Degree Type

Dissertation

Date of Award

1989

Degree Name

Doctor of Philosophy

Department

Agronomy

First Advisor

Richard M. Cruse

Abstract

Most theoretical soil water and heat transport solutions are valid only for uniform soil material with uniform transport properties. This restriction reduces the validity of these solutions to laboratory or artificially created soil conditions. Variable soil conditions created by wheel traffic, tillage, surface configurations, surface mulches, and shading must be considered if soil water and temperature conditions are to be adequately described under field conditions. A finite element solution to the governing equations for coupled water and heat transport was developed for this purpose. This solution can include nonuniform thermal and hydraulic properties and nonuniform boundary conditions in the problem specifications. Soil inputs for the model include parameters describing the soil water desorption curve, soil bulk density, particle size distribution, organic matter content, and the saturated hydraulic conductivity. Test results against analytical transient heat transport and water transport solutions show the numerical solution to be stable and convergent on a close approximation of the analytical solution;The solution was used to estimate ridge configuration and wheel traffic effects on soil water and temperature conditions. Input parameters for the model were based upon field-measured soil properties from the plant row, untracked interrow, and the tracked interrow of three tillage studies. The plant row generally had the least bulk density, the greatest saturated hydraulic conductivity, and the greatest volume of large pores compared with the interrow positions. The wheel-tracked position had the greatest bulk density, least saturated hydraulic conductivity, and smallest volume of large pores. Hydraulic characteristics, as demonstrated by water desorption curves, varied with position;Several examples of water and heat movement in soils with spatially variable properties are discussed. Water and heat flow in a ridge are different than with a flat surface. Soil warming and drying seems to increase with ridge height on 80-cm row spacings. However, as ridge height increases beyond about 20 cm, ridge height changes have less effect on changes in soil warming and drying. Variable soil properties had little effect on predicted soil temperature distributions over a five-day simulation period, but had a greater effect on the predicted matric potential distributions.

DOI

https://doi.org/10.31274/rtd-180813-9086

Publisher

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

Copyright Owner

Joseph G. Benjamin

Language

en

Proquest ID

AAI9003502

File Format

application/pdf

File Size

198 pages

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