Application of controlled-release urea to maintain rice yield and mitigate greenhouse gas emissions of rice-crayfish coculture field

Rice-crayfish co-culturing is an important ecological agricultural mode in China that has been rapidly developed because of its considerable environmental and economic advantages. However, the combined impacts of opti-mizing nitrogen fertilizer practices on grain yield and greenhouse gas emissions of rice-crayfish co-culture systems were not clear. In this study, four treatments were implemented, that is, a control treatment (CK), conventional fertilization treatment (CON), optimized fertilization treatment (OPT), and combined application of normal and controlled-release urea (CRF). The static chamber-gas chromatography method was used to study the dynamic emission characteristics of methane and nitrous oxide in rice-crayfish co-culture fields from 2021 to 2022, and their global warming potential and greenhouse gas emission intensity were evaluated. The results showed that the average rice yield and nitrogen fertilization partial productivity of the CRF treatment were 9444 kg ha-1 and 45.0 kg (kg N)-1, respectively, which were 0.1-12.4% and 7.2-19.1% higher than those of the other treatments. Furthermore, the CRF treatment decreased the cumulative emissions of methane and nitrous oxide by 22.2-38.3% and 25.5-33.2% respectively, compared with those of the CON and OPT treatments. The global warming potential and greenhouse gas emission intensity of the CRF treatment were 3181 and 0.35 kg CO2-eq kg-1, respectively, which were 20.9-47.0% and 25.0-57.6% lower than those of the other treatments; therefore, the CRF treatment was the optimal fertilization strategy. Among the three nitrogen fertilizer treatments, methane emissions accounted for 80.3-90.5% of global warming potential, while nitrous oxide accounted for 9.5-19.7%. Additionally, relevant analyses showed that water-dissolved oxygen was the dominant factor driving methane emissions in the rice-crayfish coculture fields. This study shows that rice-crayfish co-culturing can achieve synergy in maintaining rice yield and mitigating greenhouse gas emissions by optimizing fertilization strategies.