The determination of an optimal nitrogen (N) fertilization rate is critical for the sustainable large-scale cultivation of Cinnamomum camphora var. linaloolifera for essential oil production. Both suboptimal and excessive nitrogen inputs can adversely affect plant sustainable development and essential oil biosynthesis, underscoring the necessity of precise nutrient management. This study investigated the effects of five N application rates (0, 45, 90, 135, and 180 kg·hm⁻²) on vegetative growth, essential oil yield, and quality. Growth parameters, including plant height, basal diameter, specific leaf area (SLA), and essential oil yield and yield rate. Oil composition was characterized via gas chromatography–mass spectrometry (GC-MS). The application of 90 kg·hm⁻² N significantly enhanced plant height (74.31%), basal diameter (54.95%), SLA (20.91%), and biomass (181.8%) relative to the nitrogen-free control. Nitrogen uptake was concentrated in foliar tissues, accounting for 82.8% of total plant nitrogen accumulation. This fertilization rate also maximized essential oil yield (9.15 g·plant⁻¹) and yield rate (2.44%), reflecting increases of 178.9% and 24.49%, respectively. Linalool was the predominant oil constituent (89.84–91.81%), with its highest concentration observed at the 90 kg·hm⁻² treatment. At this rate, the relative abundance of oxygenated compounds increased by 0.97%, while hydrocarbon content decreased by 0.62%, indicating a qualitative improvement in oil composition. The findings reveal a threshold response to nitrogen input, wherein rates exceeding 90 kg·hm⁻² did not confer further benefits and may reduce efficiency. Collectively, these results suggest that a nitrogen application rate of 90 kg·hm⁻² optimally enhances vegetative growth, nitrogen assimilation, and both the quantitative and qualitative traits of essential oils in C. camphora var. linaloolifera.

To investigate the effects of nitrogen application timing on photosynthetic traits and essential oil yield of Cinnamomum camphora var. linalooliferum coppice stands, an experiment was conducted with different nitrogen allocation ratios at coppicing, topdressing in June and August using a constant nitrogen amount of 270 kg·ha⁻¹. Plant growth, photosynthetic traits, and total above-ground essential oil yield were measured dynamically. Nitrogen application timing significantly affected photosynthetic performance, biomass accumulation, and essential oil yield (p < 0.05), showing clear stage-specific responses. It was found that early growth favored higher basal nitrogen fertilization, whereas middle-to-late growth benefited from increased topdressing. Principal component analysis revealed strong coordination among photosynthesis, growth traits, and essential oil yield, with N5 closely associated with high essential oil yield per plant (TEOy_p), plant height (PH), leaf area index (LAI), relative chlorophyll value (SPAD), and biomass traits. Correlation analysis further confirmed the stage-specific regulatory effects of photosynthetic traits and plant growth on essential oil yield. Nitrogen fertilization at coppicing mainly enhanced photosynthetic efficiency to support essential oil formation, whereas topdressing promoted vegetative growth and biomass accumulation to exploit yield potential. These findings will provide theoretical support and practical guidance for efficient nitrogen management in high-yield cultivation.