| With the rapid upgrading of the brand structure of cigarettes,the production and proportion of high-grade cigarettes are increasing significantly.This constantly stimulates demands for high-quality leaf tobacco and upgrades the demand structure.In order to alleviate the structural contradiction between leaf tobacco supply and demand and boost the leaf tobacco supply capacity of tobacco growing areas,most tobacco growing areas take the optimization of flue-cured tobacco grade structure as major work and the technology for optimization of flue-cured tobacco grade structure becomes a hot spot.Liangshan tobacco-growing area is one of the most suitable areas for the cultivation of flue-cured tobacco in China.With great advantages of natural resources,it develops rapidly in recent years and its leaf tobacco quality has been greatly improved,and its annual capacity of leaf tobacco production is 150 million kilograms.After implementation of the dual control policy of tobacco industry,its annual leaf tobacco production keeps above 135 million kilograms.Its fragrant characteristic is favored by backbone famous cigarette brands,and high-grade and high quality leaf tobacco is always in short supply.However,due to diverse terrain and landform and distinct vertical climate,the flue-cured tobacco production is still confronted with many problems such as poor maturity of the upper leaves,low grade structure,unreasonable position structure,and unbalanced regional structure.In high altitude tobacco growing areas such as mountain areas and flat dams with altitude above 1800 m,the flue-cured tobacco production is subject to drought in the early stage and low temperature in the late stage,is bad for optimizing structure.In order to optimize the flue-cured tobacco grade structure,improve the tobacco quality,and raise the supply level of leaf tobacco in Liangshan tobacco growing area,the research team studied the key technologies and mechanism of tobacco production on the basis of elements of tobacco production in Meiyu Town of Yanyuan County in Liangshan Yi Autonomous Prefecture in 2011-2014.Key technologies include "Screening of Varieties of Densely Planted Flue-cured Tobacco","Allocation of Climatic Resources for Flue-cured Tobacco Production","Structural Regulation for Flue-cured Tobacco Population","Regulation of Nitrogen Fertilizer Application amount and Remained Leaves",and "Removal of Unsuitable Tobacco Leaves".Through measuring the photosynthetic physiological indicators of fixed plants and fixed leaf position of each treatment,and measuring the plastid pigment,antioxidant enzyme activity,proline,and malondialdehyde of fresh leaf tobacco samples,the research team explored the physiological mechanism of tobacco maturity.Besides,through statistics of grade structure and economic traits of flue-cured tobacco,the research team measured chemical components of X2F,C3F and B2F samples,and evaluated the appearance quality and sensory quality.Finally,the research team screened technical measures for optimizing flue-cured tobacco grade structure and integrated key technologies of optimizing the flue-cured tobacco structure in high altitude tobacco growing areas.Main results are as follows:(1)In Yanyuan high altitude tobacco growing areas,at the early stage of flue-cured tobacco production,it often runs into drought,abundant heat and sunshine,the moderate temperature;at the late stage,the temperature drops rapidly and it is easy to suffer from low temperature,which is not favorable for maturity,harvesting,and curing of upper leaves.The transplanting period has a higher effect on climatic resource allocation at the early and late stages of flue-cured tobacco production.It mainly influences the temperature and relative humidity of air before rosette and influences the temperature of the maturity period.The early the transplantation,the lower the temperature and relative humidity of air,and the higher the temperature in the maturity period.If the transplantation is ahead of time,the growth period would get ahead of time and it will enter the maturity period earlier,activities of SOD,POD and CAT and the proline content will drop ahead of time,MDA content will rise ahead of time,the tobacco will enter the aging and mature physiological state earlier,and the maturity,harvesting and curing of upper leaves can be carried out ahead of time,which is favorable for avoiding low temperature at late stage of tobacco production.Besides,in case of the transplantation getting ahead of time,the tobacco plant will grow slowly at the early stage,the growth period will extend,which is favorable for accumulation of tobacco inclusions and aroma precursors,and improvement of the quality of tobacco leaves.However,too early transplantation may cause the field growth get vulnerable to climatic changes.Transplanting in April 8 to April 15,the proportion of high grade tobacco,average price,output,and output value of tobacco after baking were high,the score of evaluation of sensory quality of middle and upper leaves was high,so this period is the best transplantation period for Yanyuan high altitude tobacco growing area.(2)At transplanting density of 20800 plants/hm2,in the maturity period,the net photosynthetic rate of KRK26 and Yunyan 87 was the lowest,the stem-leaf angle and opening angle were the largest,and it became mature and yellow leaves fall at first.In ecological condition vulnerable to low temperature,in the maturity period of flue-cured tobacco in Yanyuan high altitude tobacco growing area,it had dominant advantage in upper leaf harvesting and curing.For KRK26 flue-cured tobacco:its ratio of middle leaves was 13.2?18.3%higher than other varieties,its output was 1.8?28.8%higher than other varieties,the proportion of high grade tobacco and average price was higher,the coordination of chemical components was excellent,the appearance and sensory quality was better,its harvestable leaves was the most,optimizimg structure could be highly adjusted,thus it can be developed moderately;for Yunyan 87:after curing,the highest proportion of high grade tobacco and average price,higher proportion and higher output value of middle leaves,best sensory quality,excellent coordination of chemical components and high appearance quality,many leaves harvestable,optimization structure highly adjustable,thus it can be developed energetically.For Honghuadajinyuan(Hongda),after curing,the upper leaves had high sensory quality,showing fragrant style.Hongda had prominent fragrant nature and fragrance volume,highly industrial application,thus can be further developed.However,due to poor economic traits,it is recommended to provide appropriate amount of subsidies for growers.(3)Under the condition of 20800 plants/hm2,"increasing the application amount of nitrogen fertilizer and reducing remained leaves" delayed the tobacco maturity period and the leaf antioxidant enzymes would down,the chlorophyll degradation rate would decrease,and the maturity and yellow leaves falling of the same position leaves delayed.Through increasing the application amount of nitrogen fertilizer,it could increase the tobacco leaf production and output value,but the score of proportion of middle tobacco leaves,the proportion of middle and high grade tobacco,and sensory quality of middle leaves firstly rose then declined,while the score of proportion of high grade tobacco and evaluation of sensory quality of upper leaves dropped;through reducing the number of remained leaves,the score of average price of tobacco,proportion of high grade tobacco,the proportion of middle and high grade tobacco,and evaluation of sensory quality of upper leaves firstly significantly increased then slightly dropped,the score of evaluation of sensory quality of upper leaves gradually increased,while the tobacco leaf production and output value dropped.In Yanyuan high altitude tobacco growing area,at transplanting density of 20800 piants/hm2,applying chemical pure nitrogen 90 kg/hm2 and keeping 16 leaves for a singleplant had the best economic traits and overall performance of structure of tobacco;main chemical components of tobacco leaves reflected the characteristics of the position and excellent coordination;the overall performance of sensory quality of tobacco leaves was the best.(4)The relationship between the lower leaf unfolding and plant shape building and the density was the largest;the lower the density,the larger and the more extension the lower leaf unfolding,the larger the contained angle and opening angle of stalk and leaf,the larger the body radius and drooping degree;there was a close relationship between middle and upper leaf unfolding and plant shape building and density,and the influence of number of remained leaves was also great;the less the number of remained leaves,the more balanced the sunlight of leaves in every position,and the greater the light energy utilization ratio,the more fully the accumulation of nutrients and photosynthetic products in the middle and upper leaves,the richer the tobacco inclusions,the greater the leaf unfolding in the maturity period,the faster the increase of leaf weight,and the greater the opening angle and drooping degree."Increasing the transplanting density and reducing the number of harvested and cured leaves" would delay the maturity and falling of the same part leaves,but the number of remained leaves decreased,and the top leaf position dropped,but it still can finish harvesting and curing ahead of time;"increasing the transplanting density and reducing the number of remained leaves" had a slightly adverse effect on the sensory quality of middle leaves,but had a significant effect on improving the sensory quality of upper leaves;for the treatment of few remained leaves,the sensory quality of upper leaves had the tendency of getting close to middle leaves;for Yanyuan high altitude tobacco growing area,it is preferred to adopt the transplanting mode of "wide spacing between rows and narrow spacing in the rows"(spacing in the rows and spacing between rows:1.2 m × 0.4-0.45 m),keep about 16 leaves for a single plant,and produce moderate size tobacco,to optimize the structure of flue-cured tobacco grade.(5)For the second removal of unsuitable tobacco leaves,in the maturity period,the decline rate of leaf antioxidant enzymes would slow down,and the chlorophyll degradation rate would decrease.Also,it would delay the maturity and yellow leaf falling of the same position,delay the second removal of leaves,and have weaker effect on the maturity and yellow leaf falling;the second removal of unsuitable fresh tobacco leaves would lead to drop of production and output value,but could increase the average price and proportion of high grade tobacco and middle leaves;compared with the control group,the second removal of 3 upper leaves increased the average price by 14.29%,increased the proportion of high quality tobacco by 10.01%,and increased the proportion of middle leaves by 12.46%,increased the score of sensory quality of upper leaves by 3.17 points;if the second removal of top leaf was delayed,the proportion of middle leaves would be higher and the proportion of high grade leaves discarded would be higher.In Yanyuan high altitude tobacco growing area,the effect of optimizing flue-cured tobacco structure would be better through the technical measure of removing one bottom leaf during topping and removing or discarding 3 top leaves in 15 days after topping.(6)It integrated key technical system of optimizing the grade structure of flue-cured tobacco in high altitude area suitable for climatic characteristics of high altitude tobacco growing area through "taking the variety selection as basis,moderately densely planting as the key,making overall plan for nitrogen fertilizer as the core,and reducing the number of remained leaves as the guarantee". |
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