Evaluating methane emissions from rice paddies: A study on the cultivar and transplanting date

Climate change, driven by increased greenhouse gas emissions, is a pressing environmental issue worldwide. Flooded rice paddy soils are a predominant source of methane (CH₄) emissions, accounting for approximately 11 % of global emissions. Factors such as rice (Oryza sativa L.) cultivar, transplanting date, water management, and soil characteristics significantly influence these emissions. This study aimed to evaluate the CH₄ emissions from rice paddies in relation to the cultivar and transplanting date. The experiment included two rice cultivars (an early-maturing cultivar, Unkwang, and a medium-late-maturing cultivar, Samkwang) and four transplanting dates (Times 1-4). In the present study, CH₄ emissions were higher with earlier transplanting dates and decreased significantly with delayed transplanting. Weather conditions, such as cumulative mean air temperature, cumulative soil temperature, and total sunshine hours, were positively correlated with total CH₄ emissions. The recommended regional transplanting date (Time 3) resulted in the highest rice grain yields for both cultivars. However, the earlier transplanting dates (Time 1 and Time 2) were more effective in improving plant growth characteristics such as rice straw weight, root biomass weight, and chlorophyll content. A significant positive correlation was observed between the root biomass weight of the rice and CH₄ emissions in both cultivars, implying that an increase in root biomass weight led to an increase in CH₄ emissions. Consequently, adhering to the advised regional transplanting dates is the most sensible approach for transplanting rice seedlings. This ensured lower CH₄ emissions without compromising rice productivity or quality for both cultivars. Further research should focus on identifying the most appropriate rice-transplanting dates and management practices to effectively reduce CH₄ emissions without compromising rice production.