Study On Spatial Distribution Characteristics And Environmental Influence Of Main Trace Elements In The Middle And Lower Reaches Of Heihe River’ Oasis Farmlands Soil

The soil from Shandan, Minle, Ganzhou, Linze, Gaotai of Zhangye city and Jinta’dingxin district of Jiuquan city in the middle and lower reaches of Heihe River’farmlands was studied in this paper. The physical and chemical properties of soil samples, the total and available contents of trace elements in soils were analyzed. The data collected were subjected to statistical and correlational analysis by using SPSS 17.0. By using geostatistics combined with GIS, the spatial distribution characteristics and environmental influence of soil trace elements in the study area were analyzed. The results prove that:(1)In the study area, the range of pH was 7.69-9.18, the soil were alkalescence and strong basicity; the range of organic matter was 2.42-52.77g/kg, the organic matter content was in moderate and higher levels; the range of content of carbonate was 33.11-258.68g/kg, the content was relatively high; the range of available phosphorus content was 0.47-34.67mg/kg, the content was below moderate level; the range of CEC was 1.60-24.80, the content was lower, so the capacity of preserving fetility of soils was weak.(2)The average contents of total Fe% Mn were below the background values of Gansu province in the study area, maybe potential lack of. The average contents of total Cu、Zn、Ni、Co were all higher than the background values of Gansu province, a certain degree of enrichment. The coefficient of variation of toal Cu, Zn, Fe, Mn, Ni, Co was 21.25%, 23%, 15.29%, 19.04%, 17.76%, 14.14%, respectively, except Co was weak variation, the rest were all moderate variation. Compare with the second soil census results throughout the country, the contents of available Cu and Zn were increased, the contents of available of Fe, Mn were decreased. The coefficient of variation of available Cu, Zn, Fe, Mn, Ni, Co was 51.35%, 84.52%, 64.82%, 73.39%, 45.95%, 74.03%, separately, belong to the strong variation. Based on the classification of soil available trace elements contents, the available Cu was rich and extremely rich, the available Zn was moderate and rich, the available Fe was moderate and rich, the available Mn was low and very low, the available Ni was moderate and rich. On the whole, the content of available Cu was rich in the study area, the contents of available Zn, Fe, Mn, Ni were lacked of different degree, the content of available Mn was especially insufficient.(3) The contents of total Cu, Zn, Fe showed the similar spatial distribution characteristics, ie., decreased from southeast to northwest as a whole, and with moderate spatial dependence, Which showed that the spatial distribution mainly caused by structural factors such as parent materials, soil-forming process and random factors as cultivation, fertilization and irrigation. The spatial distribution of total Mn decreased from southeast to northwest, and with strong spatial dependence. The spatial distribution of total Mn was mainly affected by structural factors, and affected by random factors was less. The spatial distribution of total Ni, Co presented patch shape characteristics, and with strong spatial dependence. The spatial distribution was mainly caused by human activities such as cultivation, fertilization and irrigation and so on, in addition to parent materials.(4)The spatial distribution of available Cu, Zn were zonal distribution characteristics, and with moderate spatial dependence. The higher value of Cu, Zn was in Ganzhou district, which maybe caused by human activities such as cultivation, fertilization, irrigation and parent materials and so on. The spatial distribution of available Fe, Ni was patch shape distribution characteristics, and with moderate spatial dependence. Which showed this was caused by human activities such as cultivation, fertilization, irrigation and structural factors such as soil type, climate and so on. The spatial distribution of available Mn, Co was zonal distribution characteristics, the trend was decreased from southeast to northwest, and with strong spatial dependence, which was mainly caused by parent materials, soil type and other structural factors.(5) Person correlation analysis showed that: the correlation between soil total trace elements was significantly positive. The contents of available trace elements and total trace elements were significantly positive correlation. The content of available trace elements were significantly negatively correlation with pH of soil, significantly positive correlation with the content of soil organic, CEC, content of available phosphorous.