Researching On Soil Microbial Characteristics In Tobacco‐growing Soils Under Different Continuous Cropping Years

A pot and a filed experiment were carried out using K326 Flued-cured tobacco as the test plant to research the effect of continuous cropping system on the variation of soil microorganism and the activities of soil enzymes. The test soil was collected from the plowland of tobacco with 0,4,6 and 8years continuous cropping respectively. The pot and field experiments'results showed that the content of soil microorganism and the activities of soil enzymes have different trend at vary cropping years and different growing stages of tobacco.Now,we destribed them respectively.The field test reviewed that the activities of amylase increased first and then reduced along with the raising of tobocco cropping years.In the whole stage of tobacco cropping, soil enzymes showed a falling trend first and then increasing.As the raising of tobacco cropping years,the pot test reviewed that at 30d,75d and the field test showed tha at 30d,60d,75d and 90d they all showed a increasing trend first and then falling. In the whole stages of tobacco cropping, sucrase activities showed a falling trend first , then increasing and increasing at last.The activitiey of soil alkaline phosphtase with 4 years continuous tobacco cropping was larger than 0 years continuous tobacco cropping.The field test showed that the activitiey of soil alkaline phosphtase increased first and then reduced along with the raising in tobocco cropping years.In the different stages of tobacco cropping,enzyme activity reached highest at 30d(after transplanting),and falled lowest at its final stage(the pot test was at 90d,the field test was at 105d).As the raising of tobacco cropping years, the field test reviewed that at 45d,75d and105d the catalas activities followed a rule that they increased first and then falled. Except 30d, continuous tobacco cropping was larger than 0 years continuous tobacco cropping.Besides 6 years continuous tobacco cropping, the pot test showed a process that the catalas activities falled first , then increased and falled at last.As the raising of tobacco cropping years, the pot test reviewed that at 75d ,90d and the field test showed tha at 30d,60d,75d and 90d reductase activities showed a increasing trend first and then falling. At the different stages of tobacco cropping, compairing with the last stage ,the remaining stages were all higher than it (the pot test was at 90d,the field test was at 105d).The qualities of soil bacteria raised first and then falled as the raising of tobacco cropping years. The pot test showed that the qualities of soil bacteria were lower in 0 years continuous tobacco cropping and were higher in 8 years continuous tobacco cropping. The field test showed that the qualities of soil bacteria were lower in 0 years continuous tobacco cropping and in 8 years continuous tobacco cropping and were higher in 4 years continuous tobacco cropping and in 6 years continuous tobacco cropping. The qualities of soil bacteria showed a process as fallingt- increasing–falling, they reached their highest at 60d(after transplanting),and were lower at 30d (after transplanting)and 90d(after transplanting).The qualities of soil fungus showed a rule as raising-falling -raising as the raising of tobacco cropping years. They were lower in 0 years continuous tobacco cropping and in 6 years continuous tobacco cropping and were higher in 4 years continuous tobacco cropping and in 8years continuous tobacco cropping.The qualities of soil actinomycete raised fist and then falled as the raising of tobacco cropping years. They were all lower in 6 years continuous tobacco cropping than in 0 years continuous tobacco cropping .Except 45d,70d in pot and 75d in field, The qualities of soil ammonifier raised first and then falled as the raising of tobacco cropping years. The field test showd that the qualities of soil fungus followed a rule as raising-falling -raising as the raising of tobacco cropping years. In the field test, 4 years continuous tobacco cropping and 6 years continuous tobacco cropping were falled at first and then raised.As the raising of tobacco cropping years,pot test reviewed that at the whole stage of tobacco cropping, the qualities of nitrobacteria raised as the raising of the tobacco cropping years dependent the average value . The field test showed that at 30d,60d and 75d the qualities of nitrobacteria showed a increasing trend first and then falling.The qualities of phosphate-dissolving bacteria showed a falling trend first and then increasing as the raising of the tobacco cropping years, 4 years continuous tobacco cropping was the highest. The qualities of phosphate-dissolving bacteria reviewed that they falled at frist and then raised at the whole stage, they falled lowest at 30d(after transplanting)and reached highest at its final stage(the pot test was at 90d,the field test was at 105d).The results of potandfieldtests all showed that the qualities of potassium-dissolving bacteria all showed a falling trend first and then increasing as the raising of the tobacco cropping years.Three methods were used to try to extract and identify the soil microbial from plowland of tobacco,the results showed that the method 2 and method 3 (GC/ MS)were satisfied. These three methods identified 34 kinds of organic compounds, fatty acids,phenols, long chain alkane,alcohols and esters were included, some of them were considered as allelochemicals,the remaining compounds were the potential allelochemicals,but the allelopathy of these compounds in tobacco are still to illustrate.