Effects of Reducing Nitrogen Fertilizer Application and Combined Application of Iron Powder on the Interannual Variations of N₂O Emission from Paddy Fields and Rice Yield

Excessive application of nitrogen fertilizer is the primary cause of significant nitrous oxide (N₂O) emissions from paddy fields. Reducing nitrogen application can mitigate N₂O emissions but may lead to decreased rice yields, while iron supplementation presents a potential solution. This study conducted 3-year in-situ field experiments with seven treatments, including conventional nitrogen application (100%N), 80% of conventional nitrogen (80%N), 60% of conventional nitrogen (60%N), no nitrogen application (0%N), and treatments with iron powder supplementation under reduced nitrogen levels (80%N + Fe, 60%N + Fe, 0%N + Fe). The aim was to explore the effects of iron powder supplementation under reduced nitrogen conditions on N₂O emissions and rice yield in paddy fields. The results show that while rice yields following the 80%N + Fe treatment were comparable with those under the 100%N treatment in both 2022 and 2023, it significantly outperformed the 80%N treatment in 2023 (P<0.05). In 2023, the cumulative N₂O emissions under 80%N, 80%N + Fe, 60%N, and 60%N + Fe treatments were significantly reduced by 76.7%, 68.4%, 94.0%, and 99.8%, respectively, compared to the 100%N treatment (P<0.05). Interannual variability in environmental conditions or climatic parameters and nitrogen application levels significantly affected rice yield and cumulative N₂O emissions, while nitrogen application levels also significantly influenced N₂O emission intensity (P<0.05). Correlation analysis revealed that cumulative N₂O emissions were significantly correlated with soil moisture, electrical conductivity, and nitrate nitrogen contents over the 3-year experiment (P<0.05). Both random forest and structural equation modeling identified nitrate nitrogen as the most critical factor influencing cumulative N₂O emissions. Integrating results from the 2021-2023 rice-growing seasons, rice yield showed a highly significant positive correlation with cumulative N₂O emissions (P<0.001). Long-term 20% nitrogen reduction combined with iron powder supplementation demonstrated comprehensive benefits in maintaining rice yield and mitigating N₂O emissions, offering positive implications for ensuring food security, reducing nitrogen fertilizer use, and alleviating environmental impacts.