Intercontinental comparison of greenhouse gas emissions from irrigated rice fields under feasible water management practices: Brazil and Japan

Flooded rice fields are a significant anthropogenic source of methane (CH4) and nitrous oxide (N2O) from agriculture in Asia, Latin America, and the Caribbean regions. In this work, we comparatively assessed the potential of intermittent irrigation and continuous rice flooding for reducing soil CH4 and N2O emissions, partial global warming potential (pGWP), and its yield-scaled version (YpGWP) in northwestern Japan and southern Brazil. Seasonal CH4 emissions under continuous flooded soils were slight higher in Japan (738 +/- 87kgha(-1)) than in Brazil (623 +/- 197kgha(-1)), and they were probably related to the higher level of soil organic C and the longer period under flooding in the seedling transplanting system in the Japanese site. Intermittent irrigation had similar efficiency in decreasing soil CH4 emissions in both study areas, with the maximum mitigation potential of 71% in northwestern Japan and of 62% in southern Brazil. No significant difference in seasonal soil N2O emissions (-0.17 +/- 0.05 to -0.24 +/- 0.06kgN(2)Oha(-1) in Japan and 0.32 +/- 0.08-1.16 +/- 0.40kgha(-1) in Brazil) or rice yield (7328-8064kgha(-1) in Japan and 9391-10,231kgha(-1) in Brazil) between irrigation systems was observed in either area. The potential of intermittent irrigation for reducing pGWP was around three times higher than that of continuous flooding in both sites. Thus, a reduction by 47-63% and 62-80% in yield-scaled pGWP was observed in southern Brazil and northwestern Japan, respectively. Like the well-established labor-intensive rice transplanting systems used in Asia, the introduction of feasible irrigation suppression systems in mechanized direct seeding rice fields in southern Brazil and other countries of Latin America and the Caribbean region is an effective choice for reducing greenhouse gas emissions with no adverse impact on rice yield.