Water–Nitrogen Coupling Under Film Mulching Synergistically Enhances Soil Quality and Winter Wheat Yield by Restructuring Soil Microbial Co-Occurrence Networks

Improper irrigation and fertilization can easily lead to soil nutrient imbalance, inhibit microbial reproduction, and thereby reduce soil quality and crop yield. This study conducted winter wheat planting experiments in 2023-2025, setting three muddy water (sediment-laden irrigation water) treatments of different sediment concentrations (3, 6 and 9 kg·m^-3), irrigation levels (0.50-0.65, 0.65-0.80 and 0.80-0.95 FC), and nitrogen application rates (100, 160 and 220 kg·ha^-1). An L9(3³) orthogonal experimental design was applied to evaluate the influence of water and nitrogen regulation on soil properties, microbial community structure, and wheat productivity. The results showed the following: Among these treatments, the T5 treatment (6 kg·m^-3, 0.65-0.80 FC, 160 kg·ha^-1) significantly improved the root zone environment, and the total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), and soil organic carbon (SOC) content also increased significantly. T5 also enhanced the diversity and network complexity of bacterial and fungal communities. Notably, genera such as <i>Lysobacter</i>, <i>Lasiobolidium</i>, and <i>Ascobolus</i> became central to nitrogen transformation and nutrient cycling. Structural equation modeling revealed the interdependent mechanism between soil quality, microorganisms, and wheat yield: NO₃^--N and SOC drive improvements in soil quality, while microbial community structure and network complexity are key to yield increases, with fungal communities making the largest direct contribution to yield (<i>R</i>² = 0.93). The T5 treatment increased two-year yields by 21.34-24.96% compared to conventional irrigation and fertilization (CK2), improved irrigation water use efficiency by 56.40-57.51% and peak nitrogen agronomic efficiency. The synergistic effect of "soil quality optimization-enhanced microbial activity-efficient utilization of water and nitrogen-high wheat yield" has been achieved, providing a theoretical basis and practical reference for scientific water and nitrogen management and sustainable yield increase in winter wheat in the Yellow River Basin and similar areas.