| The variation of soil water, salinity and temperature in the field makes the coupled transport processes of them very complicated. In recent years, such problems as the extension and application of on-film irrigation, reclamation of salinized soils, and prevention of secondary salinization have made it important to study coupled movement of soil water, salt and heat transfer under plastic mulch in arid and semi-arid areas. This dissertation was supported by National Natural Science Fundation and Huo Yingdong Education Fundation. The technical routes in this paper are to 1 )combine theoretical analyses with laboratory and field studies with emphasis on the field studies, 2) combine field and laboratory tests with emphasis on the laboratory tests studies, and 3) combine theoretical studies with applications with emphasis on theoretical studies. The whole study focused on the characteristics of coupled movement of soil water, salt and heat transfer under plastic mulch. The results are as follows:(1) Based on soil temperature data measured at different time in the field, soil temperature characteristics under plastic mulch were analyzed at four locations: the middle, the edge, in-between the plastic film and uncovered spot; the characteristics of soil temperature profile from 0 to 25cm depth and the correlation of soil temperatures in different soil layers were studied at different time with and without plastic mulch; on the basis of analyzing temporal and spatial variations of soil temperature in a corn field, the relations between soil temperature and air temperature were established, and a new method that only uses air temperature to predict soil temperature profile at different time is proposed. The predicted results showed good accuracy .(2) Testing equipment systems for the coupled movement of soil water, salt and heat transfer were developed, including horizontal, vertical and three-dimensional trickle ones. These systems used advanced non-destructive measurement methods for dynamic measuring of soil water, salt and heat, which provided important conditions for realizing dynamic measuring under certain conditions when temperature can be controlled.(3) Sensitivity analyses were conducted for parameters in unsaturated soil conductivitymodel which was derived from redistribution process. The results calculated from measured data indicate that the sensitivities of conductivity to parameter b and n are higher than the other parameters. Moreover, there are good fitted power function relationship between thermal conductivity and soil water content, soil water suction and salt concentration. Meanwhile, based on the measured data of soil water content and soil temperature distribution under temperature-controlled conditions, according to Philip's empirical equation, through difference method, the water diffusivity under temperature gradient was calculated, which can be expressed as a power function of temperature.(4) Systematic studies were conducted on infiltration, semi-finite soil redistribution and limited soil redistribution under isothermal condition, emphasized the variation and characteristic of soil water and salt profiles. At the same time, according to the related theories, theoretical relation of soil water profile was established under the condition of ponded infiltration and limited soil redistribution, the results were verified with measured data and proved to be reasonable. In addition, similar analyses on soil water and salt characteristics in insufficient trickle irrigation were conducted. All these laid foundation for studying and analyzing the same problems in temperature fields.(5) Based on 1-D horizontal tests for coupled movement of soil water, salt and heat transfer, theoretical analyses on the influence of temperature gradient on soil water and salt movement were conducted. The results indicate that soil water moves from the warm end to the cool end in both gaseous and aqueous phases under temperature gradient, which causes changes of...
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