Multi-objective decision-making for efficient utilization of water and fertilizer in paddy fields: A case study in Southern China

Effective water and fertilizer management modes (WFMMs) are crucial for mitigating non-point source pollution, enhancing grain quality, and improving resource utilization in paddy fields. Nevertheless, screening WFMMs that can effectively synergize these benefits is challenging, particularly in the wake of climate change. A two-year lysimeter experiment was conducted to investigate the effects of WFMMs on water balance components, nitrogen and phosphorus loss loads, grain yield and quality, and nitrogen utilization efficiency. Four treatments were established, including flooding irrigation (FI) and alternate wetting and drying irrigation (AWD), paired with conventional fertilizers (CF) and sulfur-coated fertilizer (SCF). A multi-criteria evaluation framework was developed to assess the potential values of WFMMs under diverse hydrological conditions using the vertical and horizontal scattering degree method. The results indicated that the AWD regime increased irrigation and drainage by approximately 8% compared to CF during the wet season, while reducing irrigation, percolation, and augmenting capillary rise during the dry season. Irrigation had not a significant effect on rice yield and quality. Compared to CF, AWD significantly increased nitrogen accumulation at maturity and nitrogen recovery efficiency by 20% and 31% on average. The SCF had a significant effect on the nitrogen accumulation at maturity, nitrogen recovery efficiency, N partial factor productivity, yield (increased 8–9% across two years), and protein content (increased ∼8% across two years), but at the cost of higher leachate concentration when compared to CF. Integration of AWD and SCF treatments demonstrates the potential for improved water productivity, yield, and nitrogen utilization efficiency, along with an enhanced ability to purify pollutants. The vertical and horizontal scattering degree method assessment showed that the AWD+SCF treatment exhibits superior performance in water saving, pollution reduction, yield and quality, and nitrogen efficient utilization, which was amplified during the dry season. These findings offer novel perspectives for optimizing WFMMs under varying hydrological conditions in hilly areas of Southern China.