Effects of Rotation and Continuous Cropping Systems on Quality of Tobacco and Soil Nutrients

In order to explicit the effect of rotational cropping and continuous cropping on tobacco quality and soil nutrients,a continuous 6-year field experiment was carried out.Yield,chemical composition contents and disease occurrence of tobacco and soil nitrogen,phosphorus and potassium were analyzed in two different cropping systems.The results showed that there were no significant differences in yield,chemical composition contents and disease occurrence of tobacco between tobacco-maize rotation system and continuous tobacco cropping system.However,annual variation coefficient of tobacco yield in continuous cropping system was significantly lower than that in rotation system.There were no significant changes in the organic matter content and the contents of total N,P,K after 6-year cultivation between rotation system and continuous cropping system.But the change of available N,P and K were varied with cropping patterns.Content of available N decreased slightly in continuous cropping system,but showed increased slightly in tobacco-maize rotation system.Change of available P and K were just contrary to that of available N,and content of available K even showed decreased significantly in tobacco-maize rotation system.After 6-year cultivation,available nutrient proportion in continuous cropping system was1∶0.12∶2.17,which is more closer to the suitable value,1∶0.55∶2.40,compared to that in rotation system.Therefore,not all rotational cropping is effective.Some rotation crops,particularly those with high fertilizer application,have no obvious effect on improving the proportion of soil nutrients and tobacco yield and quality.