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A 3-year field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions from rice paddies under various agricultural managements including water regime, crop residue incorporation, and synthetic fertilizer application. In contrast with continuous flooding, midseason drainage incurred a drop in CH4 fluxes while triggering substantial N2O emission. Moreover, N2O emissions after midseason drainage depended strongly on whether or not fields were waterlogged due to intermittent irrigation. Urea application tended to reduce CH4 emissions but significantly increased N2O emissions. Under a water regime of flooding-midseason drainage-reflooding-moist intermittent irrigation but without water logging (F-D-F-M), both wheat straw and rapeseed cake incorporation increased CH4 emissions by 25 2%, and rapeseed cake increased N2O by 17% while wheat straw reduced N2O by 19% compared to controls. Seasonal average fluxes of CH4 ranged from 25.4 mg m-2 d-1 when no additional residue was applied under the water regime of flooding-midseason drainage- reflooding to 116.9 mg m-2 d-1 when wheat straw was applied at 2.25 t ha-1 under continuous irrigation flooding. Seasonal average fluxes of N2O varied between 0.03 mg N2O-N m-2 d-1 under continuous flooding and 5.23 mg N2O-N m-2 d-1 under the water regime of F-D-F-M. Both crop residue-induced CH4, ranging from 9 to 15% of the incorporated residue C, and N2O, ranging from 0.01 to 1.78% of the applied N, were dependent on water regime in rice paddies. Estimations of net global warming potentials (GWPs) indicate that water management by flooding with midseason drainage and frequent water logging without the use of organic amendments is an effective option for mitigating the combined climatic impacts from CH4 and N2O in paddy rice production. [ABSTRACT FROM AUTHOR]

Abstract A model developed by the authors (Huang et al. 1998) was further validated against field measurements from various regions of the world and calibrated to estimate methane emission from irrigated rice cultivation of China. On the basis of available information on rice cultivated area, growth duration, grain yield, soil texture and temperature, methane emission from Chinese rice paddies was estimated for 28 rice cultivated provinces in mainland. The calculated daily methane emission rates, on a provincial scale, ranged from 0.15 to 0.86 g m–2 with an average of 0.32 g m–2. Five of the top six locations with higher daily methane emissions are located at a latitude between 28° and 31° N. A total amount of 9.66 Tg (1 Tg = 1012 g) CH4 per year, ranging from 7.19 to 13.62, was estimated to be released from Chinese rice paddy soils. Of the total, 45% is emitted from the single-rice growing season, and 19% and 36% are from the early-rice and the late-rice growing seasons, respectively. Approximately 70% of the total is emitted in the region located at latitude between 25° and 32° N. The emissions from rice fields in Sichuan and Hunan Province were calculated to be 2.85 Tg y–1, accounting for ≈ 30% of the total. Comparisons of the estimated and the observed emission rates show that the estimates were, in general, close to the measurements at most locations. [ABSTRACT FROM AUTHOR]

Abstract Reliable regional or global estimates of methane emissions from flooded rice paddy soils depend on an examination of methodologies by which the current high variability in the estimates might be reduced. One potential way to do this is the development of predictive models. With an understanding of the processes of methane production, oxidation and emission, a semi-empirical model, focused on the contributions of rice plants to the processes and also the influence of environmental factors, was developed to predict methane emission from flooded rice fields. A simplified version of the model was also derived to predict methane emission in a more practical manner. In this study, it was hypothesized that methanogenic substrates are primarily derived from rice plants and added organic matter. Rates of methane production in flooded rice soils are determined by the availability of methanogenic substrates and the influence of environmental factors. Rice growth and development control the fraction of methane emitted. The amount of methane transported from the soil to the atmosphere is determined by the rates of production and the emitted fraction. Model validation against observations from single rice growing seasons in Texas, USA demonstrated that the seasonal variation of methane emission is regulated by rice growth and development. A further validation of the model against measurements from irrigated rice paddy soils in various regions of the world, including Italy, China, Indonesia, Philippines and the United States, suggests that methane emission can be predicted from rice net productivity, cultivar character, soil texture and temperature, and organic matter amendments. [ABSTRACT FROM AUTHOR]