Synergistic regulation mechanism of N in sugarcane-soil systems through 15N tracer and ecological stoichiometry

Sugarcane is a vital sugar crop in China. Low nitrogen use efficiency (NUE) is a key constraint to the sustainable development of the industry. To comprehensively evaluate the regulatory effects of N management on the sugarcane-soil system and its nutrient coordination, a controlled pot experiment was carried out using the Guitang 46 sugarcane variety in Baise, Guangxi. Six N treatment strategies were implemented: no N input (control), split applications at low, medium, and high levels, and one-time applications at medium and high levels. A combination of conventional agronomic measurements, 15 N isotope tracing, and ecological stoichiometry analysis was employed to investigate the influence of these treatments on (i) sugarcane growth (biomass accumulation, N uptake and allocation), (ii) soil properties (physicochemical characteristics), and (iii) system-level nutrient balance (C:N:P stoichiometric relationships within the plant–soil system).The findings revealed that the medium one-time N application delivered the most favorable outcomes. Specifically, it enhanced stem dry matter production (327.75 g) and total plant N uptake (4.79 g/plant) by 42.87% and 62.37%, respectively, compared to the control. Furthermore, it achieved a 15 N recovery rate of 40.78% and minimized N losses to just 20.66%. This treatment also contributed to an optimal stoichiometric balance—reflected in a stem C:N ratio of 28.5, a new leaf N:P ratio of 14.2, and a soil C:N ratio of 18.7, closely aligning with the ideal microbial decomposition threshold. Additionally, this approach significantly improved soil organic matter (OM, 63.97 g/kg), increased available N, and sustained stable invertase and urease enzyme activity. Taken together, these results demonstrate that a medium one-time N application simultaneously promotes high sugarcane yield, efficient N utilization, enhanced soil quality, and nutrient balance within the crop-soil system. These findings provide robust scientific support for reducing fertilizer input while maintaining productivity in sugarcane cultivation.