Stability Analysis of Chemical Quality of Tobacco Leaves in Honghe Prefecture of Yunnan Province

. To comprehensively analyze the stability of the chemical quality of tobacco leaf in Honghe State, and to provide a basis for finding ways to narrow the difference between tobacco leaf quality in Honghe State and maintaining the stability of the quality of tobacco leaves in the tobacco producing area. Statistics were used to analyze the annual stability of Honghe tobacco leaves and the stability of the tobacco planting range from 2014 to 2017. The chemical quality of Honghe tobacco leaves was not stable in different years, the total sugar and reduced sugar content showed the trend of decreasing year by year, in addition, the potassium and chlorine content of the tobacco leaves in this tobacco planting area had been at a low level for four consecutive years. In 2014 - 2017, the total sugar, reduced sugar and chlorine content of the tobacco leaves in Honghe State were all relatively small, while the variation coefficient values of nicotine and potassium content in tobacco leaves were large, while the chlorine content in tobacco leaves was extremely unstable between years. For four consecutive years, the chemical quality of tobacco leaves in seven tobacco - planting counties and cities in Honghe State was significant. The chemical quality of tobacco leaves in Honghe State was unstable between different counties and cities.


Introduction
The quality of tobacco leaves is closely related to the quality of cigarettes, and its quality characteristics directly affect the final quality of cigarette products [1] . Because the growth of tobacco leaves is affected by many factors such as ecological environment, soil, cultivation methods [2] , the instability of physical, chemical and biological characteristics of tobacco leaves [3] , which has a serious impact on the uniformity of tobacco quality. At present, the tobacco market is increasingly pursuing the stability and homogeneity of tobacco leaves [4] . The stable quality of raw materials has become an important factor to maintain the quality of tobacco leaves, especially the chemical stability of tobacco leaves, which directly determines the smoke characteristics of tobacco leaves and the availability of industrial production [5] . It has become the main reason to ensure the market value of middle and high-end tobacco brands. In the existing studies, the stability of tobacco leaves in Deyang [6] , Yunnan's main tobacco producing areas [1,7] , Lichuan [8] , Wenshan [9] , Hengyang [10] , Zunyi [11] , Panzhihua [5] were analyzed, and it was found that the quality of tobacco leaves in the same tobacco growing area varied between years. It can be seen that the instability of tobacco leaf quality has become an obvious problem in tobacco growing areas in China. Honghe Prefecture, located in the southeast of Yunnan Province, has unique natural conditions for flue-cured tobacco production, and is an excellent flue-cured tobacco production area in Yunnan Province. Because the ecological environment, soil fertility and cultivation conditions of tobacco growing areas in Honghe counties and cities are different, the comprehensive quality of tobacco leaves is also different [12] . At present, there are few studies on the stability of Yunnan Honghe tobacco leaves. The author intends to analyze the chemical properties of tobacco in Honghe Prefecture from 2014 to 2017, focusing on the differences between years and tobacco growing areas, and comprehensively evaluate the stability and changing trend of chemical quality of tobacco leaves in Honghe Prefecture, so as to provide a basis for finding ways to reduce the differences of tobacco quality in Honghe Prefecture and maintaining the stability of tobacco quality in this tobacco growing area.

Sample Collection
From 2014 to 2017, tobacco leaves were sampled from the main tobacco areas of Honghe Prefecture (Gejiu, Jianshui, Kaiyuan, Luxi, Mengzi, Mile and Shiping). The main tobacco varieties were K326, Hongda and Yun87. Sampling information of counties and municipalities in different years is shown in Table 1, of which the largest number is in 2017, followed by 2014, and similar in 2015 and 2016.

Determination of Chemical Index of Tobacco Leaf
The chemical composition of tobacco leaves was detected by Honghe Cigarette Factory of Honghe Hongyun Group Co., Ltd. The contents of total sugar, reducing sugar, nicotine, chloride ion, leaf nitrogen and leaf potassium in tobacco leaves were determined respectively.

Statistical Analysis
Data were analyzed by Excel and SPSS 19.0 software.

Difference analysis of conventional chemical indicators of tobacco leaves in different years in Honghe Prefecture
According to the analysis results of routine chemical indexes of tobacco leaves in different years in Honghe Prefecture (Table 2) Overall, the chemical quality of tobacco leaves in Honghe Prefecture was unstable, and the contents of total sugar and reducing sugar decreased year by year. In addition, the contents of potassium and chloride ions in tobacco leaves in Honghe Prefecture were at a low level for four consecutive years, which resulted in poor combustibility, weak elasticity and fragile tobacco leaves.

Variation coefficient analysis of conventional chemical indicators of tobacco leaves in different years in Honghe Prefecture
By calculating the coefficient of variation of conventional chemical indexes of tobacco leaves in different years, the dispersion degree of chemical components in different years can be analyzed. The specific results are shown in Table 3. The variation coefficients of total sugar, reducing sugar and nitrogen content of tobacco leaves in Honghe prefecture were small, and the variation coefficients of each index had little difference for four consecutive years, which indicated that the contents of three indexes in Honghe prefecture were relatively stable; the variation coefficients of nicotine and leaf potassium content in Honghe prefecture were relatively large, and the variation values of potassium content in tobacco leaves were relatively stable for four consecutive years. However, the variation of nicotine among years is quite different. The dispersion of chlorine content in tobacco leaves in Honghe Prefecture is very high, which indicates that the chlorine content in tobacco leaves in the tobacco area is extremely unstable. How to stabilize the chloride ion content in tobacco leaves in this tobacco area is an urgent problem to be solved.

Difference analysis of conventional chemical indicators of tobacco leaves in different counties and cities of Honghe Prefecture in 2014
From the comparison of routine chemical indexes of tobacco leaves in different counties and cities in Honghe Prefecture in 2014, it can be seen that the contents of total sugar, reducing sugar, nicotine, leaf potassium, leaf chlorine and leaf nitrogen in seven counties and cities in this year were significantly different (P < 0.05). Specific analysis of each index: the total sugar content of different counties and cities is significantly different, showing the size: Luxi, Mile > Mengzi, Shiping > Jianshui > Gejiu > Kaiyuan; the difference of reducing sugar content and total sugar results is not uniform, the index size of seven counties and cities is: Shiping > Mile, Mengzi > Luxi > Gejiu, Jianshui > Kaiyuan; Nicotine results can be used. It can be seen that the nicotine results in seven counties are relatively stable, among which Shiping and Jianshui are the highest, Gejiu and Kaiyuan are the second, Luxi, Mengzi and Mile are the lowest; the difference of potassium in tobacco leaves in seven counties and cities is also obvious, showing the size as follows: Gejiu > Shiping > Jianshui, Kaiyuan, Mengzi > Mile > Luxi. Water content is the highest, significantly higher than other counties and cities, Gejiu and Mengzi are the lowest; leaf nitrogen content is relatively stable in different counties and cities, among which Gejiu, Jianshui, Kaiyuan and Shiping are the highest, Mengzi is the second, Luxi and Mile are the lowest.

Difference analysis of conventional chemical indicators of tobacco leaves in different counties and cities of Honghe Prefecture in 2015
From In this year, leaf nitrogen content in different counties and cities of Honghe Prefecture could also be divided into two levels, among which Kaiyuan, Shiping and Jianshui were the highest, significantly higher than other counties and cities.

Difference analysis of conventional chemical indicators of tobacco leaves in different counties and cities of Honghe Prefecture in 2016
The results of routine chemical index analysis of tobacco leaves in different counties and cities of Honghe Prefecture in 2016 are shown in Table 6. It can be seen that the contents of total sugar, reducing sugar, leaf potassium and leaf chlorine in tobacco leaves of seven counties and cities in this year were significantly different, and reach significant levels (P < 0.05), while the contents of nicotine and leaf nitrogen were not significantly different. Specific analysis: In 2016, the total sugar content of tobacco leaves in seven counties and cities in Honghe Prefecture was significantly different, among which Mengzi and Mile had the highest content, Gejiu, Kaiyuan, Luxi and Shiping had the lowest, Jianshui, Mile and Shiping had the highest content, Jianshui, Kaiyuan, Mengzi had the second and Luxi had the lowest. The potassium content of tobacco leaves in different counties and cities of Honghe Prefecture in 2016 can be divided into two levels: Luxi is lower than other counties and cities, but there was no significant difference among other counties and cities. The chlorine content of tobacco leaves in Honghe Prefecture in 2016 can also be divided into two levels, among which Jianshui was the highest, which was significantly higher than other counties and cities, while there was no significant difference among other counties and cities.

Difference analysis of conventional chemical indicators of tobacco leaves in different counties and cities of Honghe Prefecture in 2016
The results of routine chemical index analysis of tobacco leaves in different counties and cities of Honghe Prefecture in 2016 are shown in Table 6. It can be seen that the contents of total sugar, reducing sugar, leaf potassium and leaf chlorine in tobacco leaves of seven counties and cities in this year were significantly different, and reach significant levels (P < 0.05), while the contents of nicotine and leaf nitrogen were not significantly different. Specific analysis: In 2016, the total sugar content of tobacco leaves in seven counties and cities in Honghe Prefecture was significantly different, among which Mengzi and Mile had the highest content, Gejiu, Kaiyuan, Luxi and Shiping had the lowest, Jianshui, Mile and Shiping had the highest content, Jianshui, Kaiyuan, Mengzi had the second and Luxi had the lowest. The potassium content of tobacco leaves in different counties and cities of Honghe Prefecture in 2016 can be divided into two levels: Luxi was lower than other counties and cities, but there was no significant difference among other counties and cities. The chlorine content of tobacco leaves in Honghe Prefecture in 2016 can also be divided into two levels, among which Jianshui was the highest, which was significantly higher than other counties and cities, while there was no significant difference among other counties and cities.

Difference analysis of conventional chemical indicators of tobacco leaves in different counties and cities of Honghe Prefecture in 2017
From the results of table 7, it can be seen that the contents of six chemical indicators of tobacco leaves in seven counties and cities of Honghe Prefecture in 2017 were significantly different, reaching significant levels (

Discussion
In tobacco cultivation, the final quality of tobacco leaves is closely related to varieties, climate, cultivation conditions and other factors. Under the influence of many factors, the chemical quality of tobacco leaves presents certain instability between years and regions. In actual production, the stability of tobacco quality has become an important factor in the stability of tobacco quality. How to maintain stability is a hot issue in tobacco cultivation. The results showed that the contents of total sugar, reducing sugar, nicotine, leaf potassium, leaf chlorine and leaf nitrogen of tobacco leaves in Honghe Prefecture for four consecutive years showed significant differences, which indicated that the chemical quality of tobacco leaves in Honghe Prefecture was unstable and fluctuated. Some researchers analyzed the annual stability of chemical components of tobacco leaves from major producing areas in China. The results showed that the stability of tobacco leaves in Liaoning Province was the worst, and that of Yulu was the best [13] . Zhao Lihong [1] analyzed the chemical stability of tobacco leaves in main tobacco -producing areas of Yunnan Province, and found that there were differences in chemical stability of tobacco leaves in different tobacco -producing areas, among which Wenshan had the worst stability and Dali had the best performance, but the stability of tobacco leaves in Honghe Prefecture was not thoroughly analyzed. The interannual stability of tobacco leaf quality in Yanshan [4] , Panzhihua [5] , Deyang [6] , Fenghuang [14] , Nanyang [15] was also reported in the literature. The results showed that the tobacco leaf in different tobacco areas had unstable problems in many chemical indexes. It can be seen that the instability of tobacco leaf quality has become a common problem. The specific investigation and analysis should be carried out in the target tobacco area to find out the instability factors so as to find the solution. This study found that the total sugar and reducing sugar content of tobacco leaves in Honghe Prefecture decreased year by year from 2004 to 2007. These two indicators are important indicators reflecting the good quality of tobacco leaves. Too high or too low will affect the quality of tobacco leaves. How to stabilize the total sugar and reducing sugar content of Honghe tobacco leaves should be emphasized in Honghe tobacco cultivation. This study also found that the potassium content of tobacco leaves in Honghe Prefecture was low for four consecutive years. Tobacco is a potassiumloving crop. Potassium plays an important role in the growth and development of tobacco plants. The potassium content of tobacco leaves in China is generally low, but the potassium content of tobacco leaves in Honghe Prefecture is on the low side as a whole. In addition, this study confirmed that the chloride ion content in Hezhou tobacco leaves from 2014 to 2017 was at a low level, and the stability between years was very poor, which was consistent with the results of Zhang Wanru [16] and Wang Yueneng [4] . It can be seen that chloride ion content has become one of the main factors of chemical instability in tobacco leaves. Tobacco is a chloride sensitive crop. Tobacco leaves with high or low chloride ions will affect the quality of tobacco leaves. Too low chloride ions will lead to fragility and poor hygroscopicity of tobacco leaves. It is suggested that Honghe Prefecture should start with the regulation of soil nutrients and improvement of agronomic measures to regulate the chloride ion content of tobacco plants in a reasonable range and improve their stability.
From the comparative analysis of tobacco chemical indicators of different counties and cities in Honghe Prefecture from 2014 to 2017, it can be seen that there are significant differences in the conventional chemical indicators of tobacco leaves among seven counties and cities in 2014, 2015 and 2017, while there are significant differences in the other indicators except nicotine and nitrogen content of tobacco leaves in 2016. It can be seen that Honghe Prefecture has significant differences in tobacco chemical indicators. Chemistry of tobacco leaves is unstable in different counties and cities. There are differences in ecological conditions such as climate and soil [12] in different counties and cities of Honghe Prefecture, which may be the main reason for regional differences in tobacco leaf quality. Because the ecological environment can be changed by cultivation techniques in production, Honghe Prefecture can explore the cultivation techniques adapted to local conditions according to the characteristics of tobacco -growing soils and ecological environment in each county and city, reduce the differences between chemical indexes of tobacco leaves in different counties and cities, and comprehensively improve the stability of tobacco quality in Honghe Prefecture.