DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 387 



than in the soil where no carbohydrates have been added; in soils to 

 which, aside from the protein, large amounts of available carbohydrates 

 have been added, no ammonia or only traces of it will be found. 



Ammonia is produced by microorganisms chiefly in the deanniza- 

 tion of the amino acids; when the carbon part of the molecule is used to 

 supply the energy required and the nitrogen part is not consumed in the 

 process of metabolism, it is left as a waste product in the form of 

 ammonia. When there is in the soil, in addition to the proteins and 

 protein decomposition products, a sufficient amount of available carbo- 

 hydrates, the microorganisms will use the latter as a source of energy 

 and will attack the proteins only in so far as they need nitrogen for their 

 metabolism. In that case no ammonia will accumulate in the soil; 

 such as is produced will probably be assimilated by the microbes. 

 But, when there is an insufficient amount of available carbohydrates, 

 the microorganisms are compelled to use the proteins not only as sources 

 of nitrogen, but also as sources of energy. More carbon will then be 

 oxidized to supply the necessary energy than there will be nitrogen 

 consumed; the excess of nitrogen will be left in the medium as a waste 

 product in the form of ammonia. The presence of only small amounts 

 of available carbohydrates will check for a short period the accumula- 

 tion of ammonia, but will also result in more active microbial flora 

 The latter, after all the carbohydrate is used up, will attack the proteins 

 present and may produce larger quantities of ammonia than if no 

 carbohydrate had been added. 



Rate of Ammonia Production. Miyake, using the results obtained 

 by Lipman, and Waksman, in his work on the ammonia production 

 byAspergillusniger, have shown that the rate of ammonia accumulation, 

 whether by a pure culture or by a mixed culture, is an autocatalytic 

 reaction. The rate of ammonia accumulation is at first slow, then it 

 begins to fall off and finally comes to a standstill. 



Relative Efficiency of Different Species. In Marchal's experiments 

 already referred to, the species employed showed marked differences in 

 their ability to produce ammonia out of egg albumin. The following 

 proportions of the protein nitrogen were converted into ammonia in 

 twenty days: 



B. mycoides 46 per cent B. subtilis 23 per cent 



B. (Proteus) milgaris 36 per cent B.janthinus 23 per cent 



B. mesentericus vulgatus.. 29 per cent B. fluorescens putidus 22 per cent 



Sarcina lutea 27 per cent B. fluorescens liquefaciens . 16 per cent 



