106 AGRICULTURAL BACTERIOLOGY 



ditions in the soil essential for the process do not obtain 

 for any length of time. If nitrates were added to a rich 

 soil or were applied simultaneously with barnyard manure, 

 a portion of the nitrogen might be lost; but in ordinary 

 soils no great loss of nitrogen can occur because of this 

 process. 



Many soil bacteria can obtain the nitrogen needed to 

 build their cells from nitrates. If any considerable amount 

 of growth of the organisms takes place at the same time 

 the demand of the crop for nitrate is greatest, the crop may 

 be limited in its growth, since nitrogen is most frequently 

 the limiting element. There would be the same objection 

 to these bacteria as to weeds among a cultivated crop, 

 namely, the removal of food that might otherwise be used 

 by the crop. These bacteria ultimately die and the nitro- 

 gen is ammonified, so they do not permanently remove the 

 nitrogen from the soil, but merely take it temporarily from 

 the reach of the plant. 



