Effects of Water and Salt Transport in Different Level of Secondary Salinization of Soil under Greenhouse Irrigation
|School||Sichuan Agricultural University|
|Keywords||greenhouse soil soil water retention curve fractal theory secondary salinzation water and salt transport water heat coupling|
It was concern of soil solute transportation study that physical properties of disurbed soil can or not reflect the actual situation on undisturbed soil, which was key to the results of disurbed soil columns in lab can or not be applied. The fractal approach suggested by Tyler and Wheatcraft was used to analyse the relationship between the fractal dimension for the disturbed and undisturbed soil and soil water retention curve. After the research found that there was great difference that the degree of secondary salinzation of greenhouse soil in China, and it was a key way to settle the problem of the secondary salinization in greenhouse soil by determined the scientific and rational solution to the irrigation water. Water and salt distribution in different levels of secondary salinization of greenhouse soil under the same irrigation was investigated through soil columns in lab. The conclusions were as follows:(1)fractal dimensions were all closely related to soil bulk density, with the same soil texture, the higher soil bulk density and the higher fractal dimension. A significant linear relationship was always observed between the fractal dimension of the disturbed soil and fractal dimension of the undisturbed soil. It was quite obvious that the predicted soil water retention curves agreed well with the measured data. So estimating the undisturbed soil water retention curve of the greenhouse soil based on the fractal dimension of the disturbed soil was feasible.(2)It was showed downward migration characteristics that different levels of secondary salinization of soil water and salt after treated 13-15 days. Top enrichment of soil salt was appeared under the secondary salinzational levels of 2g/kg and 4g/kg after treated 15 days, groundwater and surface irrigation was not connecting. The migration of relationship between ions and total salts in greenhouse soils, In addition to HCO3-, the relationship between remaining seven major salt ion content and the total salt was highly significant linear function, in which cations and anions respectively, Ca2+ and NO3- correlation coefficient of the highest. The soil layers of 0-5cm and 40-50cm were prominent with a good coupling effect of air temperature, soil moisture content and soil salt content. According to the establishment of the coupled model, as well as environmental factors on the impact of salt accumulation, the concept "Salt Activity Surface" was thus brought forward.(3)Ca2+ and NO3- ions showed "double peak" feature on the distribution profile in the irrigation of 5-15 days. With the increased level of secondary salinization, Ca2+、Na+ and NO3-ions leached more slowly while the return of salt time later. Migration of groundwater on the K+ had no significant effect. the K+ ion showed a "single peak" feature on the distribution profile after irrigation. SO42- ions was difficult to be leached out of topsoil under all the degree of secondary salinzation. Cl-ions leached more quickly and the return of salt time earlier. Migration of HCO3-ions were less affected by soil water redistribution. Factors from the environment perspective, Ca2+ in the soil surface and bottom were prominent with a good coupling effect of air temperature, soil moisture content and soil salt content, and both of the Ca2+ transport has a synergistic effect. K+ transport in 0-20cm soil layer affected mainly by water, while the 30-50cm soil layer mainly influenced by temperature, the time from the irrigation point of view, in 5-15 days after irrigation affected by temperature, but after 20 days affected mainly by water, while the 30-50cm soil layer mainly influenced by temperature, the time from the irrigation point of view, in 5-15 days after irrigation affected by temperature, but 20 days after irrigation affected mainly by water. Whether from the soil or the time, NO3-and SO42-transport influenced mainly by water.