176 



BACTERIA AND SOIL FERTILITY 



bacteria which make it possible for the alfalfa to obtain nitrogen 

 from the air. This being the case, a field was selected which had 

 not grown alfalfa and which did not contain the symbiotic nitro- 

 gen-gathering bacteria. This was seeded to alfalfa and one-half 

 of it inoculated with the legume microorganism. To some of 

 the plots were added lime and phosphorus to make certain that 

 these were not the limiting factors. The results obtained are 

 given below: 



Plot 



Treatment 

 Applied 



Pounds 



in Crop 



Pounds Nitrogen 



Mo, 



Dry Matter 



Nitrogen 



Fixed by Bacteria 



la 



None 



1,180.0 



21.81 





lb 



Bacteria 



2,300.0 



62.04 



40.23 



2a 



2b 



Lime 



Lime, bacteria 



1,300,0 



2,570.0 



26.20 

 68.02 



41.82 



3a 



3b 



Lime, phosphorus 



Lime, phosphorus, bacteria 



1,740.0 

 3,290.0 



35-40 

 89.05 



i^M 



It is evident from these results that the alfalfa has obtained 

 from forty to fifty-three pounds of nitrogen from the air, de- 

 pending upon the treatment. There was slightly more than one- 

 third as much nitrogen in the alfalfa crop from the uninoculated 

 than in the inoculated. Therefore, it is evident that the alfalfa 

 in these plots had obtained one-third of its nitrogen from the soil 

 and two-thirds from the air. Now, nitrogen is required by the 

 root for its growth as well as for the growth above the ground, 

 and we have every reason for believing that the root also would 

 obtain it in the same proportion from air and soil as did the hay 

 crop. 



Distribution of 'Nitrogen in Legumes. — If we examine dry 

 matter and total nitrogen occurring in the roots and stalks of 

 alfalfa we should be able to decide whether more nitrogen is 

 being returned to the soil in the roots and residues than is re- 

 moved from the soil by the growing plants. 



