NON-SYMBIOTIC NITROGEN FIXATION 147 



aeration are much more nearly ideal in a fallow soil than in a 

 cropped soil. It is just possible that the high fixation noted where 

 wheat is grown continuously may be due to the method in vogue 

 in the arid districts of leaving the greater part of the straw on 

 the soil. This would serve as readily assimilable carbonaceous 

 material for the Azotobacter, Fallowing not only increases the 

 assimilable nitrogen but also the available phosphorus of the soil, 

 a liberal supply of which causes the Azotobacter to utilize its 

 energy more economically. 



How is the Nitrogen Fixed? — How different are the ways 

 of man and the microbe! Man fixes nitrogen by means of a gi- 

 gantic arclight in a chimney through which a current of hot air 

 is blown. The flaming disc has a diameter of seven feet and 

 reaches a temperature in the neighborhood of 6,300 F. The gas 

 which he obtains when dissolved in water yields nitric acid. Or, 

 in another method air is cooled to — 1 94 C, the nitrogen boiled 

 off, mixed with hydrogen in the proportion of l to 3, heated to a 

 temperature of 1,300 C, and then passed over finely divided 

 uranium. There results ammonia. This mixed with oxygen and 

 passed through platinum gauze, yields nitric acid. Thus in all 

 synthetic processes there is used great variations in temperature 

 and huge, complicated, expensive apparatus. 



When the microbe fixes nitrogen there is also a real conflagra- 

 tion in which plant residues act as the fuel and the bacterial 

 body the furnace. But how different are the two ! The microbe 

 is 90 per cent water. It works in the dark, damp, warm soil 

 and generates little heat and no light. We know its end products 

 are not the simple nitric acid, ammonia, or cyanamid but complex 

 proteins. These we know are similar to those found in plants. 

 They are formed from the same blocks. Some are soluble j 

 others insoluble. All are broken down by bacteria and yield food 

 for the higher plants. We do not know the first products which 

 are produced in their formation nor the marvelous way in which 

 the lazy nitrogen is enticed to join hands with carbon, hydrogen 

 and oxygen. We can only surmise that the future will unravel 

 the mystery. But when unravelled, as it surely will be, the 



