Studies On Soil Rhizosphere Effect Of Continuous Cropping Poplar Plantation

For the sake of keeping on sustainable forest management, resolving and revealing the problem of soil degradation, and exploring the feasibility of poplar plantation continuous cropping, measures and approach of site productivity,the soil rhizosphere effect of the forestlands of continuous cropping, different ages, intercropping and fertilizing were studied systemically from 2004 to 2007. Results showed that:1. The degree of soil degradation of alternative continuous cropping was below nonalter-continuous cropping,soil rhizosphere effect was declined gradually. Tree height, diameter at breast height and volume were declined. In rhizosphere and non–rhizosphere the content of soil organic matter, available P, and available K were gradually declined. The rhizosphere effect value of soil nutrients was beyond 1, the that of soil organic matter was increased, and soil available P, available K and available N were diminished as planting generation increased. The variation law of the activities of soil urease, alk-phosphatase and catalase in rhizosphere and non–rhizosphere was same, the activities gradually declined as planting generation increased, but polyphenol and peroxidase was opposite. The rhizosphere effect values of soil enzyme besides polyphenol were beyond 1, that of soil urease, alk-phosphatase and catalase were decreased, and that of polyphenol and peroxidase were enlarged as planting generation increased. The amount of actinomyces, cel-decomposing bacteria, nitrogen fixing bacteria and ammonificator in rhizosphere and non–rhizosphere were decreased, at the same time, configuration of soil microbes was also changed. Proportion of soil actinomyces, fungi, cel-decomposing bacteria in soil microbes were improved, and that nitrogen fixing bacteria and ammonificator were descended. The rhizosphere effect values of most soil microbes were beyond 1, which of soil actinomyces and fungi was enlarged, but that of cel-decomposing bacteria, nitrogen fixing bacteria, ammonificator and nitrosotying bacteria were reduced as the planting generation. There was the relation between phenolic acids and planting generation, the accumulation of phenolic acids was caused by continuous cropping, and that of 2rd generation forest was the biggest, the content of P-hydroxybenzonic acid was the highest, cinnamic acid was in the next place in total phenolic acids.2. In the forestland of different forest age, the rhizosphere effect of soil nutrients was the lowest, but that of soil enzyme and microbes the biggest in middle-age plantation. Content of soil organic matter, available K and available N were depressed at first, then elevated, but available P gradually declined. The rhizospere effect value of 3 age, 9age and 12age were beyond 1, but that of 6 age was below 1, the change of rhizospere effect of soil nutrient were raised after decreasing. Soil alk-phosphatase depressed at first, then elevated, soil urease in rhizosphere depressed at first, then elevated, but in non–rhizosphere gradually increased, peroxidase was as same as urease in non–rhizosphere, the activity of soil catalase had no change among both soils. The rhizospere effect value of catalase, urease, alk-phosphatase were beyond 1, rhizospere effect of alk-phosphatase had strong law of change as variation of the forest age, significantly bigger, others had no law, but in 3 and 6 age rhizospere effects were higher. Soil actinomyces, fungi in rhizosphere and non–rhizosphere depressed at first, and then elevated, cel-decomposing bacteria and ammonificator gradually declined, nitrogen fixing bacteria gradually increased. Rhizospere effect value of nitrogen fixing bacteria was below 1, others were beyond 1.3. Rhizospere effect was affected by intercropping. Rhizospere effect of soil nutrients was great impacted by intercropping with spearmint. After intercropping Rhizospere effect value of polyphenol, peroxidase and catalase were increased, but that of urease and alk-phosphatase were declined, that of soil microbes was affected, gradually declined. At the same time, activities of soil enzyme, amount of soil microbes and soil physical properties were improved by intercropping.4. The activities of soil enzyme and amount of soil microbes in rhizosphere and non–rhizosphere of fertilization were elevated greatly. Soil enzyme, microbes and rhizosphere effect were affected significantly by organic fertilization. Rhizosphere effect of organic fertilizer treatment was below 1.5. By analysis of the connection of soil microbes, soil enzyme and soil nutrients, the result was showed that the connection was significantly, the level of soil nutrient could be responsed by soil urease and alk-phosphatase, and revealed by soil actinomyces, fungi, nitrogen fixing bacterium and ammonificator.