Effects of Establishment-Water Supply Method and Phosphorus Fertilizer Management on Growth, Soil Water Dynamics, and Grain Yield of Drip-Irrigated Winter Wheat

Phosphorus (P) management may interact with the method used to supply water for crop establishment in drip-irrigated winter wheat. A two-year field experiment (2023–2025) in northern Xinjiang compared pre-sowing irrigation (F) with dry sowing followed by drip irrigation for emergence (D) under three P regimes: 100% basal P (P1), 70% basal + 30% fertigated P (P2), and 50% basal + 50% fertigated P (P3). Across the years, D increased the mean 0–100 cm soil water content by 15.76% relative to F. Under D, P3 increased the soil water content by 12.53% and maturity dry matter per plant by 31.02% relative to P1. DP3 produced the highest two-year mean grain yield (8416.2 kg ha−1), which was 29.60% higher than DP1 and 33.12% higher than FP1, and also achieved the highest water-use efficiency (WUE). The significant emergence-water method × P-management interaction for yield and yield components indicated that the response to split P application depended on the establishment-water regime. Random-forest analysis identified kernels per spike, spike number, 1000-grain weight, and soil water content as the principal predictors of yield variation. Under the conditions of this two-year single-site study, dry sowing followed by drip irrigation for emergence combined with 50% basal P + 50% fertigated P improved soil water availability, late-season biomass accumulation, grain yield, and WUE; multi-site validation is required before broader recommendation.