O INTRODUCTION 



the plant the right kind for the particular soil. Fer- 

 tility springs from these and from all other contributions 

 that secure a soil environment to the liking of the grow- 

 ing plant. Hence, the plant food of the soil is an incident, 

 but a necessary incident, just as heat and air and water 

 and tillage and texture are incidents and prerequisites of 

 high production. 



