384 MICROBIOLOGY OF SOIL 



be observed that more than 56 per cent of the nitrogen in the con- 

 centrated tankage was transformed into ammonia, whereas under the 

 same conditions cotton-seed meal yielded less than 5 per cent. 



Mechanism of Ammonia Production.- -The relatively large protein 

 molecules are readily broken into larger or smaller fragments. This 

 may be accomplished by purely chemical means, as, for instance, by 

 boiling with acids or alkalies, or by biological activities. Among the 

 first cleavage products albumoses and peptones are quite prominent. 

 These in turn undergo further cleavage and the various amino-acids 

 and their derivatives, as well as ammonia, make their appearance. In 

 so far as the different species of bacteria are concerned, the "hydrolysis of 

 proteins seems to depend, to a marked extent, on the ability to secrete 

 proteolytic enzymes. With the aid of such enzymes the proteins are 

 more readily hydrolyzed and further changed into amino- and hydroxy- 

 acids, ammonia and carbon dioxide. 



Influence of Soil and Climatic Conditions. Ammonia production in 

 the soil is affected by (a) its mechanical and chemical composition; by 

 (b) the amount and distribution of rainfall; by (c) the prevailing tem- 

 peratures; by (d) fertilizer treatment; and by (e) methods of tillage and 

 cropping. The mechanical composition of the soil influences the pro- 

 portion of aerobic and anaerobic species, while the chemical composi- 

 tion, particularly that of the humus, influences the rate of multiplica- 

 tion and the character of the chemical transformation accomplished. 

 It is well known, for example, that additions of fresh organic matter 

 intensify the rate of decomposition of the soil humus, and, likewise, 

 ammonia production as has been already demonstrated by Breal. In a 

 more general way it was proved by Lipman and his associates that, 

 with a constant bacterial factor, ammonia production in soils varies with 

 the chemical and mechanical composition of the latter. In some of 

 these experiments 100 g. portions of different soils were each mixed with 

 5 g. of dried blood, sterilized in the autoclave, cooled and inoculated 

 with equal quantities of infusion from fresh soil. The following 

 amounts of ammonia nitrogen were produced in six days: 



Soil Ammonia nitrogen found 



A 31.62 mg. 



B 68 . 29 mg. 



C 1 1 7 . 06 mg. 



D 107.16 mg. 



E 156.47 



