Automated Chamber Measurements of Methane and Nitrous Oxide Flux in a Flooded Rice Soil: I. Residue, Nitrogen, and Water Management
1997
Bronson, K. F. | Neue, H.-U. | Abao, , E. B. | Singh, U.
Methane and N₂O are gases that are several times more radiatively active than CO₂. It is well known that flooded rice (Oryza sativa L.) soils are a globally important source of atmospheric CH₄. Mitigation strategies for CH₄ flux, such as mid-season drainage, might have the opposite effect on N₂O emissions. An automated chamber system at the International Rice Research Institute in the Philippines measured CH₄ and N₂O 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 N₂O-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 CH₄ flux severalfold. Seasonal CH₄ flux with ammonium sulfate (AS) was one-fourth to one-third the flux with urea. During the DS, however, the seasonal N₂O 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 CH₄ flux up to 60%. However, N₂O flux increased sharply during the drainage period at mid-tillering until reflooding, when it dropped back to near zero.
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