132 TRANSFORMATION OF NITROGEN BY SOIL MICROBES 



tion, it has frequently been considered together with two other 

 processes, namely, nitrate fonnation and fixation of nitrogen, to 

 be synonymous with the microbiological activities in the soil. 



The amount of ammonia produced in the decomposition of 

 organic materials varies considerably, as illustrated in Table 30. 

 A series of different organic substances containing different 

 amounts of nitrogen were added to 100-gram portions of soil in 

 tumblers. The low amount of ammonia produced from rice flour, 

 corn-meal and wheat flour is due to the original low concentration 

 of nitrogen and comparatively high content of available energy 

 material. 



TABLE 30 



Ammonia Formation from Decomposition of Various Plant 

 Substances* (from Lipman) 



Substance used 



Nitrogen contained 



in the added organic 



matter, mgm. 



Ammonia formed 



in 7 days, 



mgm. 



Rice flour 



Corn -meal 



Wheat flour . . . . 

 Cowpea-meal . . . 

 Linseed-meal . . . 

 Soybean-meal . . . 

 Cottonseed-meal 



46.4 

 51.2 

 94.8 

 156.8 

 247.0 

 245.6 

 246.1 



1.30 



1.22 



5.05 



50.36 



118.31 



132.43 



123.63 



* 4 gm. of organic material added to 100 gm. of soil. 



The addition of organic matter free from nitrogen and repre- 

 senting an available source of energy will depress considerably the 

 amount of ammonia accumulating from the decomposition of the 

 organic substance, as seen in Table 31. A small amount of nitro- 

 gen-free organic matter actually produced an accelerating effect 

 upon ammonia formation, but larger amounts reduced the ammonia 

 formed from the decomposition of the nitrogenous substance; the 

 greater the amount of non-nitrogenous substance added, the less 

 ammonia was produced. This is due to the fact that a part of 

 the ammonia is used up by the organisms that utiHze the starch 

 and sucrose as nutrients; the presence of these also partly depresses 

 the decomposition of nitrogenous organic matter. The mechanism 

 of these changes is further discussed in Chapter IV. 



