| Chang'an District is located in the Guanzhong Plain, the south of vast Qinchuan, from east, south and west sides guard of Xi'an, is an important ecological barrier, is also building one of the Xi'an satellite modern metropolis. With the rapid economic development and accelerated urbanization, environmental quality suburban soil more and more attention. Suburban soil quality and use patterns for urban agriculture and development plays an important ecological role. Suburban diversity of soil use patterns, changes in soil quality determines the complexity. Physical and chemical properties of which change the accumulation of heavy metals in the soil directly influences the level of quality and sustainable land use and further development of urban agriculture and green food supply constraints. This article discusses the impact of soil properties and heavy metal elements, heavy metals pollution on soil testing and soil quality evaluation in the hope for the development of agricultural production of Xi'an City and metal pollution in soils and provide a reference.In this study, field investigation and data collection, choose Chang'an farmland, woodland, fruits and vegetables, the rice fields, nurseries five land use patterns, collection of 60 representative samples of surface soil mixture. Determination of samples of surface soil moisture, pH, conductivity, magnetic susceptibility, loss on ignition, such as physical and chemical properties of calcium carbonate, flame atomic absorption spectrometry determination of the soil samples Cd, Cr, Mn, Pb, Co, Cu,Ni, Zn and other heavy metals content of eight, the main conclusions are as follows:(1)Chang'an surface soil moisture during the sampling range of 3.4～25.2%, average 11.22%; pH value ranged between 6.42～8.57,60% of the test samples show alkaline; EC values range 0.05～0.96 ms/cm between the crop and plant growth in a safe range; low-frequency magnetic susceptibility ranges between 46.7～385.3×10-8m3/kg; high-frequency magnetic susceptibility range of 46.7～384.1×10-8m3/kg between; frequency magnetic susceptibility of the range between-1.8～11.11;changes in loss on ignition value range between 3.28～8.59%; calcium carbonate content in the range of 0～102.23 g/kg.(2) Result of the surface content of heavy metals in soil Cd was 0.98mg/kg (0.04～4.01mg/kg); Cr was 77.56mg/kg (2.35～107.15mg/kg); Co as 24.85mg/kg(15.15～31.89mg/kg); Pb was 44.89mg/kg(16.96～92.07mg/kg);Mn for the 500.19mg/kg (271.31～696.95mg/kg); Ni as 46.11mg/kg(13.37～62.42mg/kg);Cu was 33.03mg/kg (25.85～45.51mg/kg);Zn was 70.23mg/kg (47.86～215.79mg/kg).Average Mn elements in addition to, the other seven elements occurred at different levels of accumulation, which accumulated higher Cd and Pb elements. (3) Cd elements in arable land, fruit and vegetable, nursery type of surface soil, exceeding the percentage above the forest and rice fields; Cr element in the type of surface soil in the nursery exceeded the highest percentage in the other four kinds of modes are also more than 60%; Co element in all of the samples were excessive; Pb elements in the nursery and cultivated types of surface soil exceeded the percentage of high, forest and fruits and vegetables second, and rice fields not exceeding; Mn elements in arable land, rice fields and nursery types of surface soil,exceeding the higher the percentage, type of forest and fruits and vegetables to low; Zn element types in the forest soil under the surface, exceeding the highest percentage, fruits and vegetables to the smallest, followed by the other three types; Ni, Co, Cu three elements similar, the concentration in the test area more balanced, the calculated standard rate close to 100%, Ni elements in the cultivated land in the standard rate 97%, Cu element is only 1 less than the background value.(4) Statistical analysis showed that:moisture and pH, calcium content was significantly related; pH value and the frequency magnetic susceptibility, loss on ignition, was significantly correlated with calcium carbonate; low-frequency magnetic susceptibility and high-frequency magnetic susceptibility, frequency dependent susceptibility was significantly correlated;frequency magnetic susceptibility and calcium carbonate was significantly correlated; conductivity and pH values than the other physical and chemical properties outside the negative correlation, but correlation coefficients did not reach significant level; soil Cd and water, calcium carbonate was negatively correlated; Mn and pH, low-frequency magnetic susceptibility, high-frequency magnetic susceptibility, frequency dependent susceptibility, calcium carbonate significantly related; Cu and significantly related to loss on ignition; Zn and electrical conductivity, loss on ignition was significantly related; Pb and Cd was significantly correlated between elements, correlation between Co and Cr, significantly, Ni and Pb was significantly correlated between elements. Zn, Mn, Co, Cu was significantly correlated between the elements.(5)Single pollution index of Cr, Mn less than 1,indicating that not cause contamination, Cu, Zn in paddy soil showed moderate pollution, Pb in the paddy soil outside the above except 1,Cd in the five types of land pollution prominent; comprehensive pollution index of soil Cd were greater than 6, less than 12.Chang'an has emerged that heavy metal pollution in soil. View from the accumulation index, Cr mean value of 1.69, a medium degree of pollution, Pb, Co, Cu and Ni for the light-moderate pollution, Cr, Mn and Zn accumulation index is negative, indicating not reach pollution; surface soil Cd content of individual potential risk indicators are strong ecological harm, other elements of risk index less than 40, there is a slight ecological harm. Five integrated land use potential ecological risk index in between 150～300, the overall moderate potential ecological risk; under the soil environment quality standard (GB15618-1995) in the evaluation of heavy metals contained in the type area of five types of evaluation heavy metal content of land in line with second standard range. |
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