Nitrogen-mediated improvement of ionic homeostasis and antioxidant capacity enhances rice yield and nitrogen use efficiency under soda saline-alkali stress

Background The unique physicochemical properties of soda saline-alkali soils significantly reduce soil nitrogen availability and crop nitrogen use efficiency. While high-yield and high-efficiency cultivation practice offer a key strategy for the synergistic improvement of both crop productivity and resource use efficiency. However, the optimal nitrogen input rate for these practices remains to be determined. Methods Hence, a three-year field study was implemented with nitrogen fertilizer application rates ranging from 0 to 325 kg ha −1 (0, 125, 175, 225, 275, 325 kg ha −1 ) to assess their effects on ionic balance, stress physiology, nitrogen use efficiency, and grain yield in rice grown under soda saline-alkali soil conditions. Results The findings indicate that additional nitrogen fertilizer, particularly at 275 kg ha −1 within the high-yield and high-efficiency cultivation practice, significantly reduced the leaf Na + /K + ratio and levels of superoxide anion (O 2 − ) and malondialdehyde (MDA), while increasing K + concentration and enhancing the levels of soluble proteins and proline, as well as the activities of peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Conversely, leaf Na + concentration increased significantly with rising nitrogen application rates. Furthermore, supplementary nitrogen fertilizer significantly improved total nitrogen uptake, nitrogen use efficiency (NUE), and nitrogen agronomic efficiency (NAE) in rice, which can be attributed to markedly enhanced activities of key nitrogen metabolism enzymes. Consequently, grain yields under the N4 (275 kg ha −1 ), N5 (325 kg ha −1 ), N3 (225 kg ha −1 ), N2 (175 kg ha −1 ), and N1 (125 kg ha −1 ) treatments exhibited significant increases of 94.34%, 62.40%, 56.15%, 37.78%, and 24.01%, respectively, relative to the N0 control. These results demonstrate that, within the high-yield and high-efficiency cultivation practice, nitrogen fertilization at a rate of 275 kg ha −1 plays a crucial role in improving rice productivity and optimizing nitrogen use efficiency in soda saline-alkali paddy fields.