Study On Mechanism Of Water And Solute Transport In Soil With Macropores

This paper studies the mechanism of transport of water and solute in soil with macropores through indoor and field experiment and mathematical model. The main contents are as follows: Research background and significance, influence factors, experiments, models and the applicant of fractal theory about transport of water and solute in soil with macropores were detailedly reviewed. The undisturbed soil core which was taken from Nanjing suburb field was scanned by CT, and CT scanning image of every transverse section in soil core was obtained. The images were dealt with by geographical information system software ARC/INFO and Maplnfo. Distributions of macropores in transverse and vertical sections were obtained. The distribution of macropores size in transverse section was characterized as logritharm F distribution. The undisturbed soil core that was taken from Liaocheng field in Shangdong province was scanned by CT. It was indicated that distributions of macropores in transverse and that of vertical section of Liaocheng soil are different from those of Nanjing soil, because forming mechanism and existing condition of soils are different and forming reason of macropores is also different. The soil water retention curves of undisturbed soil and that of disturbed soil were obtained by centrifugal machine. It was indicated that the soil water retention curve of disturbed soil is different from that of undisturbed soil because disturbed soil destroys macropores structure and soil texture becomes uniform. The comparing and analyzing experiment about moisture content in undisturbed soil and disturbed soil was conducted. It was indicated that the change of moisture content with time in two soils shows different distribution features: The change of moisture content in disturbed soil is more regular than that in undisturbed soil. Moisture content of disturbed soil is greater than that of undisturbed soil expect surface layer, and with the increasing of soil depth, the different of moisture content between undisturbed soil and disturbed soil shows increasing trend. The comparing and analyzing experiment about solute concentration in undisturbed soil and disturbed soil was conducted. It was indicated that the velocity of water and solute transporting in disturbed soil is remarkably less than that in undisturbed soil, and the time of B appearing in deep position is earlier than that in shallow position in undisturbed soil and disturbed soil; Reversenitrify intensity in soil enhances with the increasing of anaerobic degree. Increasing of moisture content is beneficial to reverse nitrify intensity action. Because the transport down of water in disturbed soil is obstructed, infiltrating water accumulates and moisture content approaches saturation. The concentration of NO} in disturbed soil is considerably less than that in undisturbed soil.The basic equation describing transport of soil water in soil and the basic equation describing transport of solute in soil were set up. Dealing with parameter in equation and equations' boundary and initial condition were introduced. Equation numerical solution is solved by using finite difference. To counter transport of water and solute in soil with macropores, it was proposed to divide the simulating area of soil into macropore area and matrix area according to the distribution of macropores in soil. Each area was endowed its saturated hydraulic conductivity and its dispersivity. Macropores' net structure was set up. The whole simulating area was endowed one soil water retention curve. The basic equations were applied to find the solution.The saturated hydraulic conductivity of soil matrix area and that of macropore area were calculated according to soil texture and experiment data. It was known that the saturated hydraulic conductivity of macropore area is two-quantity level greater than that of matrix area.According to the distribution of soil macropores obtained by CT scanning > soil water retention curves obtained by centrifugal mach...