Preface.

It has long been the custom to regard soil chemistry from one of two diametrically opposed points of view. Either, it has been considered extremely simple, or complex and hopelessly difficult. In either case the impression has generally prevailed that practical work in soil chemistry consists in treating the soil with some solvent or other and analyzing the resulting solution for “available” plant food elements; in other words, that the chemist’s role in soil studies is merely that of an analyst.

Soil chemistry is complex, but not by any means hopelessly so. Unfortunately, the complexity of most of the problems presented has deterred the student of pure chemistry from attacking them, and because they do not offer any material pecuniary rewards, they have not appealed strongly to the investigator in applied chemistry. Investigations in soil chemistry, for their own sake, or for the sole purpose of increasing the sum total of human knowledge concerning the phenomena taking place in the soil, have been comparatively rare. The subject has generally been regarded from the analytical point of view and as incidental to agronomic studies.

One purpose of this little book is to show the investigator in chemistry who is not limited by the condition that his work must bring some personal financial return, that the soil and its problems offer a field for his efforts quite worthy of ranking along-side the most interesting branches of pure chemistry, as well as being of the very highest importance to the development of the welfare of the human race. Another purpose is to point out the line of attack upon the problems of soil chemistry which at this time offers the largest opportunity for results. In how far the details of the story in the following pages are correct, time with its further investigations will tell. In a sense, the correctness of the details is of secondary importance. It is of the first importance, however, that there should be a general recognition that soil phenomena are essentially dynamic in character, and that the investigation of the properties of the soil solution and its relation to crop production is a procedure certain to yield results of positive value.

Again, it is a purpose of this book to make available for students of agriculture, a systematic outline of the work so far accomplished in this particular field. It is to the students of to-day from whom are to come the investigations of the near future that the book is particularly addressed. Some of the details presented in the following pages are matters on which opposed opinions are now held strongly by different authorities, and to the unbiased minds of the coming investigators must be left the decision as to how closely the truth has been approximated in what is written to-day. The field of effort covered by this book is one in which there is an increasing activity, and new facts and deductions will inevitably bring modifications to present opinions. To encourage this further acquisition of knowledge is the main purpose of the book.

The material brought together in this book has been presented to the faculties and students of several of our Agricultural Colleges, in the form of a short course of lectures. In large part, moreover, it has been published in Volume XIV of the Journal of Physical Chemistry. To make it accessible to and more easily read by one familiar with the progress of technical soil investigations, it has been recast in its present form.

It has been assumed that the reader will have a fair working knowledge of the concepts of modern chemistry. Nevertheless, an effort has been made to avoid technical terms so far as this can be done without undue sacrifice of lucidity of expression. Free references have been made to the bulletins of the Bureau of Soils, U. S. Department of Agriculture, because they are generally accessible to the American student, and because in them will be found detailed discussions and bibliographical material pertinent to the subjects outlined here. To his coworkers, the author is indebted for many criticisms and suggestions; and more especially in the making of the book is he indebted to Mr. S. C. Stuntz.

Washington, D. C. 1911.

Table of Contents.

PAGE

Preface iii

I. The Soil 1

II. Soil Management or Control 4

III. Soil Analysis and the Historical Methods

of Soil Investigation 8

IV. The Plant-Food Theory of Fertilizers 16

V. The Dynamic Nature of Soil Phenomena 18

VI. The Film Water 24

VII. The Mineral Constituents of the Soil Solution 31

VIII. Absorption by Soils 59

IX. The Relation of Plant Growth to Concentration 70

X. The Balance Between Supply and Removal

of Mineral Plant Nutrients 75

XI. The Organic Constituents of the Soil Solution 79

XII. Fertilizers 105

XIII. Alkali 110

Index 127

AN INTRODUCTION TO THE STUDY OF THE SOIL SOLUTION.