I certify that I have read this study and that in my opinion it 

 conforms to acceptable standards of scholarly presentation and is 

 fully adequate, in scope and quality, as a dissertation for the degree 

 of Doctor of Philosophy. 



R. D. Rhue 



Associate Professor of 

 Soil Science 



I certify that I have read this study and that in my opinion it 

 conforms to acceptable standards of scholarly presentation and is 

 fully adequate, in scope and quality, as a dissertation for the degree 

 of Doctor of Philosophy. 



n )/ f MiL. 



R. N. Gallaher 



Associate Professor of Agronomy 



This dissertation was submitted to the Graduate Faculty of the College 

 of Agriculture and to the Graduate Council, and was accepted as par- 

 tial fulfillment of the requirements for the degree of Doctor of 

 Philosophy. 



December, 1980 



Dean ^/College of Ag 



ricuLl/ure 



Dean, Graduate School 



