Effect of soil factors on quality and style of flue-cured tobacco in Qujing District, Yunnan Province

Aroma quality evaluation methods were used to classify flue-cured tobacco into three aroma groups ― fen, moderate and enriched flavors. Depending on aroma score range (4~5, 2~4 and 0~2), the fen-flavor flue-cured tobacco was further classified into prominent fen-flavor, moderate fen-flavor, and weak fen-flavor. The classification focused on the effect of soil factors on fen-flavor aroma quality of flue-cured tobacco, with the aim of establishing reliable reference for tobacco material utilization. Grey relational analysis (GRA) was used to analyze the relationship between aroma characteristics of fen-flavor flue-cured tobacco and soil factors. Among ecological factors, little work has been done on how soil influences the aroma and taste of tobacco leaf. To this end, 973 samples of soil and flue-cured leaf were sampled in tobacco-growing fields in nine counties in Qujing District, Yunnan Province. While the collected soil samples were tested for fertility index, the corresponding tobacco leaves were tested for chemical components and aroma/taste quality. The results showed that prominent fen-flavor flue-cured tobacco had good aroma quality including rich aroma volume, less offensive/irritating odor, moderately lasting flavor, and small taste concentration and physiological strength. Prominent fen-flavor flue-cured tobacco agglomeration ability, sweetness and softness were significantly higher than those of moderate and weak fen-flavor flue-cured tobacco. Also the differences in the characteristics of fen-flavor flue-cured tobaccos in different soil types were significant. The characteristics of fen-flavor flue-cured tobacco from red soils were the strongest, followed by that from rice soils. Fen-flavor scores of flue-cured tobaccos from both red and rice soils were significantly higher than those from alluvial soils, yellow earth and purple soils. Furthermore, there were no significant differences among flue-cured tobaccos from alluvial soils, yellow earth and purple soils. Available phosphorus and potassium contents of red soils were relatively high. In red soil, 76.33% of total samples characterized as prominent fen-flavor, the proportion of tobacco with weak fen-flavor characteristics was highest in alluvial soils. Soils with tobacco of prominent fen-flavor had suitable pH and comparatively low contents of organic matter, total nitrogen and alkaline hydrolytic nitrogen. However, they had significantly higher contents of total phosphorus and potassium, and available potassium and iron than those with tobacco of weak fen-flavor. GRA also showed that the highest relational degree of aroma was with total phosphorus content, followed by total nitrogen content. Implicitly, soil factors such as available iron, magnesium and potassium contents and alkali-hydrolysis nitrogen strongly affected aroma of flue-cured tobacco. Furthermore, there was a significant correlation between the strength of fen-flavor characteristics and flue-cured tobacco variety. Cultivars such as the “Yunyan 87” and “K326” used in the study had evidently higher scores than the others.