During recent decades of research by a large group of agricultural scientists working in the diagnostic field, many new methods have been devised to aid farmers in fertilizing their crops more effectively. A major objective of this book is to bring together in one volume a comprehensive discussion of both the underlying theory and the practical application of these various techniques. To attain that objective, the services of a group of distinguished Scientists were enlisted to prepare the various chapters. These scientists are outstanding in their respective spheres of work, both as to theory and as to practice. The results of their totally unselfish cooperation in this enterprise are manifest in the several chapters that comprise this book.