Effects of deep storage irrigation on summer maize yield formation and safety irrigation threshold for maximizing flood resources utilization

The new strategy of deep storage irrigation through flood resources utilization is an effective alternative to addressing the water resources shortage and overexploitation of groundwater in the irrigation districts of Northern China. However, the influence mechanisms of deep storage irrigation, which is essentially characterized by active excessive irrigation, on the yield formation process of summer maize have not yet been systematically revealed. This study aimed to identify the mechanisms by which growth status and the grain filling process affect grain yield and its components under deep storage irrigation and to determine the safety threshold in different rainfall type years. A three-year field experiment (2021–2023) was conducted in the Guanzhong Plain according to six irrigation application depths (RF: 0 cm; W80 (CK): 80 cm; W120: 120 cm; W140: 140 cm; W160: 160 cm; and W180: 180 cm), with the soil saturation moisture content as the irrigation upper limit. Results showed that, compared with the W80 treatment, the W120, W140, and W160 treatments led to increased plant height (PH), leaf area index (LAI), and total dry matter accumulation (TDMA). In addition, the W120, W140, and W160 treatments enhanced the kernel weight increment achieving maximum grain filling rate (W_max), maximum grain filling rate (G_max), and active grain filling period (AGP). This resulted in increases in ear diameter (ED), ear length (EL), and 100-kernel weight (HKW), ultimately increasing the grain yield (GY). However, the higher irrigation treatment (i.e., W180) exhibited negative effects on these indicators. Relative to the W80 treatment, the W120, W140, and W160 treatments showed yield increases of 5.16 %–15.73 %, 4.77 %–14.81 %, and 4.79 %–15.34 %, respectively, over the three years. In contrast, the W180 treatment decreased the yield by 8.97 %, 9.47 %, and 10.18 %. Structural equation modeling (SEM) revealed direct influences of growth indicators (PH, LAI, and TDMA) and grain filling characteristics (W_max, G_max, and AGP) on maize yield characteristics. The growth indicators indirectly modulated the yield characteristics through grain filling characteristics. Deep storage irrigation improved ED, EL, and HKW by positively regulating W_max, G_max, and AGP, thus significantly increasing GY. This study identified the optimal threshold (W140 treatment) for maximizing maize yields and the safety threshold (W160 treatment) for maximizing flood resources utilization, and maintained relative stability in wet and normal seasons. Short-term waterlogging stress induced by W180 treatment significantly decreased the grain yield. These findings provide valuable insights for making informed decisions to balance and coordinate food security and water security under future conditions.