Effect of basal nitrogen fertilization time on nitrogen fertilizer use in flue-cured tobacco

Flue-cured tobacco (FCT) is a nitrogen-sensitive plant with strict requirements for nitrogen (N). Reasonable application of N fertilizer not only favors N absorption and utilization as nutrient, but also improves tobacco leaf quality. A field experiment was carried out to determine the effects of basal N fertilization time (0 d, 15 d and 30 d before tobacco seedling transplant) on N use parameters by FCT plant in the main tobacco production area of Hubei Province. The results showed that dry matter accumulation (DMA) and N content in tobacco leaf and stem increased with earlier basal fertilization time. For basal fertilizer application times of 15 d and 30 d before seedling transplant, DMA/N content respectively increased by 16.4%/1.5% and 22.6%/8.7% in tobacco leaf and by 2.5%/13.4% and 12.7%/33.9% in tobacco stem. Basal fertilizer application time did not significantly (P > 0.05) influence N recovery efficiency. However, it significantly (P < 0.05) decreased agronomic N use efficiency by 35.2% and 37.4% and physiological N use efficiency by 35.4% and 41.6% respectively for basal fertilizer application times of 15 d and 30 d before seedling transplant. Furthermore, basal fertilization time was negatively correlated with agronomic N use efficiency, physiological N use efficiency and partial factor productivity of applied N. However, agronomic N use efficiency was positively correlated with physiological N use efficiency and partial factor productivity of applied N. Also physiological N use efficiency was positively correlated with partial factor productivity of applied N. In terms of N absorption and utilization and dry matter accumulation in tobacco leaf, it was advantageous to apply basal N fertilizer 15 d and 30 d before tobacco seedling transplant.