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To evaluate the impacts of organic cropping system on global warming potentials (GWPs), field measurements of CH and NO were taken in conventional and organic rice ( Oryza sativa L.) cropping systems in southeast China. Rice paddies were under various water regimes, including continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding and moisture but without waterlogging (F-D-F-M). Nitrogen was applied at the rate of 100 kg N ha, as urea-N or pelletized, dehydrated manure product in conventional or organic rice paddies, respectively. Seasonal fluxes of CH averaged 4.44, 2.14, and 1.75 mg m h for the organic paddy plots under the water regimes of F, F-D-F and F-D-F-M, respectively. Relative to conventional rice paddies, organic cropping systems increased seasonal CH emissions by 20%, 23%, and 35% for the plots under the water regimes of F, F-D-F, and F-D-F-M, respectively. Under the water regimes of F-D-F and F-D-F-M, seasonal NO-N emissions averaged 10.85 and 13.66 μg m h in organic rice paddies, respectively, which were significantly lower than those in conventional rice paddies. The net global warming potentials (GWPs) of CH and NO emissions from organic rice paddies relative to conventional rice paddies were significantly higher or comparable under various water regimes. The greenhouse gas intensities were greater, while carbon efficiency ratios were lower in organic relative to conventional rice paddies. The results of this study suggest that organic cropping system might not be an effective option for mitigating the combined climatic impacts from CH and NO in paddy rice production. [ABSTRACT FROM AUTHOR]

Background and aims: The rice production is experiencing a shift from conventionally seedling-transplanted (TPR) to direct-seeded (DSR) cropping systems in Southeast Asia. Besides the difference in rice crop establishment, water regime is typically characterized as water-saving moist irrigation for DSR and flooding-midseason drainage-reflooding and moist irrigation for TPR fields, respectively. A field experiment was conducted to quantify methane (CH) and nitrous oxide (NO) emissions from the DSR and TPR rice paddies in southeast China. Methods: Seasonal measurements of CH and NO fluxes from the DSR and TPR plots were simultaneously taken by static chamber-GC technique. Results: Seasonal fluxes of CH averaged 1.58 mg m h and 1.02 mg m h across treatments in TPR and DSR rice paddies, respectively. Compared with TPR cropping systems, seasonal NO emissions from DSR cropping systems were increased by 49 % and 46 % for the plots with or without N application, respectively. The emission factors of NO were estimated to be 0.45 % and 0.69 % of N application, with a background emission of 0.65 and 0.95 kg NO-N ha under the TPR and DSR cropping regimes, respectively. Rice biomass and grain yield were significantly greater in the DSR than in the TPR cropping systems. The net global warming potential (GWP) of CH and NO emissions were comparable between the two cropping systems, while the greenhouse gas intensity (GHGI) was significantly lower in the DSR than in the TPR cropping systems. Conclusions: Higher grain yield, comparable GWP, and lower GHGI suggest that the DSR instead of conventional TPR rice cropping regime would weaken the radiative forcing of rice production in terms of per unit of rice grain yield in China, and DSR rice cropping regime could be a promising rice development alternative in mainland China. [ABSTRACT FROM AUTHOR]