416 NATURE AND PROPERTIES OF SOILS 



trates are generally designated as Nitrobacter. In practice 

 these bacteria are generally spoken of as nitrite and nitrate 

 Organisms. 1 The conditions favoring the two groups are 

 practically the same. As a consequence, nitrification is gen- 

 erally discussed as though the transformation was only one 

 step and depended on one group of organisms. 2 



Just as ammonification follows closely on putrefaction, so 

 nitrification closely accompanies the production of ammonia. 

 In fact, the processes are so well synchronized in a normal 

 soil that only traces of ammonia and nitrites are usually 

 found. The nitrates, however, may accumulate in large 

 amounts. 



Marked differences have been noted in the nitrifying 3 



1 While it was known from the middle of the nineteenth century that 

 nitrogenous compounds added to the soil quickly produced nitrates, it 

 was not until 1878 that Schloessing and Miintz demonstrated that the 

 process was biological. In 1890 Winogradsky succeeded in isolating 

 the organisms. As they do not develop on ordinary medium, as do 

 the decay and ammonifying bacteria, a special technique was necessary. 

 Winogradsky used silicic-acid-gel plates containing certain inorganic 

 salts, as he found that the presence of even small amounts of organic 

 matter prevented the development of the organisms. In the soil, how- 

 ever, well-decayed organic matter generally stimulates rather than de- 

 presses nitrification. For a review of literature and methods of isolat- 

 ing nitrifying organisms, see Gibbs, W. M., The Isolation and Study* of 

 Nitrifying Bacteria; Soil Sci., Vol. VIII, No. 6, pp. 427-471, 1919. 



a Kaserer has isolated an organism, which he called B. Nitrator, that 

 can oxidize ammonia directly to nitrate. He writes the reaction as 

 follows : 



NH 3 + H 2 CO, + O a = HN0 3 + H 2 + CH 2 a 



He thinks that the energy necessary for the completion of the reac- 

 tion is obtained from the formaldehyde (CH 2 0) as follows: 

 CH 2 + 2 = H 2 + C0 2 + Energy 



The correlation between carbon dioxide production and nitrate accumu- 

 lation lends probability to this theory. 



Kaserer, H., On Some New Nitrogen Bacteria with Autotrophic Habits 

 of Life; Noted in Exp. Sta. Eecord, Vol. 18, p. 534, 1905-1906. 



' The nitrifying efficiency of a soil is usually determined by treating 

 a 100-gram sample held in a tumbler with a suitable amount of ammonia 

 sulfate or some other readily nitrifiable material. After incubation for 

 a suitable period at optimum temperature and moisture, the increase of 

 nitrate nitrogen is determined. This method is merely comparative and 

 measures only the nitrate accumulation. Its value is limited as it does 

 not simulate field conditions. 



