| Flue-cured tobacco is one of the most important cash crops in China. Ecological condition is the important factor for flue-cured tobacco formation because it determines the tobacco-style feature and quality. In Chongqing, the flue-cured tobacco areas are mainly located in mountainous regions. The complicated topography results in differences in ecological factors, such as climate and soil. Therefore, it is necessary to investigate the distribution of ecological factors, such as climate, soil, and topography, and to further analyze the effects of these factors on quality of flue-cured tobacco. In the current study, maps of land use (1:10000), acquisition data of flue-cured tobacco in recent years, long-term daily climate observations from212stations (1983-2012) and samples from soil testing and formulated fertilization of flue-cured tobacco planting areas were collected and analyzed. The effects of soil nutrients, climate and altitude on yield, average price, and ratio of high and middle quality of flue-cured tobacco were investigated using model prediction, clustering, classification and regression tree (CART) and correlation analyses. Meanwhile, the relationships between ecological factors and flue-cured tobacco smoking quality (aroma quality, aroma quantity, aftertaste, impurity, irritation and total score) were explored. And the relative importance of the factors to flue-cured tobacco yield and quality was also presented. The main conclusions were as follows.(1) On the basis of performance evaluation, IDW and kriging interpolation methods were employed to predict soil nutrients spatial distribution. The best model was IDW for soil available nitrogen. The best methods were spherical semi-variance model for pH and available phosphorus, Gaussian semi-variance model for organic matter, and linear semi-variance model for available potassium, respectively.The total area of flue-cured tobacco in Chongqing was642757mu in2012. Soil pH mostly ranged between5.5and6.5and between6.5and7.5, accounting for57.58%and27.16%of the total flue-cured tobacco planting areas, respectively. Organic matter mainly varied between20and30g/kg and between10and20g/kg, accounting for66.1%and17.51%of the total flue-cured tobacco planting areas, respectively. Available nitrogen changed between120and150mg/kg and between90and120mg/kg, accounting for40.22%and37.85%of the total flue-cured tobacco planting areas, respectively. Available phosphorus ranged between10and20mg/kg and between20and40mg/kg, accounting for59.73%and32.54%of the total flue-cured tobacco planting areas, respectively. Available potassium varied between100and150mg/kg and between50and100 mg/kg, accounting for46.59%and35.87%of the total flue-cured tobacco planting areas, respectively.Yield, average price and ratio of high and middle quality of flue-cured tobacco varied with soil nutrients. The highest values of yield, average price and ratio of high and middle quality of flue-cured tobacco were found in the areas with soil pH of6.5-7.5, available nitrogen of90-120mg/kg, available phosphorus of5-10mg/kg. Yield, average price, and ratio of high and middle quality of flue-cured tobacco increased with increasing of soil organic matter and available potassium.(2) Four climate types of flue-cured tobacco planting areas were identified using clustering analysis based on average temperature, sunshine hours, rainfall, total accumulated temperature of annual period and growing stage in fields. Cluster1was located in Shizhu, Nanchuan, Pengshui and Wulong and characterized by moderate temperature and rainfall and few sunshine hours. Cluster2was situated in Fengdu, Fuling, Wanzhou, and Wushan and characterized by high temperature and sunshine hours and moderate rainfall. Cluster3was located in Fengjie and Wuxi and characterized by high temperature and moderate rainfall and sunshine hours. Cluster4was situated in Youyang and Qianjiang and characterized by low temperature, less sunshine hours and higher amount of rainfall.The rank order of yield, average price, and ratio of high and middle quality of flue-cured tobacco was cluster2> cluster1> cluster3> cluster4. The results of analysis of variance showed that clusters1-3have significant higher yield and ratio of high and middle quality of flue-cured tobacco than that of cluster4. No significant difference was found in average prices between the clusters.(3) The altitude of flue-cured tobacco planting areas was divided into six groups:<600m,600-800m,800-1000m,1000-1200m,1200-1400m, and>1400m. From2009to2012, the proportions of flue-cured tobacco planting areas above the elevation of1000m were57.41%,57.74%,61.41%and64.09%, respectively. This indicated that the tobacco planting areas of Chongqing has a tendency to transfer to high altitude areas. Comparative study showed that yield of flue-cured tobacco increased with altitude. Average yield of flue-cured tobacco produced by the area of altitude above1000m was9.73%higher than that of other areas. Meanwhile, average price and ratio of high and middle quality of flue-cured tobacco increased with altitude in the study area.(4) The relative importance of ecological factors differed with yield, average price and ratio of high and middle quality of flue-cured tobacco. Here, climate indicators during the growing stage in fields were considered. For yield, the rank order of the factors was organic matter> available potassium> minimum temperature> elevation> available nitrogen> average temperature> maximum temperature> rainfall> sunshine hours> available phosphorus> pH. For average price, the rank order was sunshine hours> available nitrogen> available phosphorus> rainfall> pH> average temperature> organic matter> maximum temperature> available potassium> elevation> minimum temperature. For ratio of high and middle quality, the rank order was sunshine hours> rainfall> available nitrogen> elevation> minimum temperature> average temperature> pH> maximum temperature> organic matter> available phosphorus> available potassium. In general, the relative importance of climate, soil and topography varied with the studied indicators of flue-cured tobacco. For yield, the ecological factors was in order of soil nutrients> topography> climate indicators, for average price was climate indicators> soil nutrients> topography, for ratio of high and middle quality was climate indicators> topography> soil nutrients.(5) Different correlations were found between ecological factors and smoking quality of flue-cured tobacco. Soil organic matter was significantly positively correlated with aroma quality, aftertaste, impurity, irritation and total score. Soil available nitrogen and available phosphorus was significantly positively correlated with irritation. Soil available potassium was significantly positively correlated with aroma quality and irritation. Climate indicators during the growing stage in fields were considered. Rainfall had significant negative correlations with the studied smoking quality indicators. Sunshine hours showed significant positive correlations with aroma quality, aroma quantity, aftertaste, impurity. Altitude presented significant positive correlations with aroma quality, aroma quantity, impurity, total score, and a negative correlation with aftertaste.According to k-means and smoking quality indicators (aroma quality, aroma quantity, aftertaste, impurity and total score), smoking quality of flue-cured tobacco was classified into three groups with high, medium and low clusters. Then the obtained clusters and ecological factors were used as dependent and independent variables for CART model. The relative importance of ecological factors to smoking quality of flue-cured tobacco was obtained by the model. The rank order was average temperature> maximum temperature> minimum temperature> elevation> sunshine hours> rainfall> organic matter> available nitrogen> available phosphorus> pH> available potassium. In general, climate indicators followed by altitude and soil nutrients were the most important factors affecting the smoking quality of flue-cured tobacco. |
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