Effect Of Reductive Soil Disinfestation On Alleviating Continuous Cropping Obstacles Of Tomato And Response Mechanism Of Soil Microbial Community

Reductive soil disinfestation?RSD?is a biological soil sterilization method,which can effectively control soil-borne diseases in the soil and quickly repair degraded soil.RSD can replace the chemical soil fumigation method,which is conducive to the sustainable development of agriculture.At present,although scientists are still conducting research on the RSD,but the mechanism of RSD is still not clearly.After RSD treatment,the research on the impact of crop cultivation is also very limited.In this study,three substrates with different C/N ratios were evaluated?alfalfa[AL],C/N=14;maize straw[MS],C/N=33;and rice straw[RS],C/N=68?,and the experimental set up included 10 groups,as follows:CK,without crop straw;RSD treatments with AL,MS,and RS,with three levels of addition?0.5%[L],2%[M],and 5%[H]?,yielding ALL,ALM,ALH,MSL,MSM,MSH,RSL,RSM,and RSH groups.Through research,the optimal C/N ratio and optimum amount of organic materials in the RSD are clarified,and the microbial ecological mechanism of RSD to alleviate the continuous cropping obstacle is understood.It provides a scientific theoretical basis for the popularization and application of RSD.The main research results are as follows:?1?During RSD treatment,compare to CK group,all RSD treatments significantly increased pH value of soil.At the end of RSD treatment,the result of pH showed that the C/N ratio of substrate lower,the pH higher in soil,when the amount of substrate same.The result of DOC showed that RSD clearly increased DOC content,and the lower C/N and higher addition amount of substrate,the more obvious the effect.Moreover,the DOC content in the soil gradually decreases with the treatment of RSD.During RSD treatment,compared to CK group,all RSD treatments notably eliminate the accumulation of the NO₃^--N content in soil,when the lower addition amount and higher C/N of substrate,the rate of elimination of NO₃^--N in the soil is slower.However,the NH₄⁺-N content in soil shows the opposite trend to NO₃^--N.Especially ALH treatment,the NH₄⁺-N content in the soil is as high as 979mg kg-1 at the end of the RSD.?2?During RSD treatment,the bacterial and fungal community structure significantly changed.In bacteria,compare with CK group,the different RSD groups clearly increased the relative abundance of Firmicute in different degrees.And when the amount of substrate added was the same,the effect of alfalfa treatment was the most significant.At the bacterial genus level,0.5%of the amount of substrate added can promote the growth of Flavisolibacter,while 5%of the amount of substrate added is more conducive to the growth of organic acid producer,such as Clostridium,Coprococcus,Oxobacter etc.,and at the end of the treatment of RSD,the relative abundance of these organic acid producer has decreased.In the CK treatment,the relative abundance of these organic acid producer was less than 1%throughout the treatment period.In fungi,ALM,ALH and MSH groups significantly reduced fungal ITS copy number in soil compared with CK group,and RSD clearly reduced the relative abundance of Aspergillus and Fusarium.Interestingly,ALH and MSH can cause Pseudallescheia to rapidly multiply while reducing pathogens,and their relative abundance is as high as 63.7%and 87%,respectively.Moreover,PCoA results showed that the community structure of bacteria and fungi in ALH treatment was significantly different from that of other RSD.The biological diversity of bacteria and fungi in each treatment was reduced during RSD treatment.?3?After tomato planting,0.5%substrate addition treatment is more favorable for the growth of Bacillus and significantly increased the relative abundance of Streptomyces in Acidobacteria.Tomato cultivation notably increased in the number of fungal ITS copies in the soil compared to pre-planting.The relative abundance of Aspergillus and Fusarium in fungi is still the highest in CK,which is significantly higher than that in all RSD treatments.There is also a fungus?Arthrographis?that multiplies in the ALH treatment after tomato cultivation,and its relative abundance is as high as 62.7%in the ALH treatment.The biomass results of tomato plants indicated that MSL treatment was more conducive to tomato planting,and in the three substrate treatments,0.5%of the substrate addition treatment could promote the growth of tomato.In summary,the lower C/N ratio and higher substrate addition were better improved soil physical and chemical property and sterilization,However,in all aspects,although ALH treatment can effectively improve soil properties,the sterilization effect is remarkable.But,the high nitrogen content in ALH treatment may not only cause ammonia toxicity to tomato plants,but also provide a large number of breeding conditions for the genus Pseudallescheia and Arthrographis.Rice straw has a significant effect on sterilization,but it is less effective in improving soil physical and chemical properties than alfalfa and maize straw,and its treatment will cause a large loss of nitrogen.The maize straw not only has a significant effect on inhibiting pathogenic bacteria,but also can significantly promote the growth of the beneficial microorganism Streptomyces,which is beneficial to the growth of tomato plants.Therefore,in terms of comprehensive soil physical and chemical state,microbial sterilization effect and tomato plant growth,it is recommended that the optimal C/N ratio of organic materials be 34,and the addition amount is 0.5%when treated by RSD.