Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Agronomy

First Advisor

Robert Horton

Abstract

This dissertation consists of three studies of soil hydraulic properties. The hydraulic properties of soils are very important properties which deal with the transport of water and solutes in the soils. In the first study, Shelby tubes were used to collect undisturbed soil samples at depths of 2 to 12 m from several glacial till profiles. Saturated hydraulic conductivity and chloride breakthrough curves were made on the soil samples within the Shelby tubes as well as on soil removed from Shelby tubes and resealed into permeameters. Paraffin wax was used to seal soil into permeameters. Saturated hydraulic conductivity measurements indicated that conductivity decreased with depth from 1.85x 10[superscript]-6 cm s[superscript]-1 to 1.64x 10[superscript]-7 cm s[superscript]-1. Below a 9 m depth, however, the conductivity remained nearly unchanged. The results of saturated hydraulic conductivity and chloride breakthrough obtained from soil samples within Shelby tubes and soil samples removed from Shelby tubes were different. Larger saturated hydraulic conductivity values and early chloride breakthrough obtained from the soil samples within the Shelby tubes indicated side-wall flow effect;In the second study, undisturbed soil samples were obtained from the surface A horizon to characterize the effects of two tillage systems (no-till and chisel plow) and traffic on water retention and transport of water, chemicals and air in the soil. The results obtained in this study showed that in general tillage did not significantly affect these properties. Traffic generally affected these properties significantly. No-wheel traffic samples tended to retain more water at or near saturation than did wheel traffic samples. Wheel traffic reduced unsaturated and saturated hydraulic conductivity. Air permeability values were also decreased because of wheel traffic;In the third study, a method is presented for estimating unsaturated hydraulic conductivity from air permeability data. Twelve undisturbed soil samples were obtained from the surface A horizon of a Tama soil. Samples were collected from the middle of wheel traffic and no-wheel traffic interrows. Air permeability was measured for each sample at selected soil matric potentials. A theoretical model relating air permeability to air filled porosity was developed. The model contains a parameter that can be used to predict unsaturated hydraulic conductivity. The model parameter was determined for each soil sample by curve fitting the model to the measured air permeability data. The model parameter for each sample was then used to predict unsaturated hydraulic conductivity for each sample. Predicted unsaturated hydraulic conductivity values were compared to estimated values from transient outflow method. The results of this study indicated that unsaturated hydraulic conductivity can be estimated reasonably well from air permeability data.

DOI

https://doi.org/10.31274/rtd-180813-12025

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Mohamad Zaki Mousli

Language

en

Proquest ID

AAI9335004

File Format

application/pdf

File Size

131 pages

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