Soil water dynamics in mid-season rice fields under deficit irrigation

【Objective】Soil water movement plays a crucial role in root water uptake and redistribution across the soil profile. Understanding its response to biotic and abiotic factors is essential for improving soil water use efficiency. This study investigates soil water dynamics in mid-season rice fields under deficit irrigation.【Method】The experiment was conducted in a rice field in the Poyang Lake Basin, where deficit irrigation was applied during four critical growth stages: early and middle jointing-booting, heading-flowering, and milking stages. A fully irrigated field served as the control. Soil moisture content was measured at depths from 15 cm to 210 cm. Water consumption, water consumption intensity, soil water movement, and moisture variations were analyzed under different irrigation treatments. 【Result】① Deficit irrigation significantly affected soil moisture in the 15-60 cm layer but had minimal impact below 110 cm. Across all growth stages, soil moisture initially declined and then stabilized. The largest moisture reductions occurred at 25 cm (early and middle jointing-booting), 35 cm (heading-flowering), and 45 cm (milking), with corresponding moisture contents of 30%, 25%, 35%, and 35%, respectively. ② During early and middle jointing-booting, water consumption decreased with depth, whereas at the heading-flowering and milking stages, it increased below 15 cm. Compared to full irrigation, deficit irrigation reduced total water consumption by 40.0% (early jointing-booting), 25.7% (middle jointing-booting), 56.6% (heading-flowering), and 14.5% (milking). Water consumption intensity followed the order: middle jointing-booting＞milking＞early jointing-booting＞heading-flowering, with reductions of 15.2%, 37.5%, 39.5%, and 56.0%, respectively. ③ The greatest fluctuations in soil moisture occurred between 12:00—18:00, followed by 06:00—12:00, indicating significant water deficits during these periods. Some replenishment occurred in the 15 and 60 cm layers between 00:00—06:00 and 18:00—24:00, especially during the heading-flowering stage.【Conclusion】During seasonal droughts, irrigation should be carefully managed to ensure water reaches the root zone while minimizing evaporation and percolation. Irrigation should be prioritized during the jointing-booting stages, with optimal amounts of 56 mm (early jointing-booting), 85 mm (middle jointing-booting), 56 mm (heading-flowering), and 73 mm (milking), applied within 18, 13, 17, and 14 days, respectively, after plants enter each stage. These findings provide insights for optimizing water use and improving mid-season rice yield in the study region.