Twice-Split Phosphorus and Potassium Fertilizers Application Alleviates Wheat Yield Loss Under Spring Low Temperature Stress by Improving the Utilization Efficiency of Nitrogen and Phosphorus Nutrients

Spring low temperature stress (SLTS) frequently occurs during with 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 postponed phosphorus (P) and potassium (K) fertilization can alleviate SLTS-induced damage, but the optimal basal–topdressing ratio of P and K fertilizers remains unclear. In this study, wheat cultivar Yannong 19 was subjected to three temperature regimes (11℃, 4℃, and −4℃) at the anther connective stage in climate chambers, and four P-K fertilization modes with basal: topdressing ratios of 10:0 (R1, control), 7:3 (R2), 5:5 (R3), and 3:7 (R4) were evaluated. The effects of these treatments on soil nutrient availability, plant N/P/K uptake and utilization, and GY were investigated. Results showed that SLTS inhibited soil organic carbon decomposition, 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. Postponed P-K fertilization (R2-R4) promoted organic carbon mineralization, 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, grains 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 postponed P-K fertilization, 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.