阿拉尔绿洲灌区棉田土壤水分扩散率的测定

Measurement of unsaturated soil water diffusivity in cotton field of Aral Oasis irrigated district

土壤水分扩散率是研究土壤水盐运动的重要参数之一。在室内用非稳定流水平土柱法对塔里木河流域阿拉尔绿洲灌区棉田土壤水分扩散率进行了测定。建立了Boltzmann变换参数、土壤水分扩散率与土壤含水率之间的定量关系。结果表明:土壤水分扩散率与土壤含水率呈单调递增关系。当土壤含水率趋近饱和含水率时,土壤水分扩散率趋近于无穷大。因此,用指数函数或幂函数不能很好地刻画土壤水分扩散系数与土壤的体积含水量之间的定量关系。本文建立的土壤水分扩散率与土壤含水率之间的函数关系较好地反映了土壤水分扩散系数与土壤的体积含水量之间的客观规律。

Soil water movement parameters are necessary for the solution of the basic soil water movement equation. The unsaturated soil water diffusivity is one of the important parameters of studying soil water and salt movement. It is difficult to determine the unsaturated soil water diffusivity in the field. This paper describes the basic principle and method of determining soil water diffusivity by means of wet front advancing in a horizontal soil column in laboratory. The water diffusion processes and unsaturated soil water diffusivities in cotton field of Aral Oasis Irrigated District in Tarim River Basin have been determined and calculated using this method. The relationships between Boltzmann transformation parameter A and unsaturated soil water diffusivity D and soil water content θ were established quantificationally, and these relationships make the process of calculating unsaturated soil water diffusivity very easy. It is found that： the unsaturated soil water diffusivity is monotone increasing function with soil water content. When soil water content tends to saturated soil water content, the unsaturated soil water diffusivity should tend to infinity, but when independent variable equal to a constant, exponential function or power function also tends to a constant. So, exponential function or power function could not describe the quantitative relationship between soil water diffusivity and soil water content. The new function of unsaturated soil water diffusivity and soil water content presented in this paper better reflect the object laws of unsaturated soil water diffusivity and soil water content.