Synchronized Postponement of Nitrogen, Phosphorus, and Potassium Fertilizers Alleviates Wheat Yield Loss Under Spring Low-Temperature Stress by Improving Nutrient Utilization Efficiency

Spring low-temperature stress (SLTS) frequently occurs during the critical stage from stamen and pistil differentiation to anther connective formation in wheat, severely disrupting young spike development and reducing grain yield (GY). Although synchronized nitrogen (N), phosphorus (P) and potassium (K) fertilization can alleviate SLTS-induced damage, the optimal basal–topdressing ratio of P and K fertilizers remains unclear. In this study, three temperature regimes (11 °C, 4 °C, and −4 °C) and four N-P-K basal–topdressing ratios (10:0, 7:3, 5:5, and 3:7) were evaluated for their effects on soil nutrient availability, plant N/P/K uptake and utilization, and grain yield in wheat cultivar Yannong 19 exposed to spring low-temperature stress at the anther connective stage. The results showed that SLTS suppressed soil organic carbon content, reduced soil nutrient availability, suppressed photosynthesis and soluble sugar accumulation, decreased fertilizer use efficiency, and significantly reduced grain number per spike, 1000-grain weight, and GY. Synchronized postponement of N, P, and K fertilizers (R2–R4) stimulated soil organic carbon decomposition, increased soil total N, available P and available K contents, reduced soil C/N and N/P stoichiometric ratios, enhanced plant nutrient uptake and translocation, improved photosynthetic capacity and cold resistance, and promoted dry matter accumulation. Consequently, grain number per spike, 1000-grain weight and GY increased by up to 11.2%, 6.3% and 38.5%, respectively, under postponed fertilization regimes. Among all modes, R3 (5:5) exhibited the best overall performance. These findings demonstrate that synchronized postponement of N, P, and K fertilizers, particularly with a balanced basal—topdressing ratio, is an effective strategy to mitigate SLTS-induced yield losses in wheat by improving soil nutrient supply, plant physiological status, and fertilizer efficiency.