Water And Salt Movement In Soil Of Takelamakan Desert Irrigated With Saline Water

The water flow and salt transport in Takelamakan Desert artificial oasis, which was irrigated with saline underground water, were been studied in this dissertation. To achieve the objective, a field plot experiment and the investigation on soil water and salt content were conducted in part of Takelamakan Desert artificial oasis where was under the condition of furrow irrigation, while another field plot experiment to focus on water and salt movement in soil under the condition of plot irrigation was conducted in other part of the artificial oasis. Later, some other experiments about simulating water flow and salt transport in soil under drip irrigation with saline water were conducted in field and laboratory. Using techniques such as statistics, water and salt conservation, and modeling on water and salt movement to the corresponding data measured from experiments, results were obtained as follows:1. The salt in soil of Takelamakan Desert artificial oasis mainly came from irrigation saline water. Before irrigation, the mainly soluble salt contented in primary soil is NaCl, but after irrigation one year, it would be Na2So4.2. The more amount of irrigation saline water, the higher soil water content, the lower soil salt content, and the deeper of zone of salt accumulated in soil. The effect of irrigation intervals on water and salt content in soil is reverse as that of irrigation water ammount. Treatments such as cover film, fertilized by chemical fertilizer and manure can enhance soil water content and reduce salt content in soil.3. Under furrow irrigation, the variation of salt content in soil within a year can be divided into 5 different stages, which are spring stage with strong soil water evaporation and salt accumulated in topsoil (from March to middle April), begin summer stage with salt losing in topsoil (from later of April to begin of June), Summer stage with no obviously change in soil salt content (from begin of June to middle of August), later summer stage with salt losing in topsoil (from later of August to later of September), winter stage with no obviously change in soil salt content (October to middle of March of next year). The salt content in soil declined gradually after furrow irrigation year by year.4. As for plot irrigation land, after stopping irrigation 24 hours, 8.85% of the amount of irrigation water would be contained in the soil layer of 0-150cm. After stopping irrigation 72 h, 3.4% of the amount of irrigation water would be contained in layer of 0-150cm, and average soil water content in this soil layer was 5.3%. After this time, soil water content in this layer reduced slowly. During the time from stopping irrigation to seventh day after stopping irrigation in autumn, the daily evaporation water amount was 2-6mm. 2 hours after stopping irrigation, soil water contained in the layer of 0-20cm moved upward to the surface of ground, while72-144 hours after stopping irrigation, the upward region of soil water extended to the depth of 90cm underground. When irrigated by saline water with EC value of 6.3ms cm"1, The EC value of soil solution reduced obviously in upper part of the layer and that in lower part of the layer was almost same as that of before irrigation. 24 h after stopping irrigation, the amount of salt contained in solution of layer of 0-150cm was less than that of before irrigation, while 144 h after stopping irrigation, it was only 53.46% of that of before irrigation. After stopping irrigation, the daily amount of salt accumulated on ground surface with area of 100X 100cm2 would be 13-35g in autumn.5. Under present drip irrigation condition whose discharge rate of water is 3.5L/h per drip hole, the contour of wetted front is like as a half ellipsoid during irrigation period. Under drip hole was an area with the highest value of water content, and a series of water content contours surrounded this area. The water contents of these contours reduced gradually from the area under drip hole to outer. At the beginning stage of stopping irrigation...