Japan Society for the Promotion of Science, Chiyoda, Tokyo 102-0083, Japan; Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan; Graduate School of Horticulture, Chiba University, 648, Matsudo, Chiba 271-8510, Japan.
Sci Total Environ. 2022 Oct 10;842:156958. doi: 10.1016/j.scitotenv.2022.156958. Epub 2022 Jun 24.
For sustainable food production in the Mekong Delta, greenhouse gas (GHG) emissions from rice cropping activities need to be reduced without sacrificing rice productivity. Each year, a substantial amount of straw is incorporated into paddy soils through triple rice cropping, which is characterized by a short cropping period and nearly year-round flooding, such that a large amount of methane is emitted. Exposing these soils to oxidative conditions by altering the cropping-period water regime might have the potential to reduce GHG emissions with increased rice yield. To test this potential, a split-plot experiment was conducted in a typical triple-cropped alluvial farmer's paddy in a central delta area over five years and 15 consecutive cropping seasons. The emissions observed from the continuously inundated paddies were 1.1-2.7 times greater than the reported emission factors for Vietnamese continuously inundated paddies. A significantly higher emission peak was detected at the beginning of the rice cropping and flooding fallow periods in continuously flooded (CF) paddies than in alternate wetting and drying (AWD) paddies, although the differences in field water level and soil moisture among the paddies were negligible. AWD reduced annual methane emissions (-51 %) and increased rice yield (+9 %), presumably through enhanced translocation of carbohydrates from leaves to panicles. The amount of GHGs emitted from straw use also decreased (11 %) under AWD management because the straw production rate was significantly lowered (9 %) by enhanced nutrient translocation. These results indicate that GHG emission reduction potentials in the Mekong Delta have been underestimated by previous studies, corroborate the necessity of additional long-term observations of triple rice cropping systems and demonstrate the need for a robust methodology for monitoring the permanence of AWD effects after policies promoting its widespread dissemination take effect.
为了实现湄公河三角洲的可持续粮食生产，需要在不牺牲水稻生产力的情况下减少水稻种植活动中的温室气体（GHG）排放。每年，通过三季稻种植将大量稻草纳入稻田土壤，三季稻种植的特点是种植期短且几乎全年淹没，因此会排放大量甲烷。通过改变种植期的水情来使这些土壤处于氧化条件下，可能有潜力减少 GHG 排放并增加水稻产量。为了验证这种潜力，在湄公河三角洲中部地区的一个典型的三季稻冲积农民稻田中进行了为期五年和 15 个连续种植季节的裂区实验。与越南连续淹没稻田的报告排放因子相比，连续淹没稻田（CF）中观察到的排放量高出 1.1-2.7 倍。在连续淹水（CF）稻田中，在水稻种植和淹水休耕期开始时检测到明显更高的排放峰值，而在交替湿润和干燥（AWD）稻田中则没有，尽管稻田之间的田间水位和土壤水分差异可以忽略不计。AWD 减少了甲烷的年排放量（-51%）并增加了水稻产量（+9%），这可能是通过增强碳水化合物从叶片向穗的转运实现的。在 AWD 管理下，稻草使用产生的 GHG 排放量也减少了（11%），因为通过增强养分转运，稻草的产量显著降低（9%）。这些结果表明，以前的研究低估了湄公河三角洲的 GHG 减排潜力，证实了对三季稻种植系统进行更多长期观测的必要性，并表明在推广其广泛应用的政策生效后，需要一种强大的方法来监测 AWD 效应的持久性。
