TUNABLE DIODE-LASER MEASUREMENTS OF METHANE FLUXES FROM AN IRRIGATED RICE PADDY FIELD IN THE PHILIPPINES

This paper presents the first micrometeorological-based measurements o f methane (CH4) emissions from Asian rice paddies of which we are awar e. The research features the tunable diode laser trace gas analyzer sy stem (TGAS) recently developed at the University of Guelph. CH4 fluxes were measured between March 9 and 24, 1992, from an irrigated rice pa ddy field at the International Rice Research Institute (IRRI), the Phi lippines. The daytime CH4 flux averaged 6.0 mu g m(-2) s(-1). The CH4 fluxes s displayed a diurnal trend similar to daily soil temperature c urves, with peak emissions of about 8 mu g m(-2) s(-1) in the early af ternoon. A tenfold increase in CH4 emissions (to s about 70 mu g m(-2) s(-1)) during a brief weeding experiment resulted from soil disturban ce. Up to 25 mu g m(-2) s(-1) of CH4 were released during a drying of the field, s after which unsuitable soil redox potentials apparently s uppressed methanogenesis. The CH4 flux was also arrested when the fiel d was flooded with oxygen-rich water during a heavy rainstorm.