Nitrogen Use Efficiency of Base Fertilizer and Top Dressing in Flue-Cured Tobacco in Rainy Regions

A field experiment was conducted using tobacco (Nicotiana tobacum L.) cultivar K326 grown in random block design with three replications in three treatments by 15N isotopes tracer in Liuyang institute of Hunan in 2007. The traits associated with nitrogen use efficiency were investigated during different growth stages of flue-cured tobacco. The results showed that tobacco plant mainly absorbed nitrogen from fertilizers in root elongation and vigorous growth stages and from soil in maturing stage. Nitrogen uptake reduced from base fertilizer, but increased from top dressing with the increase of top dressing under the same fertilizer application amount. At the same time, nitrogen use efficiency rose for base fertilizer, but declined for top dressing. The utilization of top dressing was significantly higher than that of base fertilizer in different treatments at different growth stages. After harvesting of tobacco leaves, nitrogen residue in base fertilizer was less than that in top dressing with the increase of top dressing ratio, but the total nitrogen residue and loss decreased. So enhancing properly the ratio of top dressing can improve ni-trogen use efficiency of flue-cured tobacco in rainy regions.