The flue-cured tobacco variety K326 was used as experiment material to study the influences of different nitrogen fertilizer rates (0, 63, 84, 105, 126, 147 kg/hm2) on the activities of nitrate reductase, amylase and invertase, the chlorophyll content and the economic characteristics of tobacco. The results showed that with the increase of nitrogen fertilizer rate, the activities of nitrate reductase, amylase and invertase in tobacco leaves gradually raised, the Chlorophyll content increased, and the yield, the output value, the average price...