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.

There are few studies on how nitrogen (N) fertilizer application rates and transplanting densities impact rice yield, root distribution, and N use efficiency in the cold regions of Northeast China. This research involved a two-year field trial utilizing Jinongda 667 as the material. In 2021, three N split-fertilizer applications—T1 (6:3:1), T2 (5:3:2), T3 (4:3:3)—and two transplanting densities—D1 (30 cm × 13.3 cm) and D2 (30 cm × 20 cm)—were compared with the conventional cultivation mode (T0: 175 kg N hm⁻², 6:3:1), whereby the N application mode most suitable for increasing density was explored. In 2022, four N application levels—0 (N0), 125 (N1), 150 (N2), and 175 (N3) kg N hm⁻²—were assessed under the same density treatment to analyze the yield, resource utilization efficiency, and root traits of Jinongda 667. The results indicated that when the transplanting density was 30 cm × 13.3 cm, the application of 5:3:2 fertilizer was more conducive to improving rice yield. Increasing planting density under reduced N input significantly enhanced both rice yield and N use efficiency. In contrast to the conventional cultivation method (D2N3), the treatment of increased planting density (D1N2) under reduced N input led to a 21.2% rise in the number of panicles per square meter and an 8.6% boost in rice yield. Furthermore, increasing planting density under reduced N input significantly enhanced the agronomic efficiency of N fertilizer, the apparent utilization rate, and the N harvest index. It also boosted the SPAD value, photosynthetic rate, and the utilization efficiency of light and N resources in rice. However, it was noted that root enzyme activity decreased. This study demonstrated that increasing planting density, combined with the N application mode of 5:3:2 and an N application rate of 150 kg hm⁻², maximized resource utilization efficiency, optimized root absorption capacity, and resulted in higher yields.

Background: In Northeast China’s cold rice (Mollisol) regions, low temperatures slow straw decomposition, causing early microbial nitrogen (N) immobilization that competes with crop demand. Delayed N release from slow-release fertilizer (SRF) exacerbates this deficit, hindering high yield and grain quality. Methods: A two-year (2024–2025) pool planting experiment was conducted on rice ‘Jinongda 667’ with a total N application rate of 150 kg ha⁻¹. Six treatments were established: a 7:3 blend of slow-release fertilizer and urea, alongside controls of conventional urea and slow-release fertilizer alone, under both straw removal and incorporation conditions. Results: This blend increased grain yield by 6.64–7.75% over conventional urea, achieving the highest yield among all treatments, whereas SRF alone under straw incorporation reduced yield by 7.57% relative to N + S. The 30% urea (45 kg N ha⁻¹) alleviated immobilization deficit (15–30 kg N ha⁻¹) during the tillering-to-jointing stage, promoting root growth and panicle formation, while 70% SRF sustained N supply during mid-to-late stages, delaying senescence and enhancing photosynthesis. At peak grain filling, SSS and SBE activities increased by 94.01% and 10.53–11.08%, respectively. Under straw incorporation, it reduced chalky grain rate by 4.56–35.55% and chalkiness by 1.77–41.86%, increased protein content by 0.47–6.95% and gel consistency by 43.59–52.99%, decreased amylose by 2.2–5.77%, and optimized RVA profiles. Conclusions: The 7:3 blend synchronizes N supply with crop demand through temporal complementarity with straw nutrient dynamics, offering a one-time fertilization strategy for achieving high yield and quality under straw incorporation. However, given inter-annual variation (2024–2025) in tillering and N accumulation, its performance may be sensitive to climatic fluctuations, warranting further validation under diverse conditions.