Optimal agronomic measures combined with biochar increased rice yield through enhancing nitrogen use efficiency in soda saline-alkali fields

Soda saline-alkali stress severely hampers rice growth, nitrogen use efficiency, and yield formation. Biochar addition has been recognized as a potential solution to mitigate the adverse effects of saline-alkali stress on crops. Similarly, optimal agronomic measures are known to optimize crop growth conditions and enhance yield formation and resource utilization efficiency. Despite this knowledge, there is limited understanding of the combined effects of optimizing agronomic measures and biochar addition on ionic accumulation, nitrogen use efficiency, and rice yield in soda saline-alkali paddy fields. In this study, a 3-year field experiment was undertaken to evaluate the combined effects of optimal agronomic measures and biochar application on rice physiological properties, nitrogen use efficiency, and yield under five agronomic treatments: zero-fertilizer control (CK), farmers’ practice (FP), high-yield and high-efficiency management (OPT1), super-high-yield management (OPT2), high-yield and high-efficiency management combined with biochar (OPT1+B), and super-high-yield management combined with biochar (OPT2+B). The results demonstrate that treatments of optimal agronomic practices combined with biochar application (OPT2+B and OPT1+B) effectively reduced leaf Na⁺ concentration, Na⁺/K⁺ ratio, abscisic acid (ABA) concentration, and malondialdehyde (MDA) concentration, while enhancing leaf K⁺ concentration, improving leaf water status, and reducing relative electrical leakage over three years. Furthermore, these combined treatments positively influenced the enzyme activities of nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), and leaf nitrogen content (LN), as well as SPAD values. Additionally, the average nitrogen agronomic use efficiency (AEn) increased by 154.71 %, 109.81 %, 50.67 %, and 32.60 % in OPT1+B, OPT2+B, OPT1, and OPT2, respectively, compared to FP, while nitrogen physiological use efficiency (PEn) decreased by 64.03 %, 58.56 %, 29.46 %, and 21.81 %. The average grain yield (GY) increased by 311.42 %, 302.86 %, 196.57 %, 178.86 %, and 133.72 % in OPT2+B, OPT1+B, OPT2, and OPT1, respectively, compared to FP. AEn exhibited positive correlations with K⁺, leaf water status (LWS), NR, GS, GOGAT, LN, SPAD, and GY. These findings will offer new insights into the sustainable development and utilization of soda saline-alkali lands.