The utilization of slag and biochar in croplands has been proposed as a management approach to mitigate greenhouse gas (GHG) emissions, specifically methane (CH4) and nitrous oxide (N2O), from agricultural fields. However, there is limited understanding of the long-term effects of single and combined applications of slag and biochar on GHG emissions in rice paddy fields. We investigated the legacy effects of one-year applications of slag, biochar, and slag+biochar on CH4 and N2O emissions, physicochemical properties, and rice yields during a three-year period (2016–2018) in southeast China. Over the study period, the application of slag reduced CH4 emissions by 24 %, biochar by 45 %, and the combined application of slag+biochar by 44 %. Across the study period, slag, biochar, and slag+biochar applications resulted in respective N2O emissions increases of 78 %, 63 %, and 80 %. Methane emissions contributed to approximately 70 % of the global warming potential (GWP) in the paddy field, which was reduced by 20 % with biochar application and by 15 % with the combined application of slag+biochar. Additionally, the total rice yield in the slag, biochar, and slag+biochar treatments increased by 7 %, 5 %, and 10 %, respectively, compared to the control group. Based on our findings, we recommend the combined application of slag+biochar as a sustainable rice management strategy to effectively reduce GHG emissions from paddy fields while enhancing yield production.