Study On Soil Water-Heat-Salt Transfer During Freezing-Thawing And Its Simulation By SHAW Model

Resources and environment are important for sustainable development of human society and economics. While soil and water are the basic resource for environment and agriculture.Soil freezing and thawing is a major cause of occurrence-developing in the soil salinization on arid and cold region. It plays a significant role to study on soil water-heat-salt coupling transfer under freezing and thawing conditions in agriculture. Study the transfer law of freezing and thawing soil water-heat-salt after autumn irrigation based on the agriculture in Inner Mongolia Hetao irrigation areas. Reveal the mechanism of control soil salinization and irrigation in autumn. Leaching by irrigation to reduce salt concentration in the crop root zone is a traditional technique in this area. Because of its complexity, the problem of moisture-heat-salt transfer in feezing-thawing soils under nature conditions is far from being solved though considerable works have been done. By theory analysis combined with experiment study, the purpose of this study is to reveal the mechanism of soil salinization and develop an irrigation scheme of water-saving and control salt content for autumn irrigation.Based on 12 years(1994~2006) fields experiment, by analyzing the yearly variation of air temperature, soil temperature, moisture and salt and its statistic eigenvalue, the law of freezing-thawing soil water-heat-salt transfer under filed condition is the farther analyzed.Analyze the effects on soil water and salt transport under different irrigation requirements and ground water level by autumn irrigation experiment.The SHAW(the Simultaneous Heat and Water) Model developed by Flerchinger and Saxton in NWRC ARS USDA is used to study the soil water-heat-salt transfer during freezing and thawing in Inner Mongolia Hetao irrigation areas. Compared with SWAP Model, it not only simulates water-heat-solute transport from atmosphere, vegetation to soil under non winter, but also deals with soil freezing and thawing. The system is represented by integrating detailed physics of a plant canopy, snow, resides, frozen soil and unfrozen soil into one simultaneous solution. This paper simulated the course of soil freezing-thawing, the law of moisture-heat transfer and the initial water content effects on water-heat in seasonal freezing-thawing period. The dynamic variation law related with water and heat transfer are obtained, including soil moisture content, temperature, the depth of freeze, soil evapotranspiration and water flux taken into account exchange between water and heat transfer in soil-atmosphere continuum. The advantage of theory analysis is shown compared with experimental study.Then based on soil moisture and salinity in Inner Mongolia Hetao irrigation district, the SHAW is used to simulate the dynamic variation of the soil evapotranspiration, water and salt content for the 3 salinized soils, the 11 irrigation requirements in autumn and the 3 irrigation time. The reasonable water-saving irrigation scheme in autumn is quantificationally developed for the first time which aimed at the different salinized (slight, moderate, serious) soils in theory.The study on the freezing-thawing soil water-heat-salt transfer in freezing and thawing period for salinity district are developed in the thesis. It contributed to some foundation in theory for the study on the water-saving irrigation in autumn, which is quite important for agriculture in the Hetao irrigation area. Moreover, it is significant role for the water-saving renovation and soil salinization control of irrigation area in North China.