Optimizing subsoiling depth to enhance soil water storage and annual crop water productivity in wheat-maize cropping system

Subsoiling effectively enhances crop water productivity (CWP) by optimizing soil structure. Nevertheless, the effects of different subsoiling depths on cross-seasonal soil water utilization and CWP remain unclear. This study aimed to evaluate effects of four tillage methods (conventional tillage at 25 cm depth (CT25); subsoiling at 30 cm (ST30); 35 cm (ST35); and 40 cm depths (ST40)) on soil structure, hydraulic properties, and CWP during 2016–2018 winter wheat-summer maize cropping system. Results revealed that all subsoiling depths improved soil structure and hydraulic properties compared to conventional tillage. ST35 and ST40 increased total porosity by 4.83–7.78 % while reducing bulk density by 3.11–8.17 % compared to CT25. Soil water infiltration rates were significantly higher under subsoiling than CT25. At maize maturity, ST30, ST35 and ST40 maintained significantly higher soil water storage (SWS) in the 0–40 cm layer compared to CT25, with increases of 16.78 %, 0.65 %, and 7.97 %, respectively. The Partial Least Squares Path modeling revealed that SWS at maize harvest significantly enhanced subsequent wheat-sowing SWS (p < 0.01), demonstrating cross-seasonal water carryover. Consequently, subsoiling increased CWP by 10.9–15.9 % and 9.8–11.9 % during the maize and wheat seasons, respectively, compared to CT25. ST35 optimized 0–40 cm soil structure while enhancing maize-season SWS. The stored water alleviated subsequent wheat-season water deficits, thereby increasing annual CWP in the wheat-maize system. ST35 is recommended as an optimal tillage practice for sustainable plough layer construction in eastern Shandong Province, China. The findings provide new insights for water-efficient tillage systems to enhance annual crop productivity in the North China Plain.