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

Abstract

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.

Diurnal Methane Fluxes as Affected by Cultivar from Direct-Seeded, Delayed-Flood Rice Production

“…These results were similar to the measured diurnal variations reported previously [2] [4] [6]- [13]. Though greater diurnal variations have been reported early compared to late in the growing season [8] [10], results of this study indicated the proportional range in diurnal CH 4 fluxes/estimated emissions was similar before and after heading from both soil textures (Table 3). The numeric peak CH 4 flux was 23% to 33% greater than the numeric low among the various measurement times of day across the four location-growth stage combinations, which was similar to the magnitude of variation reported by Yagi and Minami [13].…”

“…However, numerous studies have also reported no significant difference in CH 4 emissions between day and night [6] [14] [15]. Differences between cultivars have generally been consistent given the multitude of factors that have been shown to affect CH 4 fluxes and emissions throughout a growing season, such as soil texture [16] [17] [18] [19], fertilizer nutrient source [20], organic soil amendments [8] [12], residue management/previous crop [21] [22] [23] [24], water management scheme [8] [25] [26], and production system [27]. Typically, hybrid rice cultivars have lower season-long CH 4 emissions than do pure-line cultivars [23] [24] [28] [29].…”

“…Most studies have reported peak emissions during the daytime, either in late morning to early afternoon [6] [7] [8] [9] or during mid-to late afternoon [2] [4] [7] [10] [11] [12] [13]. During the night and early morning have generally been reported as the times of day with the lowest CH 4 fluxes/emissions [6] [7] [8] [11] [13]. Previous reports indicate diurnal variations (i.e., the amplitude and timing of flux minima and maxima) in CH 4 emissions may also differ over time within the growing season [8] [10] [12].…”

“…During the night and early morning have generally been reported as the times of day with the lowest CH 4 fluxes/emissions [6] [7] [8] [11] [13]. Previous reports indicate diurnal variations (i.e., the amplitude and timing of flux minima and maxima) in CH 4 emissions may also differ over time within the growing season [8] [10] [12]. However, numerous studies have also reported no significant difference in CH 4 emissions between day and night [6] [14] [15].…”

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

“…Methane emissions are stimulated by organic amendments (Watanabe et al, 1995;Bronson et al, 1997), but this effect may be due partly to lower CH 4 oxidation caused by more rapid heterotrophic 0 2 consumption at the soil surface.…”