Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Agricultural and Biosystems Engineering

First Advisor

Robert Horton

Second Advisor

James L. Baker

Abstract

A substantial portion of the nitrogen (N) fertilizer applied under intensive Midwestern cropping is lost through nitrate-nitrogen (NO[subscript]3-N) leaching with percolating water. A tillage and fertilizer-placement system designed to isolate the fertilizer from downward water flow and to minimize NO[subscript]3-N leaching is desirable, both environmentally and economically. A ridge-tillage configuration, with placement of the potential NO[subscript]3-N source in the elevated portion of the ridge, appears to be one possible best management practice. Therefore, NO[subscript]3-N leaching under ridge tillage during the early growing season and immediately following fertilizer application is investigated;Past numerical modeling of water and solute transport for both saturated and unsaturated soil is reviewed. The finite element formulation for two-dimensional water and solute transport is presented. The FEMWATER-FEMWASTE computer code is used for simulation modeling and a comparison is made of the water and solute transport in ridge- and flat-tillage systems;Data from a field experiment indicate that placement of N fertilizer in the center of a ridge reduces NO[subscript]3-N leaching as contrasted to a similar placement for flat tillage, even though total water movement through both systems is comparable. Vertical NO[subscript]3-N movement is predominant (in contrast to horizontal movement) and increases as the amount of simulated rainfall increases;Results from model verification indicate that the two-dimensional model has potential application in predicting water and solute movement in the unsaturated soil profile. However, further modeling activities are needed (with additional subroutines to handle runoff-ponding conditions) to insure the validity of the model for microscale applications such as those in this particular study. With further refinements, the model should be a more useful tool to describe water and chemical movement through soil for various fertilizer placements and surface configurations.

DOI

https://doi.org/10.31274/rtd-180813-11968

Publisher

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

Copyright Owner

James M. Hamlett

Language

en

Proquest ID

AAI8805077

File Format

application/pdf

File Size

269 pages

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