Alternate wetting and drying reduces methane emission from a rice paddy in Central Java, Indonesia without yield loss

Water regimes play a central role in regulating methane (CH₄) and nitrous oxide (N₂O) emissions from irrigated rice field. Alternate wetting and drying (AWD) is a possible option, but there is limited information on its feasibility under local environmental conditions, especially for tropical region. We therefore carried out a 3-year experiment in a paddy field in Central Java, Indonesia to investigate the feasibility of AWD in terms of rice productivity, greenhouse gas (GHG) emission, and water use both in wet and dry seasons (WS and DS). The treatments of water management were (1) continuous flooding (CF), (2) flooding every when surface water level naturally declines to 15 cm below the soil surface (AWD), and (3) site-specific AWD with different criteria of soil drying (AWDS) established to find out the optimum for GHG emission reduction. Gas flux measurement was conducted by a static closed chamber method. Rice growth was generally normal and the grain yield did not significantly differ among the three treatments both in WS and DS. AWD and AWDS significantly reduced the total water use (irrigation + rainfall) as compared to CF. As expected, the seasonal total CH₄ emission was significantly reduced by AWD and AWDS. On average, the CH₄ emissions under AWD and AWDS were 35 and 38%, respectively, smaller than those under CF. It should be noted that AWD and AWDS were effective even in WS due partly to the field location on inland, upland area that facilitates the drainage. The seasonal total N₂O emission did not significantly differ among the treatments. The results indicate that AWD is a promising option to reduce GHG emission, as well as water use without sacrificing rice productivity in this field.

水分管理模式对灌溉稻田甲烷（CH₄）与氧化亚氮（N₂O）的排放具有核心调控作用。干湿交替灌溉（Alternate wetting and drying, AWD）是一种可行的灌溉方案，但目前关于其在当地环境条件下的可行性研究较为匮乏，针对热带区域的相关研究尤为不足。为此，本研究于印度尼西亚爪哇中部的稻田开展了为期3年的定位试验，旨在从水稻生产力、温室气体（GHG）排放以及干湿季（WS与DS）的水分利用情况三个维度，评估AWD灌溉模式的可行性。本试验设置3种水分管理处理：(1) 持续淹水（CF）；(2) 当田面自然落干至土层下15 cm时复灌的干湿交替灌溉（AWD）；(3) 基于差异化土壤干燥阈值的定制化AWD模式（AWDS），该处理旨在筛选出温室气体减排最优的灌溉方案。气体通量采用静态密闭箱法进行测定。试验结果显示，水稻生长整体表现正常，干湿季的三种处理间籽粒产量均无显著差异。与CF处理相比，AWD与AWDS处理的总水分利用量（灌溉水+自然降雨）均显著降低。如预期所示，AWD与AWDS处理显著降低了季累计甲烷排放量。平均而言，AWD与AWDS处理的甲烷排放量较CF处理分别降低35%与38%。值得注意的是，即便在湿季，AWD与AWDS处理仍可发挥减排效果，这部分归因于试验田位于便于排水的内陆高地。三种处理间的季累计氧化亚氮排放量均无显著差异。本研究结果表明，在该试验田中，AWD灌溉模式是兼具温室气体减排与节水效果，且不会牺牲水稻产量的优良方案。