254 



MICROBIOLOGY OF SOIL. 



proportions of nitrogen were transformed into ammonia in the course of 



six days: 



Dried blood 16. 74 per cent. 



Concentrated tankage 56.66 per cent. 



Ground fish 47 . 16 per cent. 



Cottonseed meal 4- 95 P er cent - 



Bone meal 16. 65 per cent. 



Cow manure, solid and liquid excreta 32.60 per cent. 



Cow manure, solid excreta ... 5-39 P er cent - 



The experiments were carried out in equal quantities of soil and with 

 equivalent quantities of nitrogen in the different substances. It will be 

 observed that more than 56 per cent of the nitrogen in the concentrated 

 tankage was transformed into ammonia, whereas under the same condi- 

 tions 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, ammonia production 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 and 

 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 temperatures; 

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

 The mechanical composition of the soil influences the proportion of 

 aerobic and anaerobic species, while the chemical composition, particularly 

 that of the humus, influences the rate of multiplication and the character 

 of the chemical transformation accomplished. It is well known, for 

 example, that additions of fresh organic matter intensify the rate of de- 

 composition of the soil humus, and, likewise, ammonia production as 

 was already demonstrated by Breal. In a more general way it was proved 

 by Lipman and [his associates that, with a constant bacterial factor, 



