NON-SYMBIOTIC NITROGEN FIXATION 149 



that aliiiit neither in the laboratory nor in the field had the ability 

 to fix nitrogen. When Beijernick discovered the free-living 

 aerobic nitrogen fixers, the hope that soil inoculation might be 

 so perfected that it would be beneficial to crops v^as revived, and 

 since that time many investigators have attempted to inoculate soil 

 in order to increase its crop-producing powers but usually with 

 negative results. Some have made great claims for soil inocula- 

 tion. They have found that soils, inoculated with Azotobacter 

 chroococcum and adequately supplied with carbohydrates and 

 lime, show an increase in the number of nitrogen-fixing organ- 

 isms and also an increase in yield. 



There may be a decrease m the crop during the first year when 

 carboyhdrates and Azotobacter are added to the soil with a marked 

 increase in crop during the second and third years. Even then 

 the soil may be left richer in nitrogen than it was at first. 



Effect of Dextrose and Sucrose on the Productiveness and 

 Nitrogen Content of the Soil 



Carbohydrate 

 Added per 

 100 gm, of 



Soil 



None 



2 % Dextrose 

 2 % Sucrose 

 4 % Sucrose 





Crops Obtained 





Total 



Nitrogen 



Removed 



in 



Crop 



Total 

 Nitrogen 

 Left in 



Soil 

 Spring 



igo6 



Oats^ igos 



Sugar-beets^ igo6 



Dry 

 Matter 



Yield of 

 Nitrogen 



Dry 

 Matter 



Yield of 

 Nitrogen 



1 00.0 



3'^'3 

 33-3 



37-7 



lOO.O 



62.5 



S8.7 

 78.1 



1 00.0 



ia6.o 

 179.0 

 283.0 



100,0 

 190.0 

 195.0 

 339'0 



gm. 

 0.5914 

 0.6814 

 0.6800 

 1.0092 



per cent 

 0,093 

 0.105 

 0.105 

 0.119 



Nitrogen 



as 

 Nitrates 

 (:p.p.m,) 



10 



17 

 15 



37 



It is often the case that the addition of starch to a soil during the 

 first year retards plant growth. This injurious action may be 

 due to the increased bacterial activity in the soil brought about 

 by the carbohydrates which injure the roots of the plant by with- 

 drawing oxygen and by forming hydrogen sulfide in the deoxy- 

 genated atmosphere of the soil through the reduction of sulfates 

 by the bacteria. Or what is more likely the increased number of 



