Effects of different planting patterns on soil microbial community, yield and quality of flue-cured tobacco leaves

In order to study the effects of different tobacco planting patterns on soil microbial community, yield and quality of flue-cured tobacco, a field experiment including tobacco mono-cropping, green manure-tobacco with crop rotation, wheat inter-cropping and wheat-tobacco with crop-rotation was conducted in Gaoqiao Town, Yishui County, Shandong Province. The dynamics of soil microbial community in plowed layer (0-25cm) in 2009 was evaluated by using phospholipid fatty acids (PLFAs) profiles. The results showed that at green manure ploughing stage (April 22), the total PLFAs content was the lowest in wheat inter-cropping treatment. At resettling growth stage of tobacco (June 20), it was the highest in manure-tobacco with crop rotation treatment, which had significant differences with other treatments. But at budding stage and mature stage, there was no significant difference among all treatments. The PLFAs data of different soil microbial floras and the differences among treatments both varied from the sampling time, and no significant difference of fungi PLFAs was found in all treatments. The ratios of fungi to bacteria PLFAs and gram-positive bacteria to gram-negative bacteria PLFAs indicated that the total soil microbial community and bacteria community structure were both influenced by the planting pattern and growing season. Soil microbial community structure changed most obviously in the wheat-tobacco rotation treatment during the whole growing season. Moreover, principal component analyses (PCA) of different microbial PLFAs at maturity stage revealed that an obvious differentiation was found among the planting patterns, and soil microbial community structure changed little in wheat-tobacco rotation, but changed greatly in the manure-tobacco rotation treatment and wheat inter-cropping treatment compared with the tobacco mono-cropping treatment. Furthermore, the economic characters and chemical composition of flue-cured tobacco leaves were both affected by different tobacco planting patterns. The average price, output value and configuration structure of flue-cured tobacco leaf were all increased. The contents of total sugar and reducing sugar were both decreased, but the content of potassium of tobacco leaf increased significantly in the other three treatments compared with the tobacco mono-cropping treatment. The wheat inter-cropping treatment and wheat-tobacco rotation treatment were both considered as the better tobacco planting patterns according to their comprehensive benefits. These findings can help to understand the effects of tobacco cultivation on soil microbial environment, and provide a scientific basis for optimizing the tobacco planting pattern of northern China.