Co-applying mild alternate wetting and drying with biochar synergistically improves rice yield and quality

To address the dual challenges of water scarcity and rising demand for premium rice, this study investigated the synergistic effects of mild alternate wetting and drying (Mild AWD) irrigation combined with wheat straw biochar application on rice yield and grain quality. A two-year field experiment (2023–2024) was conducted with the hybrid rice cultivar Yongyou 2640, with two irrigation regimes: continuous flooding (CF) and Mild AWD (re-irrigation at a soil water potential of –10 to –15 kPa at 15–20 cm depth), with or without a one-time biochar application (10 t ha⁻¹). The results showed that co-application of Mild AWD and biochar significantly increased grain yield by 18.7% in 2023 and 13.4% in 2024 compared to CF alone. It also comprehensively improved grain quality: milling quality (head rice rate increased by 23.1–24.6%), appearance quality (chalkiness reduced by 36.4–38.2%), cooking and eating quality (higher peak viscosity and lower gelatinization temperature and enthalpy), and nutritional quality (increased glutelin and decreased prolamin content and starch digestion). These improvements were attributed to enhanced root activity alongside leaf photosynthetic rate, which promotes the accumulation of photoassimilates in vegetative organs and their translocation to grains. Moreover, elevated activities of key starch synthases further enhanced starch biosynthesis and accumulation, which underpinned the improved yield and superior quality. We also identified that a minimum soil water potential of –10 to –15 kPa at a depth of 15–20 cm represents the optimal threshold for Mild AWD in rice production. This research provides a cultivation approach for synergistically producing high-yield, high-quality rice, which shows promising potential for scalable implementation.