Study On Distribution Characteristics And Evaluation Of Heavy Metal Concentrations In The Growing Greenhouse Vegetable Soil Under Different Production Modes

In this study,we measured soil physicochemical properties,heavy metal concentration and available heavy metal concentration,and compared their dynamics,and evaluated their risk status based on a long-term experiment including three treatments(Conventional(CON),Low-input(LOW)and Organic(ORG)farming systems)which has been conducted in a vegetable-growing greenhouse located at the Quzhou Field Research Station in Hebei Province,China.The results of the research are as follows:(1)Different farming systems had no significant effect on soil p H value and TP concentration in 0~40 cm soil layer,but had significant effect on soil organic matter and TN concentration which showed as ORG>LOW>CON(P<0.05).0~40 cm soil layer p H value significantly decreased from 2012 to 2016,and soil organic matter,TN and TP concentration increased from 2012 to 2016 in 0~20 cm soil layer.We also found that soil depth significantly affected soil p H value,organic matter,TN and TP concentration,and soil p H value showed that 20~40 cm was significantly higher than 0~20 cm.But the contents of TN,TP and organic matter in 0~20 cm soil layer were significantly higher than those in 20~40 cm soil layer.(2)Different farming systems significantly affected the concentration of Cu,Zn,Cr,Cd,Pb,Ni and Co in 0~40 cm soil layer.In 0~20 cm soil layer,the concentration of Cd,Zn,Cr and Pb in the Organic farming system were higher than those in the Conventional and Low-input farming system,but the concentration of Cu and Co in Conventional pattern werehigher than those in the Organic and Low-input pattern.The concentration of Cu,Zn,Cr,Cd,Pb and Co significantly increased from 2012 to 2016 in 0~20 cm soil layer.We also found that soil depth significantly affected the concentration of Cu,Zn,Cr,Cd,Pb,As,Ni and Co.The concentration of Cu,Zn,Cr,Cd,Pb and Co in 0~20 cm soil layer were significantly higher than those in 20~40 cm soil layer,but the concentration of As and Ni in 0~20 cm soil layer were significantly lower than those in 20~40 cm soil layer.Based on the correlation analysis between soil properties and heavy metal contents,we found that soil p H was negatively correlated with Cu,Zn,Cr,Cd,Pb and Ni concentration.And soil organic matter,TN and TP concentration were positively correlated with Zn,Cd,Cr and Pb concentration.Based on the correlation analysis between Cu,Zn,Cr,Cd,Pb,As,Co and Ni concentration,it was concluded that Cu,Ni and Co may have the same pollution source,and Zn and Cr,Cd and Cu had the same pollution source respectively.But As had a special pollution source.(3)Different soil depths and production patterns had significant effects on available Cu,Zn,Ni,Cd,and Co concentration in greenhouse vegetable soils,which showed that available Cu,Zn,Ni,Cd,and Co concentration in 0~20 cm soil layer were higher than those in 20~40 cm and shown as ORG>LOW>CON.But available Cu concentration in 0~20 cm soil layer showed as CON>ORG>LOW.Different cultivation years in 0~40 cm soil layer had significant effects on soil available Cu,Zn,Cd,and Co concentration.In the Conventional farming system,the available Cu and Zn concentration in 0~20 cm soil layer increased firstly and then decreased.Available Cu and Zn concentrations in Organic and Low-input vegetableproducing increased from 2012 to 2016.In addition,available Cd concentration decreased from 2012 to 2016 in 0~20 cm soil layer,but in 20~40 cm it increased from 2012 to 2016.Based on the correlation analysis between soil properties and available heavy metal contents,it was concluded that soil organic matter,TN and TP concentraion were positively correlated with available heavy metals concentration.And there was a negative correlation between available Co concentration and TP concentration.Through the correlation analysis between the concentration of heavy metals and available heavy metals in the soil,it was concluded that Cu,Cd,Pb and Zn concentration were positively correlated with its available concentration.(4)Heavy metal accumulation index and pollution index were used to evaluate heavy metals in greenhouse vegetable soil.The evaluation results showed that in 0~20 cm soil layer the accumulation index of Cu,Zn and Cd was the highest.In addition,the accumulation index of Cd,Zn,Co,Cr and Pb under Organic vegetable producing was the highest,but the accumulation index of Cu under Conventional vegetable producing was highest.The accumulation index of heavy metals in the 20~40 cm soil layer was lower than those in 0~20cm.The results of risk assessment of heavy metal pollution in soil indicated that the concentration of Cu,Zn,Cd and Cr in the soil has exceeded the safe level of the Soil Environmental Quality Standards of China in 2016.And soil Cd,Zn and Cr under Organic farming system was the most serious.The comprehensive pollution assessment showed that soil in a vegetable-growing greenhouse under the Conventional,Low-input and Organicfarming systems located at the Quzhou Field Research Station in Hebei Province,China were subject to “mild pollution” of heavy metals in 2016,and the greenhouse pollution of the Organic vegetable producing was the most serious.The potential ecological risk single factors of greenhouse vegetable soils were averagely at the low level(except for Cd)following an order of Cd>As>Cu>Pb>Ni>Cr>Zn in 0~20 cm soil layer.In 2016,the ECd value in 0~20 cm soil layers reached a considerable level of Grade-III,and the ECd value in 20~40 cm soil layer reached a level of medium level II.The composite ecological pollution index(RI)was at a low-value level(Grade-I).