196 SYSTEMS OF PERMANENT AGRICULTURE 



which is one of the most suitable compounds of nitrogen for plant 

 food. 



This, then, is the general process of nitrification (including am- 

 monification and nitrification proper) , in which the ammonifying 

 and nitrifying bacteria transform or transfer the nitrogen from 

 insoluble organic compounds into soluble nitrate compounds in 

 which it may serve as available plant food. Each specific class of 

 bacteria performs a distinct function. Thus, the ammonifying bac- 

 teria serve only to convert organic nitrogen into ammonia nitrogen; 

 the nitrite bacteria (also called nitrous bacteria) serve only to 

 convert ammonia nitrogen from ammonia or ammonium salts 

 into nitrous acid (HNO 2 ) or nitrites; and the nitrate bacteria 

 (also called nitric bacteria) serve only to convert nitrous acid or 

 nitrites into nitric acid (HNO 3 ) or nitrates. 



While we may assume that the nitrogen passes through the forms 

 of nitrous and nitric acid, those acids are never present in detectable 

 quantities, the presence of a salifiable base being essential for the 

 progress of these biochemical reactions. The final product is al- 

 ways a nitrate, except under artificial conditions, when nitrites 

 may be obtained in quantity in the absence of the nitrate bacteria. 

 Under the natural conditions existing in normal soils, even nitrites 

 can scarcely be detected, because of the quickness with which they 

 are converted into nitrates. 



The nitrate that is formed may be calcium nitrate, magnesium 

 nitrate, potassium nitrate, sodium nitrate, or even ammonium 

 nitrate, depending upon which base is present in the most suitable 

 form. In the nitrification of ammonium carbonate, (NH 4 ) 2 CO 3 , 

 the reaction will stop when only one half completed if no other 

 base is present, the final product being ammonium nitrate, 

 NH 4 NO 3 . 



(NH 4 ) 2 CO 3 + 3 O = NH 4 NO 2 + CO 2 + 2 H 2 O. 

 NH 4 NO 2 + O = NH 4 NO 3 . 



To continue the process beyond this point would require the 

 formation of appreciable amounts of free nitric acid, of which the 

 bacteria seem incapable. In the production of lactic acid in 

 the souring of milk, the lactic bacteria are capable of continuing the 



