| The physical-chemical properties and enzyme activity of facilities cultivated soils of six different cultivated years in Yangling area were determined by field survey, sample collection and laboratory analysis to explore the possible effect of different cultivated years on the soil properties and the evaluation methodology from the points of comprehensive fertility, biology and heavy metal pollution. The result showed that:1. Available phosphorus, nitrogen and potassium, organic matter, available manganese, copper and zinc content in facilities cultivation soil increased during first 5 years and then leveled off from 5th to 10th years, and they decreased with the soil depth increase. Soil nitrate and EC content rised significantly with cultivation year increase. There was a significantly correlation between soil nitrate and EC content in different soil depth, and this indicated that nitrate accumulation formed a risk on nitrate leaching and secondary salinizations in soil. Soil pH declined significantly with the increase of cultivation years. The decrease of soil pH was resulted from the accumulation of nitrate nitrogen, available phosphorus and organic matter. Soil pH, organic matter, available phosphorus and available zinc were the sensitive indexes to characterize the variation of soil with cultivation years.2. Enzyme activity of facilities cultivated soil was higher than that of grain fields and nomal vegetable fields. Enzyme activity increased to a certain value before decreasing with the cultivated time increase. The peak of urease activity and catalase activity appeared in 3rd and 7th year respectively. Invertase and Polyphenol oxidase both showed a highest activity in 5th year. Correlation between alkaline phosphatase activity and cultivated years was significant. Activity of urease, alkaline phosphatase and invertase decreased with facilities cultivated soil depth increase, higher activity of catalase and polyphenol oxidased in deeper facilities cultivated soil was observed. The correlation analysis showed that there was a significant correlation between urease activity and available nitrogen content in different soil depth. Invertase and alkaline phosphatase activity significantly correlated with available phosphorus, available potassium and available zinc content. A significant correlation also existed between alkaline phosphatase activity and organic matter content. Catalase and polyphenol oxidase did not correlate with soil physical-chemical properties in any depth. The path analysis revealed that soil nutrients, organic matter, pH and available micro-elements had direct effects on alkaline phosphatase and invertase; they were the main factors influencing soil enzyme activity. Base on the result, alkaline phosphatase and invertases were considered to be relevant enzymology indicators to evaluate the soil fertility.3. Cu, Zn, Ni, Cd, Cr and Fe content in facilites cultivated soil increased with cultivated years, and the Cu, Ni, Cd, Cr and Fe contents were higher than grain field and normal vegetable land soils, while Zn content was lower. Mn remained unchange in all planting mode. During the different soil depths, Cu, Zn, Cd, and Cr content in surface soil is higher than the underlying soil, while Fe, Mn showed no significant differences. Ni content change in all the layers had no fixed rule. To evaluate facilities cultivated soil by single-factor pollution index method, result showed that: in every layers, include 0 ~ 10,10 ~ 20,20 ~ 40 cm of soil, heavy metal pollution levels were Cd> Ni> Zn> Cu = Cr, among them, the pollution index of Cu, Cr, Zn were smaller, the pollution was not serious, however, Cd pollution was more serious, followed by Ni pollution. The pollution index of Cd and Ni decreased with soil depth. Cd pollution is currently the most serious problems in agriculture. Nemero integrated pollution index showed that minority of the integrated pollution index in Yangling facilities cultivated soil were at the alert levels, most of the them were light, but have not yet reached the degree of medium or heavy pollution levels. The situation should be more concerned to take certain measures to control soil environmental quality. Using the Hakanson potential ecological risk index to assess facilities cultivated soil quality in Yangling, results showed that Cu, Zn, Ni, Cr potential ecological risk indicators in the different depth were at a range of mild ecological harm, while the Cd potential ecological risk index achieved in both the moderate or strong ecological risk. RI Multi-metal potential ecological risk index assessment showed that facilities cultivated soil in Yangling was at a low ecological risk overall.4. There was a significant correlation between heavy metals and enzymes in facilities cultivated soil: at different depths, Fe and catalase, Zn and urease had the most significant correlation; polyphenol oxidase and Zn, Cd were significantly positive or extremely significantly negative related in all layers; also there was a significant or very significant relation between intertase and Cu,Ni,Cd. Polyphenol oxidase and invertase can be used as the indicators of soil biological sensitivity on assessment of heavy metal accumulation. The reasonable interdependency between Cu,Cd,Zn and the physical and chemical property of facilities cultivated soil indicated that the planting and cultivation played a important role in the accumulation of Cu,Cd,Zn.Available phosphorus and potassium showed dramastic or extremely dramastic relativity with Fe, Cu, Ni and Cd, the result reflected that phosphate and potassium fertilizer had positive roles on the accumulation of Fe, Cu, Ni and Cd. The various relations between physical and chemical properties and heavy metals in 0 ~ 10 cm and 10 ~ 20 cm soil were more significant that the 20 ~ 40 cm soil.To assess the comprehensive soil quality by soil quality degradation index (SDI), the results showed that the degradation index of facilities cultivated soil was at the peak in the 7th year, meanwhile, the the situation was worse in the subsoil. With the increase of fertility, the enzyme were more active, however, the heavy metal pollution became more serious. The influence was more obvious in the surface soil as a result of that the crop had more effect on the surface soil.
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