Reducing greenhouse gas emissions while improving rice yield and water use efficiency in rice paddies through mid-season drainage and intermittent irrigation

초록

Rice paddies are a significant source of methane (CH4), a potent greenhouse gas (GHG) with a global warming potential approximately 27 times that of carbon dioxide (CO2). Concurrently, rice serves as a staple food crop globally. As a staple food crop cultivated globally, rice occupies a large proportion of agricultural land and is associated with both high water consumption and substantial CH4 emissions. These characteristics highlight the urgent need for cultivation strategies that simultaneously improve water-use efficiency and mitigate GHG emissions. This study was conducted as a two-year (2023-2024) field experiment and assessed the effects of water management treatments involving mid-season drainage (MD) applied for either 2 weeks (2W-MD) or 3 weeks (3W-MD), with or without subsequent intermittent irrigation (II), to evaluate their impacts on GHG emissions, crop yield, and water-use efficiency in rice paddies. Soil properties and microbial community composition were analyzed to evaluate the impact of MD and II on both CH4 and N2O dynamics. The lowest cumulative CH4 emissions were observed in the 3W-MD+II treatment, showing a 74.6% reduction compared to the continuously flooded (CF) treatment. Although N2O emissions increased under MD and II, their contribution to the overall global warming potential (GWP) was relatively minor, resulting in a net reduction in GWP. The grain yield was the lowest in the CF treatment and highest in the 2W-MD+II treatment, being 16.8% greater than in the CF treatment. The most significant reduction in irrigation water use occurred in the 3W-MD+II treatment, with a 73.8% decrease compared to CF. Soil temperature demonstrated a positive correlation with CH4 flux across all treatments, while soil redox potential showed an inverse relationship with CH4 flux. Intermittent irrigation following a prolonged period of midseason drainage significantly influenced microbial community composition, favoring taxa adapted to fluctuating redox conditions. Furthermore, the evidence suggests that variations in CH4 and N2O emissions are tightly linked to shifts in microbial communities, with methaneoxidizing bacteria and denitrifiers becoming more prevalent after II, which contributed to CH4 reduction while increasing N2O emissions. Overall, the implementation of MD and II successfully reduced CH4 emissions and irrigation water use, while simultaneously enhancing crop yields and microbial diversity in paddy fields.

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