Nicotine accumulation and distribution in tobacco under continuous cropping

Continuous cropping of tobacco affects the growth and quality of flue-cured tobacco. This study investigated the effect of continuous tobacco cultivation on the accumulation and distribution of nicotine with aim of developing suitable cultivation methods. The study also discussed the theories and obstacles of continuous tobacco production. For that purpose, experiments were conducted in natural and fertilized soils with different periods (0, 3 and 5 years) of continuous cultivation in Yongsheng Town, Zhaozhou County, and the relationships among nicotine content, accumulation and distribution in flue-cured tobacco were analyzed. The results showed that nicotine gradually accumulated during the first 3~11 weeks after transplanting with the 3-year and 5-year continuous cropping under the natural fertility. After 11~17 weeks of transplanting, nicotine accumulated very rapidly in the 3-year and 5-year continuous cropping under the natural fertility. Nicotine accumulation for 0-year continuous cropped tobacco under the natural fertility was two weeks earlier, compared with that for the 3-year and 5-year continuous cropped tobacco. Nicotine accumulation was respectively 87.56 kg·hm^-2, 64.79 kg·hm^-2, 38.35 kg·hm^-2 under natural fertility, and 128.31 kg·hm^-2, 90.09 kg·hm^-2, 53.71 kg·hm^-2 under fertilization in the 0-year, 3-year and 5-year continuous cropped tobaccos at leaf harvest, approximately 17 weeks after transplanting. Continuous cultivation decreased nicotine adsorption and accumulation in both fertilized and natural soils. While nicotine distribution in roots and stems decreased with increasing period of continuous cropping, it increased in leaves with increasing period of continuous cropping in both natural and fertilized fields. The contents of nicotine in the continuous cropping systems were: 3-year > 5-year > 0-year, 3-year > 0-year > 5-year and 0-year > 3-year > 5-year in the lower, middle and upper leaves of tobacco, respectively. The nicotine content of leaves in different positions of plant of tobacco continuously cropped for 5 years was not up to the scratch of high quality tobacco. Continuous tobacco cultivation severely affected nicotine accumulation and distribution, and also the quality of flue-cured tobacco.