To provide the theoretical basis for rational nitrogen (N) application and promoting high yield and high quality of foxtail millet (Setaria italica (L.) Beauv.), this study aimed to clarify the effects of different N application rates on plant N utilization characteristics, grain yield and grain quality of foxtail millet.

To investigate the effects of different N application levels on plant N accumulation, transfer and utilization characteristics, grain yield and its components, grain micronutrients content and pasting properties, a 2-year field experiment (2020-2021) was performed with different N fertilization application at four levels (0, 75, 120, and 150 kg·hm^-2, represented as N0, N75, N120, and N150, respectively) in the Qinxian County of Shanxi Province, located in the spring sowing region of China.

Compared with N0, N application increased panicle number per unit area at harvest, grain number per panicle and plant productivity of foxtail millet. N application also significantly enhanced N translocation and promoted the distribution of both dry matter and N in grains. As a consequence, an enhanced grain yield was obtained when subjected to N application. Further, among all treatments, the highest values of panicle number per unit area at harvest, grain number per panicle, both grain yield and biomass, harvest index, total N accumulation and N translocation efficiency were obtained when 75 kg·hm^-2 was supplied; compared with the values produced by N0, the increased rate reached 7.5%, 23.3%, 31.0%, 21.2%, 8.6%, 40.3% and 9.2% by N75, respectively. Compared with N0 treatment, the content of Fe, Zn, Ca, Mg and Se in foxtail millet grains under N75 treatment were increased by 37.3%, 43.6%, 56.0%, 30.5% and 16.9% at most, respectively. Excessive N application (N 150) decreased grain number, harvest index and N translocation efficiency compared with N75 treatment. More than 75 kg·hm^-2 application resulted in diminished N translocation efficiency, by 23.1% and 28.1%, in 2020 and 2021, respectively. The content of amylopectin and starch yield were also limited by excessive N. Over-use N fertilizer also significantly decreased final viscosity, setback and trough viscosity. Pearson correlation coefficients demonstrated a strong positive relationship between plant N accumulation and the content of Fe, Zn, Ca, Mg and Se in foxtail millet grains, and a significant negative relationship between plant N accumulation and the content of amylopectin, final viscosity and trough viscosity in foxtail millet grains.

The N application at 75-120 kg·hm^-2 could promoted the allocation of dry matter and N in grain, which was relative to the enhanced N transfer from vegetative organs to grains. Also the reasonable pasting properties and biofortification of beneficial trace elements of Fe, Zn, Ca, Mg and Se was produced by such N dose in this study area.