Nitrogen fertilization in rapeseed-rice rotation affects methane emissions from rice fields. The study found that applying nitrogen during the rapeseed season increased methane emissions during the rice seedling stage. This was due to higher soil carbon and ammonium levels. The residual effects of nitrogen fertilizer contributed significantly to methane emissions throughout the rice-growing season. Additionally, nitrogen fertilization in both rapeseed and rice seasons led to increased rice plant biomass. Overall, the study highlights the importance of considering residual nitrogen effects on methane emissions in rice fields under rotation systems.