214 



SYSTEMS OF PERMANENT AGRICULTURE 



TABLE 33. FIXATION OF NITROGEN BY ALFALFA IN FIELD CULTURE 

 Illinois Experiments on Common Prairie Land 



occurred during the progress of the experiment, these amounts 

 might understate the effect of the bacteria. It is very probable, 

 however, that the increased root development, induced by remov- 

 ing the nitrogen^limit in plant growth, would make it possible for 

 the infected plants to secure somewhat more soil nitrogen than 

 otherwise. (Note the effect of phosphorus in the record.) How- 

 ever, this, too, should perhaps be placed to the credit of the bac- 

 teria, even though it is not atmospheric nitrogen, because if such 

 nitrogen existed in the soil solution, it would soon have been lost 

 in drainage waters if not taken up by the enlarged root system of 

 the growing crop. 



Slightly more than one third of the total nitrogen contained 

 in the crop from the inoculated unfertilized plot was secured from 

 the soil, with larger proportions and larger actual amounts for the 

 other plots. 



It should be borne in mind that nitrogen is required for root 

 growth as well as for growth above ground, and that three other 

 crops of alfalfa were cut from these plots during the season, this 

 cutting having been made on May 28. Evident cross inoculation 

 occurred before a second cutting was obtained; but the data given 

 in Table 33 indicate that plot ib secured about 172 pounds of 

 nitrogen from the air during the season, the yield of air-dry hay 

 having been 2563 pounds for the first cutting and 10,980 for the 



