H. B. Hutchinson 



107 



although it possessed a much higher nitrogen content. This is possibly 

 due in the first place to the numerical superiority of Azotobacter 

 already present in the soil and may also be connected with the effect 

 exerted by traces of humates and of iron compounds on nitrogen fixation 

 noted by other workers. 



The gains of nitrogen per gram of substance suppUed are given in the 

 following table, from which it is seen that the returns from the use of 

 sugar are somewhat higher than those obtained by the addition of haj' 

 dust. On the other hand, it must be recognised that the whole of the 

 carbonaceous compounds in the latter material would probably not be 

 completely oxidised within the course of the experiments. The actual 

 return is consequently greater than would appear from the data given. 



Table V. 

 Utilisation of Hm/ and Sugar for Nitrogen Fixation. 



Treatment 



Sand alone 



Sand + hay (sterilised) 



Sand + hay + putrefactive organisms 



Sand + hay + putrefactive organisms + Azotobacter 



Sand + sugar (sterilised ) 

 Sand + sugar + Azotobacter ... 



Less 148 mgrms. supplied in hay. 



The Influence of Sugar and Plant Residues on Losses of Soil 



Nitrates. 



During the course of the work described in the preceding pages, a 

 number of instances occurred in which the possible operation of nitrogen 

 fixation processes was effectively masked by the entrance of changes 

 which were adverse to plant growth. This was evident in the earlier 

 stages of the pot experiments but attained greater prominence in the 

 field work when starch or sugar was apphed to the plots in spring, and 

 especially when a minimum interval elapsed between the application and 

 the sowing of the crop. This is seen in the following summarv of the 

 yields of plot 4. 0. 



Time of application 



March 6th Feb 19th Feb. 4th Jan. 17th Sept. (mean) 

 Relative yields (cont-ol = 100) nil 71 77 91 137 



