Incorporating 30,000 kg ha−1 green manure with 15 % nitrogen reduction can enhance wheat quality by optimizing nitrogen translocation and sucrose metabolism

Green manure (GM) incorporation combined with nitrogen reduction can promote crop quality improvement. However, the mechanisms by which GM incorporation combined with nitrogen reduction enhances crop quality remain unclear. This study aimed to investigate the effects of GM incorporation amount combined with nitrogen reduction amount on wheat grain protein (GP) and starch (GS) content, and their mechanisms. A field experiment was carried out in an arid oasis region in northwestern China from 2022 to 2023. The seven treatments were as follows: (i) no GM incorporation + conventional nitrogen application (N 100 ), (ii) 15,000 kg ha −1 GM incorporation + 15 % nitrogen reduction (G 1 N 85 ), (iii) 22,500 kg ha −1 GM incorporation + 15 % nitrogen reduction (G 2 N 85 ), (iv) 30,000 kg ha −1 GM incorporation + 15 % nitrogen reduction (G 3 N 85 ), (v) 15,000 kg ha −1 GM incorporation + 30 % nitrogen reduction (G 1 N 70 ), (vi) 22,500 kg ha −1 GM incorporation + 30 % nitrogen reduction (G 2 N 70 ) (T), (vii) 30,000 kg ha −1 GM incorporation + 30 % nitrogen reduction (G 3 N 70 ). Results showed that compared with N 100 , all GM incorporation amount combined with nitrogen reduction amount treatments significantly increased wheat grain yield (GY), nitrogen use efficiency (NUE), GP and GS. Among them, G 3 N 85 exhibited the greatest improvements, enhancing GY by 26.5 %–42.6 %, NUE by 15.4 %–28.9 %, GP by 10.3 %–14.9 %, and GS by 8.1 %–15.5 %. In addition, compared with N 100 , the GM incorporation amount combined with nitrogen reduction amount treatments increased soil organic carbon (SOC) and soil mineral nitrogen (SMN), optimized wheat root biomass (RB), flag leaf net photosynthetic rate (P n ), transpiration rate (T r ), and promoted the nitrogen transport and distribution in various organs of wheat, enhancing sucrose phosphate synthase (SPS) activity, sucrose synthase (SS) activity, sucrose content, grain amylopectin content, and amylose content, with G 3 N 85 showing the most significant effects. Structural equation modeling revealed that an increase in wheat RB promoted T r and activated SS, thereby enhancing GS through the direct synthesis of amylose and sucrose-dependent amylopectin. The increase in GP was attributed to enhanced nitrogen translocation from vegetative organs to the grains and the subsequent rise in grain nitrogen content. Therefore, under the G 3 N 85 treatment, wheat yield can be maintained while simultaneously increasing GP and GS content, making it the optimal approach for combining GM incorporation with nitrogen reduction in arid oasis irrigation areas. • The mechanism of increasing the GS and GP of wheat grains was explored. • The GM incorporation amount for improving wheat quality has been determined. • G 3 N 85 increased GP by enhancing nitrogen translocation to grains. • G 3 N 85 enhances wheat GS content by promoting amylose and amylopectin content.