818 PRINCIPLES OF SOIL MICROBIOLOGY 



Introduction of certain useful microorganisms into the soil. Among 

 the useful microorganisms, which we may want to introduce into the 

 soil are: (1) organisms, which carry on important processes beneficial 

 to a specific plant or to plant growth as a whole ; (2) strains more vigorous 

 than those already found in the soil; (3) organisms which destroy or 

 injure the development of organisms directly injurious to higher plants. 

 It is not merely sufficient to introduce the beneficial organisms, but the 

 soil conditions should be made favorable for the development of these 

 organisms. 



So far as our present knowledge of the soil biological processes is 

 concerned, the microorganisms which may be lacking in the soil, or 

 whose activities in the soil are to be stimulated are as follows: (1) 

 symbiotic and non-symbiotic nitrogen fixing bacteria; (2) sulfur-oxidiz- 

 ing bacteria; (3) nitrifying bacteria, and (4) microorganisms capable of 

 vigorous decomposition of the soil organic matter. The favorable 

 influence of small quantities of manure added to the soil is ascribed by 

 some investigators to the inoculating power of various bacteria pres- 

 ent in the manure, these organisms presumably decomposing the soil 

 organic matter more vigorously than the native flora. However, this 

 favorable action is probably due not to the organisms, but rather to 

 the presence in the manure of certain inorganic substances, such as 

 available nitrogen and phosphates, which stimulate the growth of 

 higher plants or of certain soil organisms. Most of the bacteria 

 capable of decomposing starches and celluloses in the intestinal tract 

 of animals are specific inhabitants of the tract and are not found in 

 great abundance outside of the animal. 1 Among the organisms which 

 may directly destroy or otherwise eliminate the activities of soil or- 

 ganisms directly injurious to higher plants, the following may be 

 mentioned: (1) the predacious nematodes, like Mononchus, which 

 destroy the injurious nematodes, like Heterodera or Tylenchus; (2) 

 saprophytic fungi which may act as a check to the development of 

 pathogenic fungi. 



Among the soil conditions, which may have to be modified, so as to 

 stimulate the development of organisms whose activities in the soil are 

 favorable to the growth of higher plants, the following may be included: 

 (1) a proper carbon-nitrogen ratio of the soil; (2) a favorable soil reac- 

 tion and presence of sufficient bases; (3) presence of inorganic nutri- 



1 Henneberg, W. Untersuchungen fiber die Darmflora des Menschen mit 

 besonderer Beriicksichtigung der jodophilen Bakterien im Menschen- und Tier- 

 darm sowie im Kompostd linger. Centrbl. Bakt., II, 55: 242-281. 1922. 



