[Characteristics of nitrogen accumulation and utilization in nitrogen-efficient rice under different ecological...

Clarifying nitrogen accumulation and utilization in nitrogen-efficient rice under different ecological conditions can provide a theoretical basis for breeding such rice varieties and optimizing fertilizer management. We conducted a two-factor split-plot field experiment under two contrasting light conditions: low-light and overcast conditions in Dayi, Sichuan, and sufficient-light conditions in Yongsheng, Yunnan. The main plot factor consisted of three nitrogen application levels: no nitrogen application (N₀), reduced nitrogen (120 kg·hm^-2, N₁₂₀), and conventional nitrogen (180 kg·hm^-2, N₁₈₀). The subplot factor included 10 rice varieties classified into three nitrogen efficiency types: low-nitrogen high-efficiency type, high-nitrogen high-efficiency type, and other type. We quantified nitrogen accumulation, allocation, translocation, and utilization characteristics by measuring plant dry matter weight and nitrogen content at the full heading and maturity stages. The results showed that nitrogen uptake, accumulation, and utilization in rice are jointly influenced by rice variety, nitrogen fertilizer level, and their interaction effect. Under the ecological conditions of Dayi, low-nitrogen high-efficiency rice performed optimally under the N₁₂₀ treatment, exhibiting the highest nitrogen content in various organs at maturity. Specifically, leaf nitrogen content was 68.8% higher than that of high-nitrogen high-efficiency rice and 6.8% higher than that of other type. Compared to other type, low-nitrogen high-efficiency rice showed increases of 27.3%-37.7% in pre-heading nitrogen accumulation in stem-sheaths and leaves, and 16.7%-44.4% in the contribution of pre-heading stem-sheath and leaf nitrogen to grains, ultimately leading to a 14.4%-18.9% increase in total nitrogen accumulation. In Yongsheng, high-nitrogen high-efficiency rice performed outstandingly under the N₁₈₀ treatment, with higher nitrogen content in various organs than other type, showing an average increase of 13.1% at the full heading stage and 8.5% at the maturity stage, respectively. At the maturity stage, nitrogen allocation to panicles increased by 5.2% compared to other type. The nitrogen translocation contribution rate of pre-heading leaves increased by 19.0%-27.5% compared to the other two rice types, ultimately raising total plant nitrogen accumulation by 13.3%-23.8%. In Dayi, the low-nitrogen high-efficiency rice, and in Yongsheng, the high-nitrogen high-efficiency rice, exhibited significantly higher nitrogen fertilizer partial productivity, nitrogen agronomic utilization efficiency, and nitrogen fertilizer recovery efficiency compared to other type. In summary, low-nitrogen high-efficiency rice combined with reduced nitrogen application (N₁₂₀) is suitable for regions with low-light and overcast conditions such as Dayi, while high-nitrogen high-efficiency rice combined with conventional nitrogen application (N₁₈₀) is applicable to regions with sufficient light and temperature like Yongsheng.