Rice production accounts for 15% of the national Greenhouse Gas (GHG) emissions and Vietnam aims at reducing emissions from rice production by focusing on changing farming practices. However, the potential for mitigation through the selection of different rice varieties is still poorly understood. A two-year field screening of 20 rice varieties under continuous flooding (CF) and alternate wetting and drying (AWD) irrigation was conducted in the Vietnamese Mekong Delta (VMD), Vietnam, employing the closed chamber method for assessing GHG emissions. The results confirmed that varietal variation was the largest for methane (CH₄) emissions under CF. Across the varietal spectrum, CH₄ emissions were more important than nitrous oxide (N₂O) (accounts for less than 2% of the CO₂e) with the lowest emitting variety showing 243 kg CH₄ ha⁻¹ and the highest emitting variety showing 398 kg CH₄ ha⁻¹ emissions as compared to 0.07 kg N₂O ha⁻¹ and 0.76 kg N₂O ha⁻¹ emissions, respectively. Under AWD, CH₄ emissions were generally strongly reduced with the varietal effect being of minor importance. Compared with IPCC default values, the data set from the two seasons yielded higher Emission Factors (EFs) under CF (2.92 and 3.00 kg ha⁻¹ day⁻¹) as well as lower Scaling Factors (SFs) of AWD (0.41 and 0.38). In the context of future mitigation programs in the VMD, the dry season allows good control of the water table, so varietal selection could maximize the mitigation effect of AWD that is either newly introduced or practised in some locations already. In the wet seasons, AWD may be difficult to implement whereas other mitigation options could be implemented such as selecting low-emitting cultivars.

中文翻译：

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越南湄公河三角洲不同水管理下水稻生产系统温室气体排放的品种影响

稻米生产占全国温室气体 (GHG) 排放量的 15%，越南旨在通过重点改变耕作方式来减少稻米生产的排放。然而，人们对通过选择不同水稻品种来缓解气候变化的潜力仍知之甚少。在越南湄公河三角洲 (VMD)，对连续淹水 (CF) 和干湿交替 (AWD) 灌溉下的 20 个水稻品种进行了为期两年的田间筛选，采用密闭室方法评估温室气体排放。结果证实， CF 下甲烷 (CH ₄ ) 排放量的品种变化最大。在整个品种谱中，CH ₄排放量比一氧化二氮 (N _{2 O)（占 CO 2} e的不到 2% ）更重要，排放量最低的品种为 243 kg CH ₄ ha ⁻¹，排放量最高的品种为显示 398 kg CH ₄ ha ^-1排放量，而排放量分别为 0.07 kg N ₂ O ha ^-1和 0.76 kg N ₂ O ha ^-1。在 AWD 下，CH ₄排放量普遍大幅减少，品种影响并不重要。与IPCC默认值相比，两个季节的数据集在CF下产生了更高的排放因子（EF）（2.92和3.00 kg ha ^-1 day ^-1）以及更低的AWD缩放因子（SF）（0.41和0.38） 。在 VMD 未来缓解计划的背景下，旱季可以很好地控制地下水位，因此品种选择可以最大限度地发挥 AWD 的缓解效果，无论是新引入的还是在某些地方已经实施的 AWD。在雨季，全轮驱动可能难以实施，而可以实施其他缓解措施，例如选择低排放品种。