| With the development of commercial production of pepper,soil-borne diseases in pepper fields become more and more serious due to continuous pepper planting.The diseases caused by Phytophthora capsici are of worldwide economic significance and are very difficult to control.The trend is increasing year by year which affect the quality and yield of pepper.Farmers who are engaged in planting pepper suffered severe economic losses.At present,one of the best treatment for the management of soil-born diseases is pre-plant soil fumigation.Among them,dazomet as a potential chemicals not only can effectively kill soil pathogens but also low toxicity and application convenience.However,fumigants are a class of pesticide with broad biocidal activity and affect many non-target soil organisms.But there is few report about its effects of dazomet on soil-born diseases and soil microorganism.In the paper,the efficacy of dazomet to control soil-born pathogens and weed were conducted in laboratory.Combined with laboratory experiments,the effect of dazomet was tested in greenhouse pot experiments as well as field trials so as to evaluate the control effects of soil-born diseases and safety to pepper by investigating different points of disease,disease index and yield surveys.At the same time five determining quotas which were the soil microorganism quantity,soil respiration intensity,soil enzyme activity and soil microbial functional diversity and genetic diversity were chosen to study the effect of dazomet on soil microorganism for assessing the risk in soil microbial process.The study laid the scientific basis for the application of dazomet in pepper fields.The results were as follows:Laboratory studies found that EC50 values of dazomet to Sclerotinia Sclerotiorum,Sclerotium rolfsii Sacc,Phytophthora capsici and Pythium aphanidermatum were 0.445 mg/L,2.487 mg/L,3.264 mg/L,5.404 mg/L respectively,and EC50 values of 1,3-dichloropropene to four pathogens above were 24.845 mg/L,56.080 mg/L,10.817 mg/L and 11.211 mg/L,which suggested the activities of dazomet to four target pathogens were much higher than 1,3-dichloropropene.Besides that,there were the same result for Amaranthus retroflexus,Portulaca oleracea,Digitaria sanguinal and Eleusine indica.The relative toxicity ratios were 26.86,21.05,15.99 and 16.06.The Pot trials in pepper showed that dazomet was effective on controlling P.capsici,P.aphanidermatum,S.sclerotiorum and promoting the growth of pepper to some extent.Meanwhile,1,3-D could also control soil-born diseases of pepper,but its effects were not good enough.Field trials results revealed that dazomet applied to the field at 300,450,600 and 750 kg/ha could suppress P.capsici.The dose was higher,the effect was better.The controling effect was up to 94.44% for dazomet at 750 kg/ha.There had no significant difference in controling effect of P.capsici between dazomet at 300 kg/ha and 1,3-dichloropropene at 200 kg/ha.Two kinds of medicament could promote the growth of plants to some extent.The dynamic recovery of dazomet on microbial number was detected by the plate-dilution method.The results showed that Fusarium spp.and Phytophthora spp.were inhibited after the soil was treated with dazomet.There was not any pathogens that was found after treated with dose of 515.2 mg/kg.Dazomet had similar effects on soil bacteria,actinomycetes and physiological flora(ammoniation bacteria,cellulose decomposing bacteria,nitrogen-fixing bacteria),which were inhibition-stimulation-recovery.While soil fungi was suppressed strongly,and the doses were positively associated with the degree of inhibition.The number had significant difference between the treatment group and the control until the end of the test(P<0.05).Effects of dazomet on soil respiration were also studied in the paper.The results suggested that after the soil was treated with dazomet,soil respiration was inhibited at the beginning.Soil respiration started to activate at the 7th days after treatment,and there was a strong negative correlation between the time of stimulation and the dose of the treatment.As the extension of incubation time the activation effect got weakened.The respiration treated with dazomet could get back the normal levels completely at the 77 th days.Accorded to hazard division standard coefficient method,dazomet had little harm to soil.Effects of dazomet treatments on soil enzyme activities were detected in this study.The results reported that dazomet showed the strong inhibitory effects on the urease activity.The higher dose had greater effects on enzymatic activities,and the inhibition rate of the urease activity in the treatment of 515.2 mg/kg was still up to 88.74%;However,dazomet at all doses tested had inhibition-irritation-restoration effect on the activity of saccharase,catalase and phosphatase.On 77 th day,the activity of saccharase was close to that in the control treatment(P>0.05).To all of the doses of dazomet,soil urease activity presented inhibition impact.The effects of dazomet on soil saccharase,catalase and phosphatase were temporary without potential harm to soil fertility and crop growing.The effects of dazomet on soil microbial functional diversity was described through the carbon source utilization.The whole community of soil microbial activity at all doses were significantly lower than that of the control(P<0.05),and the dose showed the positive correlations with soil microbial activity.With the extending of incubation time,the microbial activity was gradually close to that in control.Low and middle doses has been restored to control levels at the 14 th day(P>0.05);Richness index,Evenness index,Simpson index under the test conditions had certain inhibition effects,but were back to control level at the 77 th day.31 kinds of carbon source material was divided into four categories: sugars and its derivatives,amino aoid and its derivatives,lipid and fatty acid kind,metabolic and secondary metabolites,according to test results suggested that sugars and its derivatives were the main use of carbon source microbial species.Result of effect of dazomet on soil microbial genetic diversity showed that: as the results of DGGE technology,dazomet can significantly reduce soil microbial abundance;With extended time,the difference decreased and similarities increased gradually.The maximum similarity was 81.5%.Bacterial richness,evenness and Simpson index gradually returned to control levels.The results by T-RFLP technique showed that bacteria number of the dazomet treatment at 0 d seemed to be a downward trend compared with the control.Compared with 0 d part flora had a tendency to restore at 7th day.The growth trend of 207 bp flora was obvious at 14 th day.The relative content of 147 bp flora reached maximum at 28 th day.The flora distribution was relatively uniform at 49 th day.The relative content of 152 bp and 159 bp were always higher than that in the control which belonged to Bacteroides,Bacillus,Paenibacillus and Streptomyces.The species contained some flora which had Strong resistance and distribut widely.This helped the degradation of organic matter and mineralization and had active effect on soil microbial breeding. |
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