INOCULATION OF SOIL WITH MICROORGANISMS 233 



Although the soil is a good medium for practically all of the 

 desired soil organisms so far known, and although one can isolate 

 from the soil most of the known saprophytic microbes if one looks 

 for them long enough, only those microbes are found abundantly 

 in a particular soil in which the necessary nutrients are available 

 and where environmental conditions are suitable. Numerous 

 organisms continually compete with one another for these nutri- 

 ents. Those microbes become predominant which are best 

 adapted to the soil and the particular set of conditions and are 

 able to utilize the nutrients found in that particular soil. A new 

 microbe can become established only after a change in the condi- 

 tions of the soil, or in the presence of a specific host plant or a 

 selective nutrient. When the host plant is removed or the selective 

 nutrient is exhausted, the specific organisms may die out, unless 

 the microbe has become adapted to the soil in such a manner as to 

 find other available nutrients; the microbe may also be resistant 

 to unfavorable soil conditions and capable of persisting until the 

 specific conditions again become established. The creation of 

 conditions favorable for the development of specific organisms 

 results in the appearance of the desired organisms, without recourse 

 to inoculation. Conversely, the inoculation of an organism into 

 the soil which is unsuited to its development cannot be expected 

 to be of value. 



The introduction into the soil of various other organisms than 

 those mentioned above has been recommended from time to time. 

 Most of these, on careful investigation, proved to have their value 

 based upon insufficient evidence. It has been claimed that certain 

 cultures were composed of numerous organisms capable of bringing 

 about a more active decomposition of the organic matter of the soil 

 than the ordinary microbes. Other preparations were claimed to 

 contain microbes capable of inducing nitrogen fixation in non- 

 leguminous plants. Still others were claimed to favor plant 

 growth in general or the growth of some particular plants, in some 

 unexplained fashion. The interest of the layman is often aroused 

 by the important activities of the microbes. This interest coupled 

 with incomplete knowledge of the nature of soil microbes and their 

 relationships to soil processes unfortunately presents an oppor- 

 tunity for dishonest exploitation by the charlatan. 



In conclusion, it may be restated that, with very few excep- 

 tions, all soil inoculants, other than those for legume bacteria, have 



