| Taking soybean rhizospheric soil as tested material, changes of rhizosphere microbial flora composition in different year were studied by traditional culture method and Biolog technology with PCR-DGGE technology in this article. The relationship between rhizosphere microbial flora composition and soil nutrient and soybean yield were discussed. Soybean continuous cropping barrier and the reason of reduction of output were analyzed. The results provided the basis for revealing the impact of soybean rhizosphere bacterial community structure diversity and the changing character in different year and soybean continuous reduction mechanism.Soil samples were collected from long-term positioning test area of continuous cropping soybean which was established in 1995 by institute of soil fertilizer and environment resources, HAAS.Rhizosphere soil bacteria, actinomyces and fungi three kind of microbe were measured at the mature stage of soybean. Results showed that cultured microbial flora aggregates were decreased, the number of bacterial flora was reduced, the quantity of fungal flora was increased, and actinomycete flora took on irregular fluctuation within a smaller quantity under the condition of continuous cropping soybean. The total amount of bacteria accounted for 72.09%～93.36%of the total cultured microbes. Compared with rotation, continuous cropping and alternate cropping 1 to 10 years, soybean rhizosphere bacteria levels decreased with 9.33%～57.76%, especially in 6th years, bacterial number reduced 1.11×106/g dry soil, proportion was 57.76%. Continuous cropping and alternate cropping soybean lto 6 years, the number of fungi increased significantly, which was higher than rotation (higher 43.78%～88.44%). Continuous cropping 12 years, aggregates of fungi have larger changes and was higher 88.52% than rotation. The total quantity change of actinomyces was not obvious, showed irregular changing state, alternate cropping soybean increased 17.80% than rotation, continuous cropping 12 years, actinomyces reduced 59.12%.The results of rhizosphere soil nutrient changes of continuous cropping soybean were showed as follows:compared with rotation, rhizosphere soil total nitrogen, potassium, available nitrogen, phosphorus, potassium, and pH value decreased with alternate cropping soybean. Soil available phosphorus and soil bacterial number was positively related significantly, correlation coefficient was 0.68, with the increase of the content of available phosphorus in soil, bacterial numbers corresponding to increase. There was negative correlation between rhizosphere bacteria numbers and soil total phosphorus, available potassium content, r=-0.53* and r= 0.59*respectively.Virous yield indexs were measured and effect of continous cropping on soybean yield was analyzed.The results showed that yield of soybean was decreased under continuous cropping. Compared with rotation, production of soybean was reduced in each treatment from alternate cropping to continuous cropping 9 years. Soybean production tend to irregular change by the continuous cropping years, it rises in successive years and then drops in a few years continuously, the reasons of that is not clear. Soybean yield in different year has very significant difference, the order is:CS10> Rotation>CS11> CS13>CS2> CS12> CS15> CS5> CS8>CS4>CS1> CS6> CS3>CS9>CS7.To analyze the impact of soybean rhizosphere bacterial community structure diversity, the results showed that continous cropping soybean cause to changes in rhizosphere bacterial community structure, and the similarity between treatments are less than 75%. In rotation and continous cropping soybean 9 year, there are two kinds of bacteria in rhizosphere, they have high similarity with false aeromonas, and whether they have the function of bio-control is needed to determine by experiments.The change of rhizosphere soil microbial biomass carbon during soybean growth period was similar to rotation through testing soil. Microbial biomass carbon was lower in soybean seedlings in the whole growth period, while it elevated in the florescence, return to a relative minimum value in podding, achieve to a relatively high position in maturity. The changes of rhizosphere soil microbial biomass carbon during different growth stage were similar among rotation, alternate cropping, and the content order was Rotation>CS1>CS2. At the stage of maturity, rhizosphere microbial biomass carbon and soybean production was significantly positive relation. |
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