Increasing double-peak nitrogen release from controlled-release blended fertilizer boosts uptake efficiency and yield in late japonica rice in Yangtze River Delta

The objective of this study was to identify an application strategy for a blend of two controlled-release nitrogen fertilizers (CRNFs) that optimized yield and N-use efficiency of late japonica rice in the Yangtze River Delta. In a two-year field experiment using high-yield split-applied urea (CK) and no-N fertilization as control (N0), nine CRNF treatments were evaluated for their effects on grain yield, N uptake (N_UP), soil ammonium nitrogen (NH₄⁺-N) dynamics, and ammonia volatilization (AV). The treatments included sulfur-coated urea (SCU), urease inhibitor urea (AHA), 90-d polymer-coated urea (P₉₀), 120-d polymer-coated urea (P₁₂₀), and five BBFs prepared by mixing CRNFs at a 3:7 ratio (AHAP₉₀, SP₉₀, AHAP₁₂₀, SP₁₂₀, and P₉₀P₁₂₀). Based on N release characteristics, CRNFs were categorized into four release modes: pre-positioned single-peak (PrSRM), post-positioned single-peak (PoSRM), decreasing double-peak (DDRM), and increasing double-peak (IDRM). Synchronization between soil NH₄⁺-N dynamics under CRNFs and plant N uptake rate (N_UPR) under CK was quantified using dynamic time warping (DTW), with smaller values indicating higher synchrony. Results showed that single-peak release modes significantly reduced grain yield and N_UP by 12.6% and 10.5%, respectively. The IDRM treatment, a blend of 90-d and 120-d polymer-coated urea, showed NH₄⁺-N supply dynamics most closely matching the N demand of high-yielding rice, with lower two-year average DTW values (SSR_DTW 1.01, N_UPS_DTW 1.72) than DDRM (1.03 and 2.00), which translated into increases in spikelet number, grain yield, and N_UP by 4.49%, 6.03%, and 4.85%, respectively, while decreasing AV by 86.7% compared with CK. One-time application of IDRM fertilizer can align soil NH₄⁺-N supply with rice N demand, ensure high yield, and reduce N losses, providing an optimized fertilization strategy for sustainable rice production in the Yangtze River Delta.