THE RELEASE OF SOIL NITROGEN 



123 



one bacterium does this: bacteriologists tell us that a 

 dozen or more kinds have been detected at this bad 

 work. If some nitrogen compound, like sodium nitrate 

 (NaNO 3 ), is present in the soil, these denitrifying bac- 

 teria, as a first step, seize onto it and take oxygen there- 

 from, reducing the compound sodium nitrate (NaXO 3 ) 



SOME BACTERIA THAT CAUSE THE FERMENTATION OF URINE 

 (after Beijerinck) 



to a nitrite (XaXO 2 ). At this point in the reduction, 

 another group of bacteria attack the compound now 

 sodium nitrite (XaXO 2 ) and obtain the rest of the oxy- 

 gen, thereby setting the nitrogen free. The same is true 

 of ammonia: either these same reducing bacteria or 

 others similar in nature act upon ammonia salts in a way 

 that frees the nitrogen from its combination, consequently 

 causing its loss to the soil. 



The significance of this is striking: it means that the 

 most costly, as well as the most important, fertilizing 

 element has departed to the air, where it possesses no 

 value to either plant or animal. 



What the farmer may do. A very comforting fact, on 



