Effect of Continuously Cropped Tobacco Soil on Growth,Development,Yield and Quality of Flue-cured Tobacco

Effects of continuously cropped tobacco soils on the growth,yield and quality of the flue-cured tobacco variety,HD,were studied with a field experiment at Xiangyun,Yunnan.The results showed that,as the cropping years increased,(1)the growth of the tobacco plants was retarded with prolonged growth periods and reduced agronomic traits;(2)the occurrence of tobacco diseases,such as black root rot,black shank,and root-knot nematode,became gradually serious;(3)the activities of tobacco nitrate reductase and catalase reduced;(4)the yield,output value,average price and high-to-middle-quality ratio of the flue-cured tobacco leaves decreased;(5)the contents and balance of the chemical composition of the cured leaves began to gradually deviated from the optimum values.At the same time,the quality of cured leaves deteriorated.It was concluded that,as the cropping years of the same tobacco field increased,the rate of nitrogen assimilation was reduced and the plant′s nitrogen metabolism imbalanced,while harmful substances accumulated.As a result,the plant chemistry was ill-affected,the growth stunned,the disease-and pest-resistance reduced,and the tobacco yield and quality lowered.