Abstract: Clarifying the influence of reduced nitrogen fertilization on nitrogen uptake and utilization of sugarcane organs can provide scientific basis for rational fertilization in sugarcane production. Based on ¹⁵N tracer technique, a micro-plot field experiment was conducted to investigate the effects of three application levels of nitrogen fertilizers \[low level (N300): urea 300 kg·hm^-2; middle level (N400): urea 400 kg·hm^-2; high level (N500, the conventional nitrogen application): urea 500 kg·hm^-2\] on nitrogen uptake and utilization of leaves, stems and roots, and residual nitrogen rate of soil (0-10, 10-20, 20-40 cm) after topdressing and at stages of seedling, extension, and mature, respectively. The results showed that reduced nitrogen fertilization did not affect the accumulation of ¹⁵N in leaves and stems at stages of extension and mature. Generally, accumulated N concentration, accumulated ¹⁵N concentration, amount of N derived from fertilizer and amount of N derived from soil of sugarcane root were higher in N500 treatment than that in the other treatments at stages of topdressing, seedling, extension, and mature. At the stages of seedling, extension and mature, N uptake and fertilizer use efficiency of leaf, stem and root were higher in the N300 treatment than that in the other treatments. There were no significant differences of accumulated ¹⁵N concentration of soil at 0-10, 10-20, 20-40 cm layers among the three N treatments at extension stage. The N residual rate of 0-10, 10-20, 20-40 cm soil was higher in the N300 treatment than that in the other treatments at stages of topdressing, seedling, extension and mature. Collectively, reduced nitrogen fertilization is beneficial to improving fertilizer use efficiency of roots and stems, and consequently the yield of sugarcane.

Key words: nitrogen fertilizer application level, sugarcane organ, nitrogen use efficiency, nitrogen residual rate, ¹⁵N tracer technique