Investigation Of Soil Obstacle Factors And Analysis Of Influencing Factors In Protected Vegetable Fields

Protected cultivation has developed rapidly in China since 1970 s,being an indispensable part of chinese agriculture currently.However,with the popularization of protected cultivation,soil obstacle is becoming increasingly prominent.Although there have been some previous studies investigating soil acidification,secondary salinization and soil-borne diseases,the reports about the severity and causes of these problems in diverse regions is still lacking.In this study,the types,proportions and contributing factors of soil obstacle problems in the protected vegetable cultivation systems of Suzhou were investigated through field inteview and the analyses of soil samples collected from 314 plots.The proportions of traditional plastic shield greenhouse and advanced glass greenhouse were 93.0% and 7.0%,respectively.Greenhouses with planting years less than 5 years accounted for 49.4%,and the average year was 6.2.The greenhouses were mainly planted with leaf vegetables,and those only planted with fruits vegetables accounted for 21.1%.The planting years of the greenhouses planted with fruits were significantly less than those with leafy vegetables.The most common fertilization regime was the combination of chemical and organic fertilizers.The proportion of the greenhouses with a decreasing trend in crop yield accounted for 38.7%.The planting years had a certain influence on the stability of crop yield,but it was not a decisive factor.There was no significant difference in bulk density between the soils of protected cultivation and open-field.Soil acidification occurred in 61.5% of the surveyed greenhouses,indicating a severe problem.There was a significant difference in p H between the soils in the greenhouse and open-field.The soil p H fluctuated with the planting years.Soil p H was significantly positively correlated with the application amount of organic fertilizer,but with a low correlation coefficient.The soil p H of greenhouses in rotation was significantly higher than that in continuous cropping.Secondary salinization was observed in 11.8% of the surveyed greenhouse soils.The soil electric conductivity fluctuated with the extension of planting years.There was an extremely significant positive correlation between soil electric conductivity and nitrate content,with a correlation coefficient of 0.653,indicating that nitrate accumulation was one of the main causes of soil secondary salinization.The soil electric conductivity of advanced glass greenhouses was significantly higher than that of traditional plastic greenhouses.The content of soil organic matter fluctuated with the planting years.There was a significant positive correlation between the content of soil organic matter and the amount of organic fertilizer applied.The soil organic matter content of the greenhouses in rotation was significantly higher than that in continuous cropping.The content of available nutrients in the greenhouse soils was significantly higher than that in the openfield.The contents of nitrate nitrogen,available phosphorus and available potassium in the greenhouse soils were 22.6 times,8.9 times and 1.9 times of those in the open-field,respectively.The average contents of lead,arsenic,mercury,cadmium and chromium in the greenhouse soils were 18.03 mg/kg,10.93 mg/kg,0.086 mg/kg,0.098 mg/kg and 77.47 mg/kg,respectively,indicating a low risk of heavy metal contamination.With the increase of the planting years,an increasing trend in the ratio of the number of soil fungi to bacteria was observed,indicating a change in soil microbial community from bacteria-dominant to fungi-dominant.The ratio of soil fungi to bacteria was significantly negatively correlated with soil p H,and was positively correlated with soil inorganic nutrient content and organic fertilizer application amount.The abundance of Fusarium oxysporum and F.solani in the greenhouse soils were significantly higher than those of the open-field,while the abundance of R alstonia solanacearum was significantly lower than that of the open-field.The incidence of soilborne diseases in the greenhouses was not serious,and there was no significant correlation with the planting years.However,the incidence rate in the greenhouses with planting years more than 5 was higher than those with planting years less than 5.The disease incidence of tomato bacterial wilt was negatively correlated with soil p H,while the disease incidence of cucumber fusarium wilt has no significant relationship with soil p H.To sum up,considering the local actual situation,the primary soil obstacles in the protected vegetable cultivation system of Suzhou district are soil acidification,excessive nutrient content and high risk of soil-borne diseases,which cause the reduction in crop yield and quality and seriously hinder the sustainable development of local agriculture.The conclusion of this study can be used as a reference for the future investigations about the soils in the protected cultivation systems of other areas.