Effects Of Nitrogen On The Growth And Quality Of Flue-cured Tobacco

Higher nicotine concentration in upper leaves is one of main reasons that cause lower usability of tobacco leaves in Chinese present tobacco production. In 2002, Two field experiments were conducted at Fenggang and Jinsha of Guizhou province in order to understand the effects of nitrogen supply on tobacco production, dry matter, nitrogen accumulation in plant, the change of mineral nitrogen and nitrate concentration in petiole of the first spreading leave, and to study mineralization of soil nitrogen. At the same time, a 15N-Iabelled experiment was conducted to analyze how much nitrogen in plant derived from soil or fertilizer. Meanwhile, five tobacco farmers in each site were investigated to evaluate the basic condition of tobacco production and farmer's present practices. The main results wereas follows:At rates of 75 kg N/hm2, 97.5 kg N/hm2, 120 kg N/hm2 and 142.5 kg N/hm2, apparent nitrogen loss rates were 31.8 kg/hm2, 66.2 kg/hm2, 77.6 kg/hm2and 96.0 kg/hm2 at Fenggang and 24.8 kg/hm2, 36.1 kg/hm2, 41.2 kg/hm2 and 62.4 kg/hm2 at Jinsha, respectively. Tobacco production, dry matter production, nitrogen accumulation were no significant difference between nitrogen rates and the growth of plant was inhibited for much loss of fertilizer at Fenggang. But yield, dry matter production, nitrogen accumulation increased with nitrogen rates due to less loss of fertilizer nitrogen at Jinsha.During the plant growth, mineralization potential of soil nitrogen was 88.6 kg/hm2 at Fenggang and 37.2 kg/hm2 at Jinsha. At Fenggang, nitrogen mineralized could meet nitrogen uptake of plant, but plant must uptake most of fertilizer nitrogen for better growth at Jinsha. Especially after topping, almost all nitrogen taken up by plant could come from apparent mineralization nitrogen with 39.9 kg/hm2 at Fenggang. But at Jinsha, nitrogen taken up by plant after topping mainly came from fertilizer because of less apparent mineralization nitrogen with 4.9 kg/hm2. Sequence of influence of soil nitrogen on leaves of different stalk position was upper leaves>cutters> lower leaves. And nitrogen content of upper leaves were affected greater by soil nitrogen than cutters and lower leaves.So, one of main reasons of higher nicotine concentration of upper leaves was nitrogen concentrated in upper leaves for less dry matter production of upper leaves and greater potential of soil supplying nitrogen.The results of investigation of tobacco farmers showed that higher nicotine concentration of upper leaves was the main problem in farmers practice at Fenggang, which was explained by higher nitrogen fertilizer rate and organic matter concentration in soil. At Jinsha, however, the main reasons was that farmers emphasized the delayed topdressing.In conclusion, higher nitrogen rates, greater mineralization potential of soil nitrogen and delayed topdressing could bring greater potential of soil supplying nitrogen after topping and easily cause higher nicotine concentration in upper leaves of tobacco.