Can optimizing nitrogen management improve net ecosystem economic benefits in rice cultivation?

Although optimizing nitrogen management (Nitrogen fertilizer reduction, NFR; organic fertilizer substitution, OFS) is the feasible solution for reducing pollutant emissions (NH3 volatilization, greenhouse gas emissions, and N leaching and runoff) in rice cultivation, the different revenue and cost results in an indefinite net ecosystem economic benefit (NEEB) is the major hindrance when promoting these nitrogen strategies. Investigating and assessing the NEEB could exhibit the suitability of different nitrogen management. In a two-year field experiment, the conventional nitrogen management (N180), NFR (25% nitrogen reduction based on N180), and OFS (25% N substituted with organic fertilizer based on N180) were compared under continuous flooding irrigation (CF) and alternating wet and dry irrigation (AWD). Both NFR and OFS showed significant reductions in NH3 volatilization (25.0% and 18.9%), GHG emissions (35.4% and 28.6%), and total N leaching and runoff (39.0% and 28.1%), compared to N180. However, NFR resulted in a 19.0% reduction in rice yield and a lower NEEB (15.5 x 103 CNY ha-1) than N180 (27.4% lower). Similarly, OFS produced an identical NEEB (15.6 x 103 CNY ha-1) as NFR due to the high cost of organic fertilizer in rice production. Furthermore, AWD irrigation showed better environmental and economic benefits than CF, reducing CH4 emissions and conserving irrigation water and electricity. While NFR and OFS reduced the NEEB in rice cultivation, the recommendation is coupling NFR with other field practices to improve yield revenue, reducing organic fertilizer production costs and maintaining long-term application, both of which will potentially enhance the NEEB when applying these optimizing nitrogen managements.