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I v'1''' PRINCIPLES OF SOIL MICROBIOLOGY PRINCIPLES OF SOIL MICROBIOLOGY BY SELMAN WAKSMAN A. Associate Professor of Soil Microbiology, Rutgers University, andMicrobiologist ofthe NewJerseyAgricultural ExperimentStations LT) ru m_D r-=1 ru o m o LONDON BAILLIERE, TINDALL AND COX 8 HENRIETTA STREET, COVENT GARDEN, W. C. 2 1927 ALL RIGHTS RESERVED, 1927 PRINTED IN AMERICA COMPOSED AND PRINTED AT THE WAVERLY PRESS BALTIMORE, MD., U. 8. A. In the years oftheir seventy-fifth and seventieth anniversariesrespectively, this book is dedicated to Professors M. W. BEIJERINCK and WINOGRADSKY S. the investigators who have thrown thefirst UgJd uponsomeofthemost importantsoilproc- esses and whose contributions can well be consideredfirst andfore- most in the science ofSoil Microbiology PREFACE Although the biochemical processes in the soil as well as the nature of the microorganisms present there have received considerable atten- tionfromvariouspointsofviewand although anextensiveliteraturehas accumulated, not only dealing with soil processes in general but even with certain specific activities of the organisms, our present knowledge of the soil microflora and microfauna and of the numerous transforma- tions that they bring about has not advanced beyond a mere beginning ofa systematic study. The isolation ofnumerousmicroorganismsfrom the soil, their identification and cultivation upon artificial media is veryimportantbut such data do not tellwhat role they playin the soil. A knowledge of the activities of certain organisms isolated from the soil is certainly necessary, but that is not a knowledge of the extent to which these processes take place in the soil itself. A book on soil microbiologyshouldincludeastudyoftheoccurrenceofmicroorganisms in the soil, their activities and their role in soil processes. It is this last phase which has been studied least and where the information available is far from satisfactory in explaining what is taking place in the soil. This is due largely to the limitations of the subject which depends for its advance on botany, zoology, bacteriology, chemistry, including biological and physical, and especially upon the advance of our understanding of the physical and chemical conditions of the soil. There are various kinds of audiences to which a book on soil microbiology may appeal. There is the scientific farmer who may search for a better understanding of the processes taking place in the soil, those processes which control the growth of his crops and indirectly influence the growth of his animals. There is the agronomist, who is interested in the fundamental reactions controlling soil fertility, by reason ofthe need of directing such processes towards a greater utilization of the nutrients added to the soil or stored away in the soil organic matter. Thereis theinvestigator, thesoil chemistorthe soilmicrobiologist,who, in attacking problems dealing with the occurrence of microorganisms in the soil, their activities, and especially with the relation of these activities to the physical and chemical soil conditions, seeks for specific or general information. These investigators may deal with organisms Vlll PREFACE or processes which could be better understood when correlated with the other soil organisms and the numerous other processes. An attempt has beenmade to compile abookwhichwill beofservice not only to the investigators in soil science, but also to workers in allied sciences, especially botany, plant physiology, plant pathology and bacteriology, as well as to the general student in agriculture. This book is a collection of known facts concerning microorganisms foundin thesoilandtheiractivities;itis astudyoftheliteraturedealing with the science in question; it is an interpretation of the facts already presented; itindicatesthevarious lines ofinvestigation andnoteswhere further information is especially wanted. Soil microbiology is a science which is at the very base of our understanding of agricultural processes and the practice of agriculture; it comprises anumberofsciences. The book may, therefore, be looked upon more as an introduction to further research rather than as an ordinary text-book; as ofhelp to those work- ingin theallied sciences, who aredesirousofobtainingsome information concerning the soil population and its activities. Ifthisvolumewillhelp to disclose to thereadersomeof thenumerous interrelated processesin thesoil, ifitwill presentin aclearerlight to the chemist, the physiologist, the botanist, the bacteriologist and the zoologist the nature of the many scientific and practical problems awaiting the investigator, if it contributes in a small measure toward makingsoilscienceanexactscience, the authorwillfeel thathehasbeen amply rewarded. The author is greatly indebted to his various colleagues for reading and criticizing the different chapters of the book and for the many helpful suggestions generously offered, especially to Dr. H. J. Conn, of the New York Agricultural Experiment Station, for reading Chapters I and VI; to Dr. B. M. Bristol Roach, of the Rothamsted Experimental Station, and Dr. G. T. Moore, of the Missouri Botanical Garden, for reading the Chapter on Algae; to Dr. Ch. Thorn of the Bureau of Chemistry, for reading the Chapter on Fungi; to Dr. M. C. Rayner, of Bedford College, London, for reading the section dealing with Mycor- rhiza Fungi; to Dr. A. T. Henrici, of the University of Minnesota, for reading the Chapter on Actinomyces; to Dr. W. M. Gibbs, of the Idaho Agricultural Experiment Station, for reading the Chapter on Nitrifying Bacteria; to Dr. A. L. Whiting, of the University of Wis- consin and to Dr. L. T. Leonard of the Bureau of Plant Industry, for reading the Chapter on Nodule Bacteria; to Dr. R. Burri, of Liebefeld, Switzerland, and to Dr. I. C. Hall, of the Colorado Medical School,