Subsoiling tillage increases water-use efficiency of winter wheat by improving soil hydraulic properties associated with pore structure in the North China Plain

Subsoiling is widely used to improve soil productivity in the North China Plain (NCP). However, its effects on pore network-based hydraulic properties and their relationship with water use efficiency (WUE) are far from clear. In this study, we evaluated the effects of three tillage systems (rotary tillage at 15 cm depth, RT15; subsoiling at 40 cm depth, SS40; and subsoiling at 35 cm depth, SS35) on soil pore structure, hydraulic properties, and WUE during the 2022–2024 winter wheat seasons. Results showed that the effects of SS40 and SS35 were similar in optimizing the soil pore structure and hydraulic properties. Compared with RT15, SS40 and SS35 increased the soil macroporosity ratio, the soil pore connectivity, and the soil water storage. Structural equation modeling revealed that optimized soil pore structure under subsoiling directly and positively influenced the WUE or indirectly increasing the soil water storage. As a result, compared with RT15, SS40 and SS35 increased the spike number, kernel number per spike, and 1000-grain weight, and ultimately improved the yield (35.59% and 39.32%, respectively) and WUE (36.69% and 41.55%, respectively). Overall, the results revealed the mechanism of high-efficiency water use from the perspective of pore network-based hydraulic properties, providing a theoretical basis for food security.