Effects of continuous planting of poplars on soil biological activity and nutrients

The continuously planted poplar plantations in Dashahe Forest Farm,Fengxian county,Jiangsu province were chosen to study the characteristics of nutrients,soil enzymes and microorganisms in the rhizosphere and non-rhizosphere.Effects of continuous planting of poplars on the soil fertility of artificial forests were also discussed. The results showed as follows: 1 The content of soil nutrient,activity of soil enzymes( urease,invertase,alkaline phosphatase,catalase) and the number of microorganisms( fungi,actinomyces,bacteria) in the rhizosphere were higher than that in the non-rhizosphere,while soil pH value and the polyphenol oxidase activity showed the opposite appearance. 2 The enhancement of soil urease,invertase,alkaline phosphatase and catalase activity as well as the increasement of microorganisms were advantageous to the accumulation of soil organic matter and the transformation of nutrient elements. But the greater the activity of polyphenol oxidase was,the lower the content of soil nutrient was. The decline of soil pH value had an adverse effect on the most of the soil enzymes and microorganisms. The correlation between fungi and soil enzyme was closer than it between actinomyces and soil enzyme or bacteria and soil enzyme. 3 Because of the continuous cropping poplar,the rhizosphere soil pH was lower than non rhizosphere soil and continued to reducing with the number of cropping generations. But the polyphenol oxidase gradually increase with the contimous cropping,while the soil nutrients,urease,invertase and alkaline phosphatase,catalase and microorganisms gradually reduced even lower than non rhizosphere soil.In conclusion,continuous planting of poplars should be avoided at Fengxian. The replacement of varieties of poplar or species could be used to alleviate the negative influence of continuous planting. Maintaining the level of soil enzyme and microorganisms should be paid attention to,and measures were taken to decrease the soil acidification at the same time.