| Zhengzhou city lies in the transition between loess hill and Huang-Huai-Hai plain, so it has a variety of soil types. On the other hand, it locates in the region of transporting from the Eastern and marching to the market of the Western and rapid urbanization that brings about evident problems on soil quality and environment. In this paper, the districts that affiliated to Zhengzhou city, Jinshui, Zhongyuan, Guancheng, Erqi and Mangshan, were taken as the research area, 105 topsoil samples were collected from the above districts, several indicators, such as CEC, pH, organic matter contents and so on, were analyzed. Of the 105 samples, 56 were analyzed for total contents of 5 heavy metal (Pb, Hg, As, Cr and Cd). Based on the collected data of the second soil survey, with the help of GIS, the change of land use types caused by urbanization and which bring out the function transformation of soil resource, spatial-temporal change of soil fertility and condition of soil environment were studied. The main conclusions are as follows:(1) Function transformation of soil resource. In the course of urbanization, the soil resource function was mainly converted to the bearing function, among them, the area from the productivity function is 1377.93 hm2 and the ecological environment function is 142.56 hm2, most of them were converted to industry land. The soil area from the bearing function to the productivity function is 55.82 hm2 and to the ecological environment function is 0.53 hm2. Because the bearing function actually is productivity function of city soil, the city supports the development of city which depends on its bearing function. As a result, the transition change of soil function accord with the law of city development. The inner transition of productivity function was mainly from the field to orchard and pond, reaching 602.25 hm2. It reflected influence of urbanization on the surrounding agricultural planting structure, cropping was converted to more economically profitable forms of agricultural land use. The soil area from the productivity function to the ecological environment function is 101.57 hm2, while the contrary is 122.97 hm2, and mainly converted to the field.(2) The spatial-temporal variation of fertility. As for temporal variation, there was a general increase of the average contents of organic matter, total N, alkali N and available K, and by 7.31g/kg, 0.39g/kg, 11.15mg/kg, 38.36mg/kg and 1.55 mg/kg respectively in the suburb of Zhengzhou from 1982 to 2003. The improvement of soil nutrients is relative to the large amount of chemical fertilizers application every year, the straw return to soil, and "K supplement program" that Soil and Fertilizer Work Station of Henan Province carried out. As for spatial variation, the distribution of nutrient content was inclined to be homogeneous, especially for available P and K. Nutrient contents declined in the regions where they had been higher in the second soil survey, while nutrient contents increased where they had been lower. It was due to the fact that the application of fertilizer in the region where nutrient content was lower could get an more evident enhancement of production than where nutrient content was higher, which led to the difference of the application fertilizer. In the region of vegetable planting, rotation between rice and wheat, organic matter and total N contents were still high, showing the impacts of agricultural planting structure adjustment caused by urbanization on soil nutrient contents.(3) Heavy metal contents. for the five heavy metal elements, the main contents were all lower than their backgrounds, except for the content of Pb was slightly higher. The region whose contents of heavy metal elements were high lied in the dirty irrigation area of north and east, the west and where had been planting vegetable for a long time. From this we can see that irrigation using dirty water discharged by cities and factories was a key reason for the increase of soil heavy metal contents. On the other hand... |
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