Degree Type

Dissertation

Date of Award

1980

Degree Name

Doctor of Philosophy

Department

Theses & dissertations (Interdisciplinary)

Major

Water Resources

Abstract

Two problems on optimization of fresh water management in porous media soil systems were investigated. The first problem dealt with the use of surface barriers on tile-drained land during leaching operations. The barriers were designed to prevent direct flow to underlying tile drains and make leaching more efficient. The 0.1 m diameter tile drains were imbedded in an impermeable layer 2 m below the ground surface and drain spacings of 4, 8 and 16 m were investigated. Calculations were made for surface barriers that covered 25, 50 and 75 percent of the land for each case of tile spacing. Comparisons were made with cases of simple ponding with no barriers. A modified Gram-Schmidt method was used to generate constants for the normalized head equation in polar coordinates that described the system. Flow nets of equipotentials and streamlines for the flow areas were constructed and leaching fronts were added to the flow nets. An optimization technique, involving sequenced operations with and without surface barriers in place, to leach the flow area to a depth of 1 m was presented. Calculated results showed that the barriers reduced ponding times by factors of 2.0 and greater and water usage by factors of 2.5 and greater, over simple ponding for the cases of 8 m and 16 m tile spacings. The barriers were of no advantage for the cases of 4 m tile spacings;The second problem dealt with optimizing a seedbed for planting maize (Zea mays, L.) on the sides of sloped ridges and was a field study which compared an optimized seedbed with other seedbeds for emergence rates, stands and yields of maize. In the optimized seedbed, high compaction of the soil next to the seeds was theorized to increase upward flows of capillary moisture. The seedbed was in a ridge where excess water would drain away from the seeds. The sloped-ridge seedbed was also optimized for temperature by sloping the planted surface toward the spring sun for maximum energy interception. Optimization for mechanical impedance and aeration was by leaving the soil over the seeds uncompacted. Four years of results of replicated field tests are presented. Faster emergence, higher stands and statistically significant yield increases up to 1685 kg/ha are reported for the optimized method and its variations over conventional flat planting and top-of-ridge planting methods;Capillary moisture flow rates and distributions in surface compacted soil columns were investigated in a laboratory study. High surface compaction of 0.9 and 1.0 gm/cc bulk density soil gave higher flow rates than uncompacted soils of the same initial bulk density by factors of 1.5 and 2.

DOI

https://doi.org/10.31274/rtd-180813-5396

Publisher

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

Copyright Owner

Stephen Bruce Affleck

Language

en

Proquest ID

AAI8019620

File Format

application/pdf

File Size

176 pages

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