Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Thomas E. Fenton


Many who engage in soil survey have long desired discovery of a remote sensing technique that differentiates individual soil series. As research in precision agriculture has begun, many other agricultural scientists have also begun evaluating remote sensing tools for soil mapping purposes. Soil electrical conductivity (EC), as measured by instruments including the Geonics RTM EM-38, has shown promise as a soil survey tool. Most of the work done along these fines to date has involved comparing soil EC patterns to Order 1 or 2 soil surveys. It is important that we understand how certain field conditions that might be encountered during the course of a typical soil survey affect soil EC readings. Therefore, the purpose of this dissertation was to identify field conditions that might affect soil EC readings obtained with the EM-38 and then conduct investigations to determine what, if any, affect those field conditions had. The relationships between soil moisture and soil EC were investigated in the field, and between soil moisture, temperature, carbonate content, and soil EC were investigated in the laboratory. The possible influence of diurnal temperature changes and changes in bulk density in the upper few cm of the soil on EC readings obtained with the EM-38 was studied, as was the possible influence of crop residue cover on soil EC readings. Results show that soil water content is often highly correlated to soil EC, and the influence of soil water content is at least two orders of magnitude greater than the influence of soil temperature or carbonate content in determining soil EC. Diurnal temperature fluctuations and crop residues covering the soil surface did not affect soil EC values, but changes in bulk density did. Therefore, it was concluded that knowledge of soil moisture conditions might allow a soil surveyor to anticipate the expected range of soil EC values for a given soil series on a given day. No compensation needs to be made for diurnal temperature changes in the soil or for crop residue cover. However, more work is needed on how bulk density affects soil EC readings obtained with the EM-38.



Digital Repository @ Iowa State University,

Copyright Owner

Eric Charles Brevik



Proquest ID


File Format


File Size

148 pages