506 PRINCIPLES OF SOIL MICROBIOLOGY 



form of ammonia. The presence of an available carbohydrate does 

 not inhibit, but rather stimulates the multiplication of the bacteria; 

 it lessens, however, the amount of protein to be utilized, and, therefore, 

 the amount of ammonia accumulated. Doryland 3 explained this by 

 the fact that the organisms utilize the ammonia as a source of nitrogen 

 and the carbohydrates as a source of energy. Thus, in the presence of 

 available carbohydrates, two factors are at work: (1) less of the protein 

 is decomposed since the bacteria and fungi may prefer the carbohydrate 

 to the protein as a source of energy, (2) the ammonia that has been 

 formed from the decomposition of proteins may be reassimilated by 

 the microorganisms which utilize the carbohydrate as a source of 

 energy. These organisms are, therefore, competing with higher plants, 

 for the available nitrogen compounds in the soil. As a result of these 

 studies, Doryland defined ammonification as "an expression of an 

 unbalanced ratio for microorganisms, in which the nitrogen is in excess 

 of the energy-nitrogen ratio." If the available energy material is equal 

 to or is in excess of the energy-nitrogen ratio required by the flora, the 

 coefficient of ammonia formation tends to approach zero; it tends to 

 approach a maximum, if the available energy material is less than the 

 energy-nitrogen ratio. Depending on the proportion of energy material 

 to nitrogenous substances, "beneficial" bacteria may become "harmful." 

 This is brought out in table 45. 



Bac. subtilis produced, in the absence of glucose, 1 mgm. of 

 NH 3 for every 49 mgm. casein decomposed. In the presence of 

 glucose, 1874.1 mgm. of casein was decomposed; this should have 

 produced 38.2 mgm. NH 3 , whereas only 11.9 mgm. were found. The 

 difference between the actual amount of ammonia present in the glu- 

 cose medium and the amount that would have accumulated, had 

 the glucose been left out, is 26.3 mgm.; this quantity of ammonia 

 must have been assimilated by the bacteria. At the same time, 1934 

 mgm. of glucose has disappeared or about 13 mgm. of NH 3 for every 

 1 gram of glucose. The amount of nitrogen utilization by Bac. sub- 

 tilis, with casein as a source of nitrogen, was found to be considerably 

 greater than the nitrogen assimilated by this organism from inorganic 

 salts in synthetic media, with glucose as a source of energy. This is 

 due not only to the actually greater assimilation of nitrogen, but also 

 because the organisms had at their disposal the energy that was made 



3 Doryland, C. J. T. The influence of energy material upon the relation of 

 soil microorganisms to soluble plant food. N. D. Agr. Exp. Sta. Bui. 116. 1916. 



