| In order to better understanding the problems of decisions on leaf ripeness, leaf harvest and curing control, the leaf maturity in major flue-cured tobacco varieties and the leaf characteristics in some new varieties introduced from foreign countries were studied under different ecological environments and fertilizer application conditions in Yunnan province. The main results were showed as follows:1. Results showed that the main effect factors of weather condition on curing technology were altitude, temperature, solar, raining and relative humidity. Four ecological areas including warm-cool, warm-warm, dry-hot, and wet-hot areas were partitioned based on the average values of these factors during tobacco field growth stages.2. Fresh leaf area, fresh leaf weight, dry weight, specific leaf weight, starch and sugar content were significant different among different ripeness leaves. Sugar content was increased along with leaf maturity, while the opponent trend was observed in starch content. Fresh leaf area, fresh leaf weight and dry weight of all stalk leaves in Yuxi city were higher than that Xuanwei city. Specific leaf weight of cutters and lugs for beginning ripeness was higher in Yuxi citythan that in Xuanwei city. Total sugar content and reductive sugar of fresh leaf were higher in Binchuan than that in ChuXiong. It was showed that starch and chlorine content were lower in Binchuan tobacco leaf than that in ChuXiong. For total nitrogen content, nicotine and protein of cutters and lugs, they were slight greater in Binchuan than that in ChuXiong, while the opponent trend was found in upper leaf.3. Along with ripeness improved, dry matter broke down, specific leaf weight and single leaf weight decreased. The highest leaf yield was observed in beginning ripeness, followed by optimum ripeness and over ripeness. Sugar and protein content decreased when leaf maturity improved. The best chemical components were found in optimum ripeness leaves. The optimum ripeness leaf demonstrated the best smoking quality, then beginning ripeness leaf, and over ripeness leaf. Leaf yield in Binchuan was higher than ChuXiong and Yuxi, but not product economic values. However, total sugar, reductive sugar, starch content were higher in those four ecological conditions than normal tobacco production area, which is not good indicator for tobacco quality.4. Significant differences in nitrosamine content were observed in different ripeness leaves. The greatest was existed for over ripeness leaf (63.5 ng/g), followed by beginning ripeness leaf (105.4 ng/g) and optimum ripeness leaf (84.5 ng/g). NAT plus NAB and total TSNA were highest in Yuxi city, then Mile county and Binchuan county, while NNK. showed significantly different trend. The highest NNN was found in Yuxi, followed by Binchuan, the lowest was existed for Mile.5. Leaf yield, rate of good grade, average price and economic value were higher at 7g N/plant and 8g N/plant rates than that at 5g N/plant and 6g N/plant application rates. The greatest leaf yield was produced in ChuXiong, while the highest economic value and average price were existed for Binchuan. Total sugar, reductive sugar and nicotine content were optimum in Xuanwei, and it's lower in starch content. However, total sugar, reductive sugar and starch content were too high in ChuXiong, nicotine content was low. Leaf smoking quality was better in both Binchuan and ChuXiong than other ecological areas.6. Leaf start to ripeness from low stalk to high stalk position 60 days after transplanting. Leaf ripeness improved when the angle between leaf and stem increased at the same fertilizer application rate. The angle between leaf and stem increased as fertilizer rate increased. Leaf ripeness was positively associated with the color changes of leaf midrib and branch rib. Leaf yellowing, leaf glandular trichome decreasing, leaf tipping and rolling were significantly different under different conditions, such as weather, fertilizer, nutrition supply. It's difficult to estimate if the leaf got to ripeness normally when drought and undernourishment appeared, though they seemed to possess the characteristics as normal leaf.
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