Effects of nitrogen fertilizer rates on nutrient uptake, vertical nutrient distribution, and nitrogen balance in...

Optimizing nitrogen (N) fertilizer management is essential for sustainable crop production in semi-arid, rain-fed agricultural regions. This study evaluated the effects of different N-fertilizer rates on nutrient uptake, soil nutrient distribution, and N balance in spring wheat (Triticum aestivum L.) under dryland conditions.

The analysis was based on a long-term field experiment initiated 2003 in Dingxi, Gansu Province, China, with five N application rates: 0, 52.5, 105.0, 157.5, and 210.0 kg N ha^-1 (designated as N1-N5).

The study results showed that the concentrations and accumulations of N and K in wheat organs increased significantly with increasing N rates. However, both yield and nutrient uptake plateaued at105 kg N ha^-1 (N3) and no statistically significant benefits were observed at higher N rates. In contrast, increasing N fertilization significantly reduced grain P concentration, with the N5 treatment showing a 17.80% decrease compared with N1. Soil nutrient responses exhibited clear vertical differentiation. Residual available N in the 0-100 cm soil layer increased significantly with increasing N rates, with a 32.20% increase under N5 compared with N1, whereas available P decreased by 31.49%. Available K showed redistribution characteristics, with the surface layer and enrichment in the subsoil. Nitrogen balance analysis indicated that the apparent N-use efficiency decreased from 95.12% to 39.71% as N rates increased, while the apparent loss rate shifted from negative to positive values, reaching 33.79% under N5. The N3 treatment achieved a near equilibrium N balance (8.69 kg ha^-1), whereas the N5 treatment resulted in a substantial N surplus of 102.34 kg ha^-1. Overall, an application rate of 105 kg N ha^-1 was identified as the optimal N fertilizer rate for dryland spring wheat.

This rate ensured adequate N uptake and grain yield, maintained high N use efficiency (NUE), minimized potential environmental risks, and achieved a balanced N supply-demand relationship.