Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering

First Advisor

Robert Horton

Second Advisor

James L. Baker


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.



Digital Repository @ Iowa State University,

Copyright Owner

James M. Hamlett



Proquest ID


File Format


File Size

269 pages