Automated Chamber Measurements of Methane and Nitrous Oxide Flux in a Flooded Rice Soil: I. Residue, Nitrogen, and Water Management

Abstract

Abstract Methane and N 2 O are gases that are several times more radiatively active than CO 2 . It is well known that flooded rice ( Oryza sativa L.) soils are a globally important source of atmospheric CH 4 . Mitigation strategies for CH 4 flux, such as mid‐season drainage, might have the opposite effect on N 2 O emissions. An automated chamber system at the International Rice Research Institute in the Philippines measured CH 4 and N 2 O fluxes from flooded rice and fallow rice fields essentially 24 h a day between December 1992 and April 1994. This period included two irrigated dry rice‐growing seasons (DS) and one wet rice‐growing season (WS). Nitrous oxide fluxes were generally barely detectable during the growing seasons, but small peaks (maximum 3.5 mg N 2 O‐N m ‐2 d ‐1 ) appeared after N fertilizer applications. Methane fluxes, on the other hand, were evident throughout the rice‐growing seasons. Organic matter additions as straw (5.5 t ha ‐1 , dry) or green manure (GM; Sesbania rostrata L.; 12 t ha ‐1 , wet) stimulated CH 4 flux severalfold. Seasonal CH 4 flux with ammonium sulfate (AS) was one‐fourth to one‐third the flux with urea. During the DS, however, the seasonal N 2 O flux was 2.5 times higher with AS than with urea. Mid‐season drainage (2‐wk duration) at either mid‐tillering or panicle initiation was very successful in suppressing CH 4 flux up to 60%. However, N 2 O flux increased sharply during the drainage period at mid‐tillering until reflooding, when it dropped back to near zero.