| China's northwest arid area of land accounts for about 1/3 which has a wealth of land resources and adequate light and heat conditions.In recent years,with the rapid development of electric power irrigation equipment and water diversion technology,a large number of high-lift pumping irrigation areas have sprung up in the Loess Plateau in the northwest.The construction of these projects has brought great economic benefits,ecological benefits and social Efficiency,However,in the creation of a huge benefit at the same time,some negative ecological problems gradually emerged.Extremely fragile ecological environment and long-term extensive irrigation methods have caused severe salinization or secondary salinization of land,which seriously restricted the development of local agricultural production.Therefore,it is of great practical significance to carry out research on soil salinization in irrigation area.Select “Jingtaichuan Electrical Lifting Irrigation District in Gansu Province”(hereinafter called as “JingDian Irrigation District”(JID for short))as a research area which is a large pumping irrigation district,located in the arid desert,It's ecosystem is completely open and water-soil resources environment is relatively closed.the irrigation district was built in the early 1970 s,After more than 40 years of operation,the response of water-salt transport situation in the irrigation district has appeared gradually,which makes the area a typical area to be used to study the characteristics of soil salinization and law of water-salt transport in arid pumping irrigation district.In this paper,JID was taken as the study area,the salinization status in irrigation district was grasped through field investigation and survey.And the causes of salinization were analyzed.At the same time,the causes of soil salinization were also analyzed preliminary.The salinization characteristics in irrigation district were analyzed through laboratory test and statistical analysis method.The HYDRUS-3D was used to simulate and analyze the law of water-salt transport in irrigation district.The main research results of this study are as follows:(1)In the study area,each layer soil showed salinization,and high salinity occurs simultaneously on the surface and bottom layer of the soil,and the salt content of each layer has a strong variability.in the soil profile,the most important cation of the soluble salt ions is Na+,showing a medium to high intensity spatial variability.the most important anion of the soluble salt ions is SO42-,showing a high intensity spatial variability.the soil pH average of each layer was more than 8.3,showing a downward trend from top to bottom,but the overall change is not large,spatial variability is small.The average of exchange sodium percentage(ESP)each layer were less than 1.5,indicating that the soil in the study area was still in the non-alkalized soil state.(2)Through the correlation analysis of the ion content of each soil layer in irrigation district we can know that,The soil total salt(TS)showed a significant positive correlation with Na +?CI-?SO42-.The strongest correlation is Na +;While the soil pH did not reach a significant correlation with the salt ions,and only showed good correlation with HCO3?.through the principal component analysis of soil plough layer in irrigation district we can know that,the first principal component has a high correlation with Na+?CI??TS?SO42-,indicating that these four indicators are closely related to soil salinization.Therefore,Na+?CI??TS?SO42-can be used as the characteristic factors of soil salinization in the study area.(3)Based on the numerical analysis of the law of water-salt transport under different furrow irrigation,it can be seen that the trend of soil water content in each soil layer is basically the same.From the depth of different soil layers,the moisture content of shallow soil affected by irrigation is larger,the deep soil moisture content is less affected by the irrigation.From the analysis of different furrow irrigation model,the deep water content of conventional furrow irrigation is higher than that of alternate furrow irrigation and fixed furrow irrigation.For conventional furrow irrigation,the vertical downward movement is stronger than the other two irrigation methods,The lateral movement of soil moisture is inhibited,From the root of the water absorption efficiency and water use efficiency considerations,conventional furrow irrigation is not conducive to root absorption.(4)The soil salinity was affected by furrow irrigation ways and irrigation amount,and the higher the irrigation amount,the greater the trend of soil salinity decrease,especially the surface soil.The desalination rate of conventional furrow irrigation is higher than that of the other two kinds of furrow irrigation,that is,the effect of salt leaching of conventional furrow irrigation is better than that of alternate furrow irrigation and fixed furrow irrigation.From the same way of irrigation,the trend of salt reduction is proportional to the increase of irrigation quota.From the view for a long period of time,Soil salinity showed a general trend of increasing,Salts continue to accumulate to the surface soil,each soil layers show different degrees of salt accumulation,such as the salt accumulation rate of 0~20cm soil layer,conventional furrow irrigation is 22%,alternate furrow irrigation is 10%,fixed furrow irrigation is 26%.Comprehensive view,alternate furrow irrigation has the best control effect on salt accumulation.The research results can be used as an important basis for the optimal allocation of water resources,the improvement of saline land and the efficient use of land resources in high-lift pumping irrigation district.It is of great significance to maintain the ecological environment safety in northwest China. |
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