Study On Soil Water-salt Movements In Luanjing Irrigation Area, Inner Mongolia

This thesis is based on the research of National natural science funds-the recharge of deep-buried phreatic water from irrigation by the Yellow River and environment benefit of irrigation by the Yellow River. Inner Mongolia is one of the driest areas in China. Luanjing Irrigation Area is adjacent to the Teng Ge-li Desert where evaporation is large and precipitation is small, so the area is seriously short of water and if we want to develop agriculture we must depend on irrigation.This paper selects typical soil sections to do soil water-salt equilibrium test and analyses soil water-salt dynamic feature and its influencing factors based on analyzing the hydrogeological properties of unsaturated zone. The soil moisture transport model is built with the VS2DT software of WHI Unsat2.2, and percolation amount under the existing irrigation conditions is calculated, irrigation amount of corn is optimized and the water saving method of corn is suggested. Salt balance equation is created and the soil desalting amount after irrigation and the irrigation leaching time when the soil salinity will be reduced to low level are calculated.Firstly, the thesis collects hydrogeological conditions in the study area, analyses construction and mass constitution of unsaturated zone, and then selects typical soil sections to do soil water equilibrium test and analyses soil moisture dynamic state after irrigation according to the observation data. The irrigation percolation amount is accounted based on water equilibrium. The consequence indicates that: first, the impound ability of the sand fusion is maximum, the sandy loam is secondly, the sand and gravel is minimum, and water was stored primarily in sandy loam in double-deck while mainly in the sandy loam and sand fusion in layered construction after irrigation. Second, the irrigation percolation amount is contacted with the irrigation amount, soil moisture content before irrigation, interirrigation and soil texture intimately. The larger the irrigation amount and the soil original moisture content are and the shorter the interirrigation is, the larger the irrigation percolation amount is. At the same irrigation amount, the thicker the sandy loam is, the smaller the superficial percolation amount is. Third, the deepness impacted by the irrigation is finite and the irrigation percolation amount is little after the first irrigation because the soil moisture is very low after the evaporation in winter without irrigation.Secondly, the paper analyses the hydrogeological conditions of irrigation areas and property of unsaturated zones systematically and generalizes the soil moisture transport conceptual model of the study area. Soil characteristic curve and saturation conductivity are determinated to definite soil parameter. The boundary and initial conditions are concluded based on meteorological conditions and observation data of soil moisture in the irrigation area. The soil moisture transport model has been built and proved to be practical. The irrigation percolation on the typical soil profiles is simulated by the model and then compared to the irrigation percolation amount concluded by the water equalization. The result indicates that the percolation rates obtained with the two methods is basically uniform and contrast within 6%. Irrigation amount of corn is optimized under the existing irrigation conditions, and the water saving method of corn is suggested.Thirdly, chemical components of rain, irrigation water and soil water collected in field are analyzed. Do soil leaching experiment, create salt balance equation and calculate the soil desalting amount after irrigation. By detailed analyzing soil salt dynamic state and its influencing factor, it can be concluded that there is a relation between the original salinity and lithologic characters of the unsaturated zone. The salinity of sand fusion is higher, the sandy loam and sand and gravel are lower. The irrigation desalination is contacted with the construction of the unsaturated zone, lithologic characters, thickness, irrigation system and amount. The desalting of the sandy loam is easier than the sand fusion. The larger the soil original salinity and irrigation amount are, the larger the irrigation desalination is. The change of soluble salt content is great in soil at the beginning of the irrigation with the rapid desalting and large desalting amount. The upper salinity reduces gradually and moves downward and the desalting amount gradual decreases as the irrigation progresses.Finally, the paper generalizes properties of water-salt dynamic state in the study area and gives some water saving suggestions in response to the local specific situation as follows: take reasonable irrigation water to improve availability of irrigation water, modify irrigation technique and decrease field water loss, increase land cover to reduce soil evaporation.