Identify The Phytotoxic Substances Of Continuously Cropping Rehmannia Glutinosa Libosch Obstacle

In the text, we finds many differences between continuously cropped Rehmannia glutinosa Libosch for two years and only cropped Rehmannia glutinosa Libosch for one year in different periods through the field experiment.We identify the phytotoxic substances in root exudates of Rehmannia glutinosa Libosch by GC-MS, the root exudates was collected with Amberlite XAD-4 resin. We examine the four phenolic acids content of the Rehmannia glutinosa Libosch rhizosphere soil by hplc. The main results are as follows:We find many differences between continuously cropped Rehmannia glutinosa Libosch for two years and only cropped Rehmannia glutinosa Libosch for one year in different periods. The leaf of cropped Rehmannia glutinosa Libosch for only one year is plump,the roots of it normally expands. The leaf of continuously cropped Rehmannia glutinosa Libosch for two years is weak,the roots of it doesnt expand.Chlorohphy II content of only cropped Rehmannia glutinosa Libosch for one year is higher than it of continuously cropped Rehmannia glutinosa Libosch for two years.We also find yields of continuously cropped Rehmannia glutinosa Libosch for two years reduces 83.1% than it of only cropped Rehmannia glutinosa Libosch for one year.The kinds of organic compound collected with resin change is very big. Organic compound of mainly increase are phenolic acids, for example P-hydrobenozic acid, vanillic acid, ferulic acid and vanillin acid. We finnd that the content of vanillic acid, ferulic acid and vanillin acid rises continuously,but the change of P-hydrobenozic acidcontent is very small by hplc. The content of ferulic acid,vanillic acid and vanillin acid in cropped soil are 36.5,1.85,7times of it in controlled soil respectly,but the content of P-hydrobenozic acid in cropped soil is only 0.94 times of it in controlled soil.