Abstract The adverse conditions of highly saline-sodic soils can impede straw decomposition, making straw-derived biochar a viable alternative to direct straw return. However, its specific pathways and comparative advantages over direct straw return in alleviating stress, improving nitrogen use efficiency, and increasing yield remain unclear. A field experiment was carried out over the period of 2023–2024 to investigate the impacts of straw management (CK: straw removal; SR: direct rice straw return; BR: rice straw-derived biochar return) and nitrogen levels (N0: 0, NL: 125, NM: 225, NH: 325 kg N ha −1 ) on rice stress physiology, nitrogen use efficiency, and yield in saline-sodic paddy fields. The results showed that both SR and BR significantly reduced leaf Na⁺ concentration, Na⁺/K⁺ ratio, and oxidative stress markers (MDA, H 2 O 2 , and O 2 − ), while concurrently increasing K⁺ concentration, soluble protein and proline contents, and the activities of antioxidant enzymes (SOD and CAT). Notably, the regulatory effect was significantly more pronounced for the BR than for the SR across the measured parameters. Moreover, both straw return practices significantly upregulated key nitrogen metabolism genes ( OsNR1, OsNRT1;1, OsNRT2;1, OsGS1;1, OsGS2, OsGDH2, OsFd-GOGAT ) and enhanced the activities of nitrate reductase (by 13.75–28.55%), glutamine synthetase (by 7.01–16.04%), and glutamate synthase (by 14.37–24.67%), thus improving nitrogen transport efficiency. Furthermore, compared to CK, the average total nitrogen accumulation and nitrogen use efficiency increased by 22.44–39.58% and 16.49–22.07%, respectively, under the BR, and by 12.39–49.84% and 11.60–23.18%, respectively, under the SR. Grain yield under BR was significantly higher by 4.04% and 16.25% compared to SR and CK, respectively. It is noteworthy that a significant yield difference between SR and CK was observed only in the second year, with no such difference detected in the first year. Structural equation modeling analysis further confirmed that the dominant effect of BR was mediated through a sequential causal pathway: from the amelioration of stress physiology to the enhancement of nitrogen metabolism, leading to improved nitrogen efficiency and ultimately elevated grain yield. Both the direct and indirect effects of BR were significantly stronger than those of SR. In conclusion, the combination of straw-derived biochar and 225 kg ha −1 nitrogen proved to be a more effective strategy than direct straw return for mitigating saline-alkali stress, boosting nitrogen use efficiency, and increasing grain yield in saline-sodic paddy soils.
Jin et al. (Mon,) studied this question.