions from an irrigated rice paddy in Japan using the manual closed chamber method
MetadataShow full item record
Minamikawa K, Yagi K, Tokida T, Sander BO, Wassmann R. 2012. Appropriate frequency and time of day to measure methane emissions from an irrigated rice paddy in Japan using the manual closed chamber method. Greenhouse Gas Measurement and Management 2(2-3):118-128
Permanent link to this item: http://hdl.handle.net/10568/42017
Rice agriculture is a large anthropogenic source of atmospheric methane (CH 4 ). The reliable estimation of CH 4 emissions requires frequent measurements to trace diurnal and seasonal variations. To evaluate the appropriate intervals and optimal time of day to measure CH 4 emissions using the manual closed chamber method, this study analysed four datasets of CH 4 fluxes in a Japanese irrigated rice paddy measured at 2-hour intervals using the automated closed chamber method. The typical diurnal variation in the CH 4 flux was observed after the rice's heading stage, during which the daily time-weighted mean CH 4 flux was observed twice, in the 08:00 11:59 and 18:00 21:59 time windows. During the flooded rice-growing period, the CH 4 emissions, which were estimated by weekly measurements once per day during the 10:00 11:59 time window, corresponded to 93 106% of the emissions calculated using the automated measurement method. In contrast, no regular measurement strategies produced a satisfactory estimate of the CH 4 emissions during the non-flooded rice-growing period because of a sharp increase in the CH 4 flux just after the drainage. Consequently, the combination of weekly measurements once per day at approximately 10:00 as local mean time for the flooded rice-growing period and daily measurements once per day during the daytime for 1 week after each drainage event is recommended as a strategy to obtain the estimation with a ±10% error.