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

 it conforms to acceptable stajidards of scholarly presentation and 

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

 degree of Doctor of Philosophy. 



Donald N. Maynard, Ghairma/i 

 Professor of Horticultural 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. 



William G. Blue 

 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. 



Gordon M. Prine 

 Professor of Agronomy 



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. 



Lawrence H. Halsey 

 Associate Professor of Horticulti 

 Science 



