The screening of N-efficient cultivars to reduce N fertigation rates and delay application timing presents effective strategies for mitigating the constraint of low N use efficiency in sustainable cotton production in arid regions. Five cotton cultivars (P1, P2, P3, P4 and P5) and three N fertigation strategies ((1) conventional N fertigation (N0, 360 kg N ha- 1, 2:6:2 in the bud stage, flower boll stage, and late boll stage); (2) reduced N fertigation (N1, 240 kg N ha- 1, 2:6:2); and (3) reduced and delayed N fertigation (N2, 240 kg N ha-1, 0:6:4)) were conducted in 2023 and 2024. N2P5 resulted in the highest seed cotton yield, which was primarily attributed to having the highest boll density. This was achieved through the establishment of a canopy structure with high light-use efficiency. Compared with the N0 and N1 treatments, the N2 treatment reduced the leaf area index (LAI) during the peak boll-setting period, thereby increasing light interception in the middle and lower canopy layers by 42.9-228.6 % and significantly improving the light conditions in these zones. This optimization not only increased the number of fruiting nodes in the middle and lower canopies but also promoted biomass accumulation in reproductive organs. Moreover, compared with the other cultivars, P5 increased single boll weight and boll density by 3.9-8.5 % and 1.8-17.5 %, respectively. Ultimately, the synergistic increase in boll density and single boll weight in the middle and lower canopies contributed to a 2.4-59.0 % increase in seed cotton yield in layers, thereby driving overall yield improvement. Therefore, selecting N-efficient cultivars and delaying limited N application optimized canopy structure and source-sink relationships, enhanced light utilization in middle and lower canopies and promoted photosynthate translocation to reproductive organs, thereby increasing harvestable boll number and yield. This strategy offers new insights for N management and cultivar selection in ecologically similar regions.