Temporal patterns of methane emissions from wetland rice fields treated by different modes of N application

Abstract

Methane emission rates from wetland rice fields were determined in Los Banos (Philippines) using an automatic system that allows continuous measurements over time. Methane emission was monitored in an irrigated Aquandic Epiaqualf planted to rice cultivar IR72. Urea fertilizer was applied using four modes: (1) broadcast 10 days after transplanting, (2) broadcast at transplanting, (3) broadcast and incorporated at final harrowing, and (4) deep placement as sulfur-coated granules. The treatments were laid out in a randomized complete block design with four replicates. Measurements were done in the 1991 wet season, 1992 dry season (four treatments), and the 1992 wet season (only treatment 3). Methane emission rates from the experimental plots showed pronounced seasonal and diel variations. The diel pattern of methane emission rates followed a consistent pattern, with highest rates observed in the early afternoon and lowest rates in the early morning. Methane emission rate was generally hig hest at the ripening stage. The average methane emission rate during the 1992 dry season (190 mg CH4 m(-2) d(-1)) exceeded the average flux rates of the 1992 wet season (79 mg CH4 m(-2) d(- 1)) by a factor of 2.4. The total methane emitted from these flooded rice fields amounted to 19 g CH4 m(-2) in the dry season with rice yields of 5.2-6.3 t ha(-1) and 7 g CH4 m(-2) in the wet season with rice yields of 2.4-3.3 t ha(-1) regardless of the mode of N application. Significant amounts corresponding to 20 per cent of the methane released under waterlogged conditions were released when the soil was drained after harvest. Emission rates increased sharply when the floodwater receded and macropores started to drain. Emission of methane stopped only when the soil became fully aerated

Sensitivity of wetland methane emissions to model assumptions: application and model testing against site observations

“…The sudden increase in simulated methane emissions immediately after drainage can be attributed to the release of methane previously trapped in the soil and water. This flush of methane has also been demonstrated in other studies (Jain et al, 2000;Wassmann et al, 1994). On a growing-season mean basis, the model performed relatively well for sites with observed mean fluxes less than 200 mg CH 4 m −2 d −1 , and less well for sites with greater than a mean of 200 mg CH 4 m −2 d −1 (Fig.…”

Relationships between methane emissions and soil microorganisms in a double-rice field in southern subtropical China

“…A similar seasonal pattern of methane emissions with the two microbial indexes was observed, this also proved the important role of rice plant growth for seasonal transportation of methane to the atmosphere. This seasonal emission pattern was similar to the findings in central China (Ahmad et al 2009), Japan (Minamikawa and Sakai 2005), and the USA (Wassmann et al 1994). This pattern is likely related to temperature change, soil moisture regime, soil redox condition, as well as rice growing stage (Hou et al 2000).…”

Different response of silicate fertilizer having electron acceptors on methane emission in rice paddy soil under green manuring

“…The increase in soil pH by silicate fertilizer application (Table 1) may have enhanced activity of soil microorganisms including that of methanogens and this accelerated the decomposition of organic matter with an increase in CH 4 emission. Usually, the activity of methanogens is enhanced at neutral or slightly alkaline soil conditions (Garica et al 2000) and is sensitive to variations in soil pH (Wassmann et al 1994). The minimum pH allowing the growth of 68 methanogenic species was 5.6 (Garica et al 2000).…”