Optimizing the Ratio of One-Off Slow-Release Fertilizer Can Improve the Nitrogen Use Efficiency and Yield of Rice Under the Condition of Nitrogen Reduction

Increasing grain production is crucial for national food security, and fertilizer management is one of the most effective ways to achieve this. In traditional agricultural production, excessive nitrogen (N) application often leads to reduced N use efficiency and increased environmental pollution. Compound slow-release fertilizers can effectively improve N use efficiency while still meeting the nutritional demands of rice. However, research on these compound slow-release fertilizers remains limited. The effects of fertilizer management measures (controlled-release fertilizer ratios and N fertilizer levels) on rice yield, material accumulation, photosynthetic characteristics, and N use efficiency are not yet fully understood. In particular, the relationships between yield and material accumulation, photosynthetic characteristics, and N use efficiency require further study. Therefore, this study was conducted in 2021 and 2022 using Jinongda 667 as the material, with three N fertilizer rates of 90 (N1), 120 (N2), and 150 kg ha⁻¹ N (N3). Six controlled-release fertilizer ratios of sulfur-coated urea (SCU) and resin-coated urea (RCU) were tested: 1:0 (C1), 0:1 (C2), 3:1 (C3), 4:1 (C4), 5:1 (C5), and 6:1 (C6) (optimized in 2022 to three ratios: 3:1, 4:1, and 5:1, with traditional split-application fertilization (CF) added as a control). The results showed that the N3C5 treatment achieved the highest yield of 9246.7 kg ha⁻¹ among all combinations of slow-controlled release compound fertilizer ratios and N levels. In 2021, under the same N gradient, yields followed the order C5 > C4 > C3 > C2 > C1, whereas the C6 treatment exhibited a declining yield trend across different N levels. The yield pattern observed in 2022 was consistent with that of 2021. Further comparisons of C3, C4, and C5 under different N levels with the traditional fertilization treatment (N3CF) indicated that, under the same N level, the C5 treatment produced significantly higher yields than the C3 and C4 treatments. Photosynthetic rates at various stages under the C5 treatment increased by 1.9% to 12.7% compared to the C3 and C4 treatments. The N2C5 and N3C5 treatments increased yield by 1.3% and 9.4%, respectively, compared with N3CF, with effective panicle numbers increasing by 6.7% and 11.1%, respectively. The N2C5 treatment reduced N application by 20% compared with N3CF, while significantly increasing N Apparent Use Efficiency (NAUE) by 56.6% and Agronomic N Agricultural Utilization Efficiency (NAE) by 41.8%. Therefore, applying a 5:1 controlled-release fertilizer at a N application rate of 120 kg ha⁻¹ can reduce N use while enhancing efficiency. This approach provides a theoretical basis for green, high-yield rice cultivation.