Study On The Influencing Factors Of The Effect Of Dazomet Fumigation On The Soil Of Panax Notoginseng Planting

Dazomet（Dazomet,DZ）,as a substitute for highly toxic pesticide fumigants（such as methyl bromide and chloropicrin）,can kill pathogenic microorganisms,nematodes and pests in the soil,and can solve the continuous cropping obstacles of crops.Improve crop yield and quality.It is widely used in strawberry,watermelon,ginger,Codonopsis,apple and other high economic value crops.The amount of dazomet fumigation and soil environmental factors will affect the soil fumigation effect.Panax notoginseng（Burk）F.H.Chen is a plant that is prone to continuous cropping obstacles.However,the research on the application of dazomet in P.notoginseng is rarely reported,and it is necessary to carry out systematic research.This study explored the optimal dosage of dazomet in the soil fumigation of P.notoginseng,clarified the changes of microorganisms in the soil,and explored the degradation rate of dazomet in different P.notoginseng planting soils through indoor experiments.Finally,the effects of different color film mulching on the fumigation of dazomet were studied.The main conclusions are as follows:（1）Different concentrations of dazomet（35 kg/666.7 m2,40 kg/666.7 m2,45kg/666.7 m2）fumigation could significantly reduce the abundance of Fusarium in soil and increase the abundance of Proteobacteria.After 18 months of dazomet fumigation treatment,it was found that the abundance of beneficial bacteria Gemmatimonadota and Chloroflexi increased,and the abundance of pathogenic bacteria Fusarium continued to decrease,and the effect of dazomet dosage of 40 kg/666.7 m2 was the best.At the same time,dazomet fumigation changed the structure of soil nutrients,promoted the accumulation of nitrogen,phosphorus and potassium,and provided nutrients for the growth of P.notoginseng.Among them,compared with the control group,when the concentration of dazomet was 40 kg/666.7 m2,the growth and development of P.notoginseng was the best,the content of nitrogen,phosphorus and potassium in each part was the highest,and the dry weight per mu of the main root of P.notoginseng increased by 9.74 times,and the saponin content increased by25.25%.（2）The degradation rate of dazomet in different soil types（yellow soil,red soil,black soil）was yellow soil>red soil>black soil,and yellow soil was 4.76 and 3.1-fold faster than black soil and red soil,respectively.Correlation analysis between dazomet residues and soil physical and chemical properties showed that dazomet（DZ）content was negatively correlated with soil bulk density（BD）（P<0.001）and soil potential of hydrogen（p H）（p<0.05）,and positively correlated with soil organic matter（OM）content（p<0.01）.The degradation rate of dazomet was accelerated with the increase of soil temperature and water content.When the soil temperature increased from 5℃to 25℃and the water content increased from 15%to 35%,the degradation rate increased by 79.31%～310.34%and 57.57%～287.88%,respectively.In addition,black soil,low temperature and high water content are more conducive to soil microbial recovery.（3）Under field conditions,the growth and development（stem height,stem thickness,stem weight,main root length,main root width,main root weight,shear weight and fibrous root weight）of P.notoginseng under black mulch treatment showed the best performance after covering different colors of mulch（white,black and blue）after dazomet fumigation treatment.All four saponins（Rg₁,Re,Rb₁and Rd）exhibited the highest levels under the black mulch treatment,except for saponin R₁which was the highest in the white mulch treatment.The tensile strength,elongation at break and crystallinity of different treatments were analyzed,the results showed that the fumigation of dazomet aggravated the aging degree of the film,which was white>blue>black.Analysis of soil microorganisms under different colors of mulch showed that the highest numbers of soil bacteria,fungi and actinomycetes were found under black mulch.The relative abundance of the beneficial soil microorganisms Escherichia-Shigella and Penicillium had the highest magnitude in the black mulch after dazomet fumigation treatment.In summary,the use of appropriate dazomet during fumigation can reduce the damage to the microbial community structure while ensuring effective control of pathogenic bacteria,increase the abundance of beneficial bacteria,and promote the growth and development of P.notoginseng.At the same time,different color mulches affect the fumigation effect of dazomet by changing the microenvironment of soil.Black mulch can prolong the persistence of dazomet in soil and increase the abundance of beneficial bacteria in soil.