842 PRINCIPLES OF SOIL MICROBIOLOGY 



the development of methods for the direct examination of microorgan- 

 isms in the soil by H. J. Conn and recently by Winogradsky. We 

 possess now also a better understanding of the organisms concerned in 

 the oxidation of sulfur in the soil (Lipman and associates), while the 

 role of microorganisms in the decomposition of cellulose and other 

 polysaccharides in the soil (Hutchinson and Clayton, Fred, etc.) has 

 been made clearer; a knowledge of the controlling influence of soil re- 

 action upon the distribution and activities of soil microorganisms has 

 influenced certain practices; the same is true of our increased knowl- 

 edge of legume cultivation and inoculation (Hiltner, Whiting, etc.), 

 of the use of green cover crops, fallowing and soil cultivation. 



Present outstanding problems in soil microbiology. The science of 

 soil microbiology is in its mere infancy. New contributions open up 

 broader and broader vistas, rich in reward both to the investigator 

 and to practical men. The soil is the basis of all agricultural practice. 

 The population of the soil makes the soil what it is and not a mass of 

 debris containing all the elements necessary for plant growth in an 

 unavailable form; sooner or later a study of this population will be 

 recognized to be of most importance in the future advance of agriculture. 



We possess at the present time considerable information on the 

 organisms inhabiting the soil and on the chemical processes of many 

 of these organisms, under controlled laboratory conditions; but little 

 is known of the processes carried on in the soil itself, by the numberless 

 representatives of the soil flora and fauna. The transformation of 

 organic matter, the availability of the mineral elements, the fixation and 

 transformation of nitrogen, the best means for the preservation of the 

 nitrogen already present in the soil or manure, these are a few of the 

 processes which depend largely upon the activities of microorganisms 

 and which control the growth of cultivated plants. Some of the 

 outstanding problems in the science may be suggested here: 



1. Microscopic and cultural methods in soil microbiology, especially 

 those which tend to indicate the organisms active in the soil under 

 field conditions and their, role in the transformations taking place in 

 the soil. 



2. The soil population, nature, extent and activities; the com- 

 plexity of the population with its various associative and antagonistic 

 influences. It is especially desirable to know what role the animal 

 population, such as protozoa and nematodes, play in soil processes 

 and how they influence bacterial activities, also the interrelation 

 between the fungi and the bacteria and the r61e of actinomyces in 

 the soil. 



