Compared to the soil in cereal cropland,the physical,chemical and biological properties of the soil in the protected field,such as organic matter,total N,available nutrient(N,P and K),exchangeable Ca and Mg,(acidity) and alkalinity,salinity accumulation and bio-activity,have obviously changed with the prolongation of cropping duration.This has decreased soil quality,impacted crop growth and potentially threatened human health.In order to sustain the vegetable production with high yield,high quality and high efficiency,it is of great theoretical and practical significance to study soil fertility and its affecting factors in the protected field cropping system.