Degree Type

Dissertation

Date of Award

1989

Degree Name

Doctor of Philosophy

Department

Agronomy

First Advisor

Robert Horton

Abstract

In soil containing macropores, both water and solutes can move preferentially, bypassing much of the soil matrix. This can lead to rapid and far-reaching transport of agricultural chemicals, but may also be beneficial if soil water bypasses solutes. Information is needed that describes the conditions under which water and solutes move preferentially. In addition, the importance of preferential flow as a contribution to the net transport of water and solutes needs to be defined;This study is composed of two parts, a field study and a laboratory study. The objectives of the field study were to examine the transport of chloride in a soil that is known to contain many large and continuous macropores, to characterize the spatial variability of measured solute transport properties, and to obtain a data set for modeling. A chloride solution was applied to field plots and followed by irrigations of chloride-free water. Soil samples were collected in a square grid pattern so as to yield depth-concentration profiles below each surface gridpoint. The convection-dispersion equation was fit to each concentration profile to yield estimates of D, the dispersion coefficient, and v[subscript] s, the average pore-water velocity. The parameters D and v[subscript] s were found to be lognormally distributed but showed no spatial correlation for separation distances of up to 3 m. The average pore-water velocity v[subscript] w, calculated by dividing the known flux at the soil surface by the average profile water content, was greater than v[subscript] s, indicating that soil water moved preferentially through large pore sequences and bypassed the chloride residing in relatively smaller pores within the soil matrix;The objective of the laboratory study was to examine the effect of solute application method on preferential solute transport in undisturbed soil materials containing differing degrees of macroporosity. Experiments were conducted in which a chloride solution was applied to the soil surface in two different ways and then leached through the soil with chloride-free water. The resulting breakthrough curves for the two solute application methods were distinctly different, indicating a sensitivity of the transport process to solute application method. In addition, the curves showed that the sensitivity to application method decreased with decreasing soil macroporosity.

DOI

https://doi.org/10.31274/rtd-180813-13049

Publisher

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

Copyright Owner

Gerard J. Kluitenberg

Language

en

Proquest ID

AAI9014915

File Format

application/pdf

File Size

134 pages

Share

COinS