Study On Property Evolution And Quality Evaluation Of Continuously Cropped Soil Of Protected Cucumber

The deterioration of soil quality caused by continuous cropping has become a bottleneck restricting the sustainable development of protected vegetables in China.However,due to the lack of soil quality grading and evaluation methods for continuous cropping of protected vegetables,the prevention and control,restoration and improvement of soil with continuous cropping obstacles in production are blind.In this study,the continuous cropping soil of greenhouse cucumber in Huang-huai-hai area was taken as the object.Based on the analysis of its physical,chemical and biological characteristics,the main factors inducing the change of soil quality were screened out,and the soil quality evaluation system was established.The soil quality of continuous cropping was divided into four grades: healthy,mild obstacle,moderate obstacle and severe obstacle,and the interaction of key quality factors was further explored.It laid a foundation for further revealing the mechanism of continuous cropping obstacles in greenhouse cucumber soil and formulating differentiated prevention and control strategies.The main results are as follows:1.With the increase of continuous cropping years of cucumber,the contents of pH,alkali hydrolyzable nitrogen,available phosphorus and available potassium in root zone soil first increased and then decreased,and the bulk density,organic matter,total nitrogen and total phosphorus content gradually increased,while the total potassium content was relatively stable.The Catalase activity increased gradually,the urease activity increased at first and then decreased,the sucrase and phosphatase activity changed little at the early stage and decreased sharply at the late stage.The diversity of bacteria and fungi in rhizosphere soil increased at first and then decreased,reaching the highest value around 6years of continuous cropping.The relative abundance of pathogenic bacteria such as Rhizoctonia and Fusarium and the relative abundance of biocontrol bacteria such as Bacillus and Sphingomonas increased gradually.Pathogenic antagonistic bacteria such as Chaetomium,Mortierella,Aspergillus and Penicillium,and nutrient transformation related bacteria such as Streptomyces,Pseudomonas and Nitrospirillum increased first and then decreased.The abundance of endophytic Bacillus and Agrobacterium increased year by year,while that of Chaetomium increased first and then decreased.2.The physical,chemical and biological properties of cucumber continuous cropping soil were screened by principal component analysis,and seven factors highly related to the change of cucumber continuous cropping soil quality,SC,AN,AP,bacterial diversity,TK,fungal diversity and EC,were obtained.By fitting and analyzing the factors selected from the structural equation model,the effects of the factors on the quality of continuous cropping soil were as follows: AN > AP > bacterial diversity > fungal diversity > SC > TK.Using the above factors to calculate the soil quality index could better evaluate the soil quality of protected cucumber.The soil quality of continuous greenhouse cucumber planting was divided into four grades according to SQI: healthy(SQI ≥ 0.61),mild obstacle(0.55 <SQI < 0.61),moderate obstacle(0.46 < SQI < 0.55)and severe obstacle(SQI ≤ 0.46).3.There is a high correlation between the key quality factors of soil in continuous cucumber cropping in greenhouse.The change of bacterial community was closely related to the content of SC and AN,the change of fungal community was closely related to the content of SOM and TK,and the content of endophytic microorganisms was significantly related to the content of SOM and SC.The Bacillus and Sphingomonas in the differential bacteria were positively correlated with multiple differential metabolites,and Aspergillus in the differential fungi were negatively correlated with multiple differential metabolites.The analysis of the interaction relationship among various factors showed that continuous cropping of protected cucumber could affect a series of metabolic pathways such as ABC transporters,Aminoacyl-tRNA biosynthesis,Alanine,aspartate and glutamate metabolism,cell membrane lipid synthesis and metabolism by changing the absorption and transformation of carbon,nitrogen,potassium and other elements in soil,thus affecting the composition of soil and endophytic microbial community;However,rhizosphere microorganisms may adapt to the stress caused by continuous cropping of cucumber by participating in fatty acid metabolism pathways such as propionic acid synthesis.