SOIL INOCULATION 287 



successful, must be accompanied by the rendering of the physical 

 a nd chemical properties of the soil ideal for the growth of the specific 

 organisms to be added. A few organisms placed in a new environ- 

 ment already containing millions can never hope to gain the ascend- 

 ency over the organisms naturally occurring in the soil, for they have 

 been struggling for countless generations to adapt themselves to the 

 environment and only those which are fitted have survived. The 

 problem becomes even more complicated when we recall the findings 

 of Lipman that the bacterial flora of a soil is in many cases entirely 

 changed by climatic conditions. On this account, it would appear 

 that ever to make soil inoculation a success the chemical, physical, 

 and even the biological condition must be made suitable for the 

 growth of the specific organism added. Furthermore, strains of the 

 organism must be used which have been evolved under similar 

 climatic conditions. 



S'oil Gains in Nitrogen. It is well established that many forms of 

 microscopic organisms possess the power of fixing nitrogen either 

 when grown alone or in combination with other organisms of the 

 soil. Many of these have been obtained in pure culture and their 

 morphology and physiology carefully studied. The most favorable 

 conditions for their maximum nitrogen-fixation in pure cultures in 

 liquid solutions have been accurately determined. Some of the 

 conditions requisite for their activity in soils are known, but on this 

 phase of the subject there are many gaps in our knowledge and much 

 work must yet be done before we can state definitely the part which 

 they play in the economy of nature and before we can say which 

 are the very best^methods for increasing their usefulness. Never- 

 theless, it is interesting to consider the results obtained by a few 

 workers. 



Berthelot's early laboratory experiments led him to believe that 

 sands and clays may fix in a year from 75 to 100 pounds of nitrogen 

 to the acre. In two exceptional instances he noted that nitrogen 

 was fixed by sands at the rate of 525 pounds and 980 pounds an acre, 

 but soils which contained fairly large quantities of nitrogen never 

 made markedly rapid gains. 



Thiele, on the other hand, maintained that while there is no doubt 

 that Azotobacter possessed the power of fixing free nitrogen, under 

 laboratory conditions, yet it is not certain that conditions would be 

 such in soils for any gain of nitrogen due to the activity of these 

 organisms. We have already seen, however, that the Azotobacter 

 do not require as high a temperature for nitrogen-fixation in soil as 

 he thought necessary. It is also certain that in most arable soil the 

 temperature is sufficient during a large part of the year for a fairly 

 rapid nitrogen-fixation by bacteria. 



Krainsky thinks that even better results should be obtained in 

 soils than in pure culture, for there the nitrogen-fixers grow in sym- 

 biosis with autotrophic organisms which make organic compounds 



