The Nitrifying Agencies 167 



or retard such losses. We know next to nothing of the 

 bacterial relationships under the changing conditions. 



Ammonifying power of soils. — Attempts are being 

 made now in soil-bacteriological laboratories to measure 

 the ammonifying power of different soils under varying 

 conditions of tillage and fertilization. Attention is 

 being given, likewise, to the separation of certain species 

 from their neighbors in different soils. To use the ex- 

 pression employed in the bacteriological laboratories, 

 pure cultures of the same species are made from different 

 soils, and compared as to their vigor in the production 

 of ammonia. That this work is of considerable impor- 

 tance is evident from the fact that ammonification is 

 an essential step in the transformation of soil-nitrogen. 

 Soils that have but a feeble ammonifying power will not 

 allow a healthy growth of crops, irrespective of the vigor 

 of any of the other important soil bacteria. Proper and 

 profitable plant development is dependent on the rapid 

 and economical transformation of the humus-nitrogen; 

 also, on the rapid and abundant supply of ammonia to 

 the bacteria that change it into nitrites and nitrates. 



Nitrification. — The processes involved in the change 

 of nitrogen compounds are at least three (page 161): 

 Ammonification, nitrification, and dentrification. Am- 

 monification we have just discussed. The other two 

 processes are so important that we shall consider each 

 of them in a special chapter (XVIII, XIX). 



