Effects of soil amendments on rhizosphere microbial number, soil enzyme activity and yield of continuous cropped American ginseng

The continuous cropping of medicinal plants often resulted in deterioration of plant growth, decrease of plant resistibility to adversity, serious occurrence of disease and pest injury, and reduction of yield and quality. Numerous studies had found continuous copping obstacle in American ginseng cultivation, which restricted the sustainable development of American ginseng production. To explore the feasible routes of suppressing the barriers of continuous cropping of American ginseng, the paper systematically studied soil chemical properties, enzymes activities, rhizosphere microbial community and yield of continuously copped American ginseng through a randomized block experiment. Three soil amendments hydrated lime, effective microorganisms (EM) and biogas slurry in three application rates respectively were used in the experiment. The results showed that low-concentration of hydrated lime, middle-concentration of EM and high-concentration of biogas slurry were the most favorable conditions for American ginseng yield. The numbers of main groups of soil microorganisms and urease activity were significantly decreased, while soil pH significantly increased under hydrated lime treatments. The numbers of main groups of soil microorganisms, soil organic matter and nutrients contents were significantly improved (P < 0.05), and urease and polyphenoloxidase activities increased under biogas slurry and EM treatments. Correlation analysis showed significantly positive correlation between number of soil bacteria and activities of sucrase and polyphenoloxidase (r=0.895^**, 0.808^**). The numbers of fungi and actinomycetes were significantly and positively correlated with invertase, urease and polyphenoloxidase activities (r=0.932^**, 0.769^**, 0.840^**; 0.837^**, 0.891^**, 0.797^**). Bacteria number and soil organic matter content were significantly correlative (r=0.863^**). The results indicated that rhizosphere soil microorganisms were closely correlated with soil chemical properties, enzymes activities in continuous cropping system of American ginseng. Soil amendments in proper concentrations provided appropriate anti-continuous-cropping soil environments for American ginseng pro-duction.