A High Proportion of Basal Nitrogen Application Mitigates Straw Return-Induced Nitrogen Immobilization and Sustains Winter Wheat Yield on the Jianghan Plain

Winter wheat (Triticum aestivum L.) productivity in intensive rice–wheat systems of the Jianghan Plain is constrained by sub-optimal nitrogen (N) management and residue handling. Straw residue return (SRR) can increase soil organic carbon and improve soil structure but may also immobilize N and alter the temporal pattern of soil mineral N (SMN). Although straw return and N fertilization have been widely studied, the combined effects on SRR and N applications on wheat yield and soil N dynamics in this region remain insufficiently resolved. In this study, we evaluated three SRR levels (0, 50, and 100% of approximately 3.5 t rice straw ha−1) combined with four N application treatments over three years of field trials in the Jianghan Plain of Yangtze River Basin. Treatments were arranged in a randomized complete block design. Our results show that wheat performance is closely associated with SMN (NO3−-N, NH4+-N, total N) at 0–20 soil layers from booting to maturity. Grain yield increased sharply with N application, with SRR further enhancing yield. The combination of a 100% SRR and 70/30 basal-to-overwinter N split with a total N rate of 180 kg ha−1 (T11) achieved the highest three-year mean grain yield. This superior performance was driven by optimized yield components, including a maximum of 55 grains per spike and a 1000-grain weight of 42.4 g under T11. Soil total N, nitrate-N, ammonium-N, and SOC were all significantly influenced by both N application timing and SRR. Across the three-year experiment, we concluded that 50–100% SRR combined with 70–100% basal N application represents an optimal agronomic practice for rice–wheat rotations in the Jianghan Plain.