CHAPTER XXXI 

 Soil Inoculation 



Beneficial and injurious microbiological processes in the soil. The 

 growth of higher cultivated plants is usually taken as a criterion in 

 determining whether a certain microorganism or a certain microbio- 

 logical process is beneficial or injurious. But a careful study of these 

 processes and the organisms concerned can hardly justify such a strict 

 division in all cases. Some, like the nitrogen-fixing, the nitrifying and 

 the sulfur oxidizing bacteria, the various organisms decomposing cellu- 

 loses and proteins, are no doubt beneficial to the growth of higher 

 plants. Plant pathogenic fungi, like the various Fusaria, Rhizoctonia, 

 Pythium, etc., may, no doubt, become injurious, when environmental 

 conditions are favorable. We may even call denitrifying and sulfur 

 reducing bacteria harmful, although their action is indirect and depends 

 entirely upon the soil conditions. 



However, as pointed out above, some organisms may carry on proc- 

 esses in the soil which are both injurious and beneficial to the growth of 

 higher plants; a certain process may be beneficial at one time and in- 

 jurious at another. The question becomes then merely relative. A 

 fungus, like Trichoderma or Asp. fumigatus, decomposes cellulose 

 rapidly and is no doubt beneficial, but it also synthesizes considerable 

 protoplasm and stores away large amounts of nitrogen and it becomes, 

 therefore, temporarily injurious to higher plants. When a protein 

 is decomposed by fungi, smaller amounts of ammonia are liberated 

 than when it is decomposed by bacteria. When the protein is added, 

 an acid soil favors the development of fungi, while a neutral or alkaline 

 soil favor the development of bacteria. 



Facts like these as well as the conditions which may favor the 

 development of the different groups of soil microorganisms and the 

 presence or absence in the soil of the particular organism in ques- 

 tion, must be known before we can make use of the principle of soil 

 inoculation. This consists not merely in the introduction of useful 

 organisms which may be lacking, but also in making soil conditions fa- 

 vorable for the biological processes useful to the growth of higher plants. 



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