Influences of Different Nitrogen Fertilizer Rates on Activities of Key Enzymes Involved in Carbon and Nitrogen Metabolism and Economic Characteristics of Tobacco

The flue-cured tobacco variety K326 was used as experiment materi al 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 and the proportion of superior tobacco leaves all increased first and then decreased.The activity of nitrate reductase and invertase in each treatment all reached maximum in 70 d and 50 d after transplanting,respectively,then they reduced gradually;amylase activity varied with a small range within 90 days after transplanting and had changed in a lager range beyond 90 days after transplanting.SPAD value and chlorophyll content of tobacco leaves showed an obvious linear relationship.In conclusion,the treatment applied with 105 kg/hm2 of nitrogen fertilizer had the best economic characteristics of tobacco,and it would promote the balance and transformation for carbon and nitrogen metabolism and the formation of economic characteristics of tobacco.