Optimizing Fertilization Strategies to Reduce Carbon Footprints and Enhance Net Ecosystem Economic Benefits in Ratoon Rice Systems

Ratoon rice is a planting system that efficiently utilizes temperature and light resources. However, multiple fertilization applications are typically required to maintain stable rice yields. Improper fertilization not only poses challenges to scarce labor resources but also increases carbon footprints (CFs). Research on the effects of different fertilization strategies on greenhouse gas (GHG) emissions, yield, CF, and ecosystem net economic benefits (NEEBs) in ratoon rice systems remains limited. A two-year field experiment was conducted to evaluate the effects of one conventional fertilization strategy and four optimized fertilization strategies on GHG emissions, yield, CF, and NEEBs in the ratoon rice system. The conventional fertilization strategy applied urea in five splits (FFP, 280 kg N·ha−1). The optimized strategies included (1) one-time side deep application controlled-release fertilizer (CRF, 280 kg N·ha−1); (2) CRF with 20% N replaced by organic fertilizer (OF + CRF1); (3) the same as (2) with a 10% N reduction (OF + CRF2, 252 kg N·ha−1); and (4) the same as (2) with a 20% N reduction (OF + CRF3, 224 kg N·ha−1). The results showed that compared with FFP, optimized fertilization treatments reduced CH4 and N2O emissions by 28.69% to 55.27% and 25.08% to 40.32%, respectively. They also increased the annual rice yields by 2.22% to 19.52% (except OF + CRF3). Optimizing fertilization treatments reduced annual CF, CFY, and CFEC by 26.66% to 49.59%, 34.11% to 51.12%, and 25.35% to 41.47%, respectively. These treatments also increased NEEBs by 8.27% to 34.23%. Among them, OF + CRF1 and OF + CRF2 treatments achieved the highest NEEB. In summary, CRF treatments can balance ratoon rice yield and environmental benefits. Replacing part of the N with organic fertilizer further enhances annual yield and NEEBs.