NUTRITION OF SOIL MICROBES 



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nutrition. It is not always possible or even necessary to isolate 

 a soil organism in pure culture; valuable information concerning 

 soil processes may be obtained even with so-called crude cultures. 

 For physiological investigations, however, pure cultures of organ- 

 isms are very desirable and frequently necessary. 



Nutrition of Soil Microbes. — The microbes bring about in 

 the soil various transformations which result in the liberation of 

 plant food in forms available to cultivated and uncultivated 

 plants. They find the soil a favorable medium for their activi- 

 ties, and also obtain from the soil a sufficient supply of energy and 

 nutrients required for 

 growth and reproduction. 

 Most of the numerous 

 microbes which inhabit 

 the soil are useful, while 

 some are or may become 

 harmful from the stand- 

 point of the practical agri- 

 culturalist. Since the 

 activities of soil microbes 

 are so closely associated 

 with plant growth, an 

 economic management of 

 the soil requires a thorough 

 understanding of these ac- 

 tivities and their direction 

 into the proper channels, f''V 12^- Sy^J^iotic nitrogen-fixing bac- 

 . terium; different strains of Bacterium radi- 

 SO as to reduce the m- ^jg^fa obtained from: (1) garden bean, (2) 

 jurious effects to a mini- goats rue, (3) vetch, (4) alfalfa (after Shunk). 

 mum and increase the 



useful activities to a maximum. Frequently the development of 

 toxic or unfavorable conditions for plant growth may be com- 

 pletely avoided or quickly overcome if, in the treatment of the 

 soil, the activities of the soil microorganisms and not alone the 

 higher plants are taken into consideration. 



In nutrition, microorganisms have much the same require- 

 ments as higher forms of life, but their existence as single cells 

 is much simpler than that of their multicellular associates. All 

 microbes require for their growth and synthesis of cell substance, 

 supplies of energy and several nutritive elements, essential for 



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