I3O AGRICULTURAL BACTERIOLOGY. 



CHAPTER VI. 

 RECLAIMING LOST NITROGEN. 



THE LOSS OF NITROGEN. 



IN spite of all that can be done to prevent it, there is a loss 

 of nitrogen from the soil. While some of the nitrogen ex- 

 tracted from the earth by the plants has gone through a series 

 of transformations and has been brought back again into the 

 condition of plant food to be incorporated into the soil, a con- 

 siderable portion of it has had quite a different history. This 

 loss of nitrogen to the soil is brought about by several means, 

 the chief of which may be briefly summarized as follows : 



1. A considerable portion of the nitrogen is carried off to 

 the ocean. The bodies of animals and plants that, after death, 

 chance to fall into streams are carried to the rivers and to the 

 sea. Much nitrogen is taken from the soil and carried to the 

 city as human food. Most of this may eventually find its way 

 into the sewage system which empties into the streams and, 

 unless previously dissipated, ultimately reaches the ocean. 

 When the nitrogen has reached the ocean it is, of course, 

 beyond the reach of the plants growing on the soil, even if no 

 further change occurs. 



2. Denitrification. This process, as we have seen, is the 

 source of a constant nitrogen loss, causing the nitrogen com- 

 pounds to be deprived of oxygen and to be reduced to simpler 

 and simpler conditions, until there is finally produced ammonia, 

 which, as a gas, passes into the atmosphere, or nitrogen, which 

 is dissipated in a similar way. This denitrification takes place 

 in the soil at all times, though probably it is not very vigorous 



