DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 385 



With all other factors constant, chemical and mechanical differences 

 in the soil used were responsible for striking variations in ammonia 

 production, as indicated by the figures given above. 



The influence of temperature and moisture conditions is fully as 

 important as that of the chemical and mechanical composition of the 

 soil. The following data secured by Lipman may be cited in this 

 connection as showing the effect of moisture: 



One-hundred-gram quantities of air-dried soil were each mixed with 

 3 g. of dried blood and varying amounts of water added. The ammonia 

 formed was distilled off and determined at the end of eight days. 

 The amounts of ammonia nitrogen found were as follows: 



Water added Ammonia nitrogen found 



c.c . 4.13 mg. 



1 c.c. 4.13 mg. 



3 c.c 5.40 mg. 



5 c.c 10.64 mg. 



7 c.c 26 . 37 mg. 



10 c.c 49-57 mg. 



12 c.c 70.71 mg. 



IS c.c 93.90 mg. 



It appears, therefore, that ammonia production in soils rises or falls 

 as the rainfall or irrigation is increased or decreased, or as the soil water 

 is more or less thoroughly conserved by proper methods of tillage. In 

 the same way, seasons of high temperature favor ammonification while 

 seasons of low temperatures discourage it. This point is well illustrated 

 by the observations of Marchal that at o to 5 only traces of ammonia 

 were formed in his culture solutions; that at 20 ammonia production 

 was quite marked, and that at 30 the maximum was reached. More- 

 over, apart from the seasonal variations in any one locality, there is a 

 wide range in ammonia production, as we pass from the torrid to the 

 temperate and from the latter to the frigid zones. 



Species and Numbers. Ammonia production is a function common 

 to most soil bacteria. In the earlier experiments of Marchal, seventeen 

 out of the thirty-one species tested were found capable of producing 

 ammonia. Prominent among these ammonifiers were B. mycoides, 

 B. (Proteus) vulgaris, B. mesentericus vulgatus, B. janthinus, and 

 B. subtilis. Of a considerable number of soil bacteria tested by 

 Chester all but one were observed to produce ammonia. In Gage's 

 experiments with sewage bacteria, seventeen out of twenty species 



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