| This research of soil water dynamics for changing bulk density consists of three parts. First, the dynamic relationship among water potential, water content and bulk density was obtained by inducing a variable of bulk density into soil hydraulic parameters; then, models of soil water characteristic surface and soil unsaturated hydraulic conductivity surface were developed; and finally, soil water flow equation for changing bulk density was built based on the results as mentioned above. In this dissertation soil water characteristic surfaces for five soils were measured under precisely controlled conditions. The feature of bulk density changes and the relationships between bulk density and soil water parameters were analyzed. Soil water characteristic surface model, unsaturated hydraulic conductivity surface model and one-dimension horizontal water flow equation were developed for the soils with changing bulk density based on the current theories and methods. The results of this study can be concluded as follows:1. During measurement of the soil water characteristic curves, water content and soil volume decreased, while soil bulk density increased with the increase of the suction. The turning point of bulk density appeared when the suction is 40.8m water. The bulk density changed greatly when the suction is lower than 40.8m water, and tended to be stable when it is over 40.8m water. The shrinking-swelling curves for four soils with different textures can be divided into structural portion and normal portion, and be described well by the Straight Line Model. Bulk density and shrinkage characteristics of the soils varied in great deal when soil texture changed from loam to clay soil.2. The power function relationship between bulk density and suction can be derived from combining Brooks-Corey model with soil linear shrinkage model. It was proved by measured data that the power function could describe the changing process of suction with bulk density well. The parameter, A ' , increased with the decrease of the sand content. A three-point method for taking bulk density change into account was used to determinevalues of bulk density change in the measurement. The method used bulk densities at saturation, the minimum, and maximum values of suction as control points.3. In general, assuming constant bulk density may cause the big error or even mistakes in soil hydraulic parameters, compared with the results taken changing bulk density into consideration. The accuracies predicted by the methods used in this dissertation with different bulk densities showed that the accuracy distributed symmetrically as the center of optimal bulk density. The closer was the distance between any bulk density and the optimal density, the higher was the accuracy. Compared with the soil water characteristic curves which took bulk density changes into account, two parameters obtained from those curves of assuming constant bulk density, a and 6 r, were slightly smaller and the parameter A was greater. Different bulk densities affected A slightly, and a was higher for smaller bulk density. With the change in texture from loam to clay soil, unsaturated hydraulic conductivity and soil water diffusivity decreased gradually. Saturated hydraulic conductivity, unsaturated hydraulic conductivity and soil water diffusivity all decreased when bulk density increased.4. Soil water characteristic surfaces in the soils studied in this research with changing bulk density were spatial surfaces consisted of water content, bulk density, and suction instead of a curve. If the values of suction were same, water content was higher for smaller bulk density and tended to decrease with the increase of bulk density. The difference of water content for different bulk densities was great when the soil texture became clay. The statistic results indicated that soil water characteristic surface may be expressed as a power function. It was found that there was close relationships between three coefficients, a, b, and c, and clay content.5. Saturated...
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