Side-deep slow-release nitrogen fertilization combined with panicle-stage urea topdressing improves energy efficiency, reduces carbon footprint, and enhances economic performance in rice systems.

Introduction: Although both side-deep placement and slow-release nitrogen fertilizer (SRF) have been widely recognized as effective strategies for improving nitrogen use efficiency in rice, the effects of integrating side-deep slow-release nitrogen fertilization combined with urea topdressing on energy efficiency, carbon footprint (CF), and economic performance remain unclear. Methods: In this study, seven N treatments were established: no N (0N), traditional fertilization (CK), side-deep placed urea (DU), side-deep placed SRF (DSU), and DSU supplemented with 30% urea at basal, tillering, or panicle stages (DSU+U, DSU+TU, DSU+PU). We systematically evaluated the combined effects of integrating side-deep slow-release nitrogen fertilization combined with urea topdressing on rice productivity, energy input-output structure, CF, and economic performance. Results: Compared with CK, side-deep placed SRF treatments significantly increased rice yield by 10.65%-23.54%. Under similar total energy inputs, side-deep placed SRF significantly enhanced energy output and net energy, with energy use efficiency (EUE), energy productivity (EP), and energy profitability (EPF) increasing by 9.62%-22.40%, 8.88%-22.86%, and 10.34%-24.07%, respectively, while specific energy (SE) was reduced. Although side-deep placed SRF increased indirect greenhouse gas emissions, substantial reductions in field CH Discussion: Overall, DSU+PU represents a practical cleaner-production strategy that simultaneously enhances energy use efficiency, reduces carbon footprint, and improves economic viability, providing an effective pathway toward sustainable rice production.