Influences of nitrogen application rates on key enzyme activities of carbon-nitrogen metabolism and quality of dark sun-cured tobacco in Jiaohe

In order to solve the imbalance of carbon-nitrogen metabolism and quality deterioration of dark sun-cured tobacco leaves caused by inappropriate application of nitrogen fertilizer in Jiaohe tobacco-planting areas, the effects of different nitrogen rates on the key enzyme activities of carbon-nitrogen metabolism and quality of dark sun-cured tobacco (cv. Piaohe 1) were studied. The results showed that the activities of nitrate reductase, glutamine synthetase and sucrose invertase and the contents of chlorophyll and carotenoid in tobacco leaves were elevated by the increase of nitrogen application rate. With higher nitrogen application rates, the contents of nicotine and total nitrogen in cured leaves increased and sugar content decreased. The potassium content, aroma quality and quantity, and sensory quality score of tobacco leaves were the highest at the nitrogen application rate of 75.0-97.5 kg/hm². Based on the results of these two-year field experiments, the suitable nitrogen application rate for dark sun-cured tobacco was determined to be 75.0-97.5 kg/hm² in the dark brown soils with higher fertility in Jiaohe, Jilin Province.