Abstract: [Objective] This study aimed to investigate the effects of nitrogen application at different growth stages on the agronomic traits, yield, and nutritional quality of silage maize, and to identify the optimal nitrogen application strategy. [Methods] Under a uniform total topdressing nitrogen rate （300 kg/hm² of urea）, two silage maize cultivars, Dajingjiu 23 and Heyu 9566, were studied. Three nitrogen application treatments were set at different growth stages: N1, a one-time application at the jointing stage; N2, split application at the jointing and big bell stages in a 5:5 ratio; and N3, split application at the jointing, big bell, and silking stages in a 3.3:3.3:3.3 ratio. A no-nitrogen topdressing control （N0） was also included. Agronomic traits were measured at the jointing, big bell, silking, grain filling, milk, and dough stages, while yield and nutritional quality were assessed at the dough stage. Grey relational analysis was employed to evaluate the overall performance of each treatment. [Results] The results showed that, compared with N0, the N3 treatment significantly （P<0.05） improved plant height, stem diameter, number of green leaves, and leaf area across all stages for both cultivars, with ear height at the dough stage also significantly increased. At the milk stage, Dajingjiu 23 under N3 had 4.2% and 1.5% higher plant height and 8.4% and 2.8% greater stem diameter compared with N1 and N2, respectively; Heyu 9566 under N3 showed 6.7% and 4.1% increases in plant height and 15.0% and 5.4% increases in stem diameter compared with N1 and N2, respectively, indicating that triple nitrogen topdressing promoted plant growth and lodging resistance. In terms of yield, both cultivars under N3 had significantly higher fresh and dry biomass than other treatments, with Dajingjiu 23 achieving 109.0 t/hm² fresh and 44.1 t/hm² dry yield, and Heyu 9566 reaching 133.8 t/hm² and 60.4 t/hm², suggesting that N3 facilitated biomass accumulation. In terms of nutritional quality, N3 resulted in relatively higher crude protein and starch contents, lower neutral detergent fiber （NDF） and acid detergent fiber （ADF） contents, and the highest relative feed value （RFV）, indicating improved forage digestibility and palatability. Grey relational analysis showed that both equal-weighted and weighted correlation rankings were consistent, with N3 achieving the highest score for both cultivars, confirming its optimal integrated effects on promoting growth, increasing yield, and improving nutritional quality. [Conclusion] The N3 treatment with three split nitrogen applications can simultaneously optimize the growth and development of silage corn, increase its biological yield, and improve its nutritional quality. It is the optimal nitrogen management scheme for the silage corn varieties Dajingjiu 23 and Heyu 9566, and can provide practical references for nitrogen regulation in the high-yield and high-quality production of silage corn.

Key words: silage maize, nitrogen fertilizer, agronomic traits, crop yield, nutritional quality, grey relational analysis