The Effects Of Calcium Cyanamide Solar Disinfection On Physicochemical Properties And Microbial Community Of Facility Cucumber Soil

China has become a world of facilities agriculture.With the increase of planting years,soil continuous cropping obstacles significantly affect the healthy growth of crops.Soil microbial community and physicochemical properties are important factors of soil health indicators.As a safe,efficient and environment-friendly soil fumigant,calcium cyanamide（CaCN₂）can effectively prevent and control soil borne diseases of protected vegetables,solve the problem of soil continuous cropping obstacles,and ensure the safe production of vegetables.The previous studies on CaCN₂mainly focused on the soil-borne diseases control,while there were few studies on the effects of disease prevention on soil microecology,physicochemical properties and host crops.In this study,CaCN₂solar disinfection was carried out in protected cucumber production areas,vegetable straw returning areas and cucumber production areas of different soil types.In this study,the interaction among cucumber,soil microbial community and physicochemical properties in the CaCN₂treatment was studied in greenhouse cucumber production area,vegetable straw returning area and cucumber production area of different soil types by q PCR,amplification sequencing and macrogenome method.The main results were as follows:1.It is clear that the solar disinfection with calcium cyanamide has multiple effects on controlling cucumber root rot,improving soil fertility and increasing yield.The control effect of CaCN₂on cucumber root rot was 50.95%in protected cucumber production areas;Compared with non-disinfected soil,the p H value of CaCN₂ disinfected by sunlight increased by 0.52 units,and the EC decreased by 22.44%,which alleviated the problems of soil acidification and salinization;Meanwhile,the contents of soil OM,TN,AP and AK increased by 29.63%,70.37%,54.77%and 19.88%respectively,improving the physicochemical properties of the soil.The yield recovery rate of greenhouse cucumber was64.29%,which promoted the healthy growth of cucumber.2.It was determined that the number of soil microorganisms could recover to the initial level after 60 d in the CaCN₂treatment.The dynamic change of soil microbial community was detected in real time by dilution plate method combined with amplification sequencing technology.The soil microbial diversity decreased during CaCN₂ solar disinfection,and returned to the initial state 60 d after disinfection and membrane stripping.Compared with natural（non-disinfected）soil,the abundance of soil borne pathogens Fusarium and Olpidium decreased by 98.09%and 75.95%respectively after solar disinfection with CaCN₂,while the relative abundance of potential beneficial bacteria Pseudomonas,Bacillus,Lysobacter and Sphingomonas increased by 35.05%,30.33%,178.87%and 130.64%respectively,and showed positive correlation with soil p H and OM,forming a good soil micro ecological environment.3.The solar disinfection technology of CaCN₂is applicable to neutral and acid soil,not to alkaline soil.By measuring the number of culturable microorganisms,soil physicochemical properties and cucumber yield in facilities,the number of soil microorganisms recovered to the initial level after 60 d of solar disinfection with CaCN₂ in laterite soil,loam soil and chernozem soil.The Soil OM,AP and AK increased by1.75%～18.98%,13.70%～84.29%and 3.88%～21.28,respectively.The cucumber yield increased by 6.67%～46.67%in the CaCN₂treatment.However,the number of soil microorganisms failed to recover to the initial level after 60 d of solar disinfection with CaCN₂in saline alkali soil.The soil p H was 9.12（slightly alkaline）,the content of AP and AK decreased by 60.00%and 44.17%respectively.Therefore,to determine the suitable soil type for solar disinfection with CaCN₂can continue to use and promote green soil disinfection technology.4.It was revealed that the solar disinfection with CaCN₂enhanced soil enzyme activity and carbon metabolism.The macro genome sequencing technology was used to analyze the soil carbon and nitrogen metabolism pathway and enzyme activity.The abundance of glycoside hydrolase related genes in the soil was increased by 18.58%～32.55%in the CaCN₂treatment,and significantly positively correlated with the soil p H,OM and beneficial microbial population（Pseudomonas,Actinobacteria,Firmicutes,Bacillus,etc.）.In addition,the abundance of soil cellulase gene increased by37.55%～68.24%,and the abundance of lignin enzyme gene increased by 20.22%～65.10%in the CaCN₂treatment.This effectively promoted the degradation of soil cellulose and lignin,and was conducive to the transformation of organic matter in soil.To sum up,this study revealed the interaction mechanism between soil physicochemical properties and microbial population structure in the CaCN₂treatment by control cucumber root-rot and its effect on soil microbial population.It provides theoretical basis for overcoming soil obstacles and sustainable utilization of CaCN₂ solar disinfection.