65 



By referring to Table I it will be seen that there were 93 soils examined 

 and of these 88 were in pairs, that is, consisting of a virgin and cultivated 

 sample. From these 44 pairs, 26 gave a higher fixation by the cultivated 

 and in 18 the virgin soil excelled in the addition of nitrogen. The average 

 increase where the cultivated soils were highest was 3.98 mgs. and where the 

 virgin samples excelled the average gain was 2.08 mgs. The total nitrogen 

 fixed by the virgin samples was 331.66 mgs., and that fixed by the cultivated 

 samples was 389.74 mgs., or a total increase of 58 mgs. Table II sum- 

 marizes these several points: 



TABLE II. Giving the Comparative Results of Nitrogen Fixation by 

 44 Virgin and 44 Cultivated Soils. 



Number of Pairs in which Cultivated Soils excelled 26 



Number of Pairs in which Virgin Soils excelled 18 



Average Increase where Cultivated Soil excelled _ 3.98 mgs. 



Average Increase where Virgin Soil excelled 2.08 " 



Total Nitrogen fixed by Cultivated Soils 389.74 " 



Total Nitrogen fixed by Virgin Soils 331.66 ' ' 



Original Nitrogen in Cultivated Soils 455.25 ' ' 



Original Nitrogen in Virgin Soils : 513.38 " 



The superiority of cultivated soils in fixing nitrogen is strongly indi- 

 cated by results from the foregoing table. They are in accord with the 

 recent findings of Greaves 1 though not so pronounced, due perhaps to very 

 dissimilar conditions. A substantial majority of the soils examined showed 

 a higher fixing power by the cultivated samples than by the virgin, and the 

 increase where noted in cultivated soils was relatively much higher than 

 when it took place in the virgin soils. These results are without regard to 

 any factor save that of cultivation and for this reason are all the more sig- 

 nificant. They represent tests from a large number of soils of varying tex- 

 ture, collected from definitely separated areas, and the cultivated samples 

 had experienced a variety of types of cultivation. Notwithstanding these 

 facts the evidence which points to the advantages of cultivation in develop- 

 ing the Azotobacter flora is unmistakable. This would seem at least one 

 indubitable stimulation which free nitrogen fixation may receive. 



An interesting point is the higher original nitrogen content of the virgin 

 soils as compared with the cultivated ones. The analyses of 44 virgin sam- 

 ples showed that in 29 of that number there was more total nitrogen than in 

 the- corresponding cultivated samples, and of the 18 virgin samples which 

 excelled the corresponding cultivated ones in fixation, 15 had also more total 

 nitrogen. Yet it is difficult to trace from the foregoing results any relation- 

 ship between the amount of nitrogen in a soil and that which it adds by 



^Greaves, J. E. A study of bacterial activities in virgin and cultivated soils. Cent. f. Bakt. 

 II. Abt. Bd. 41., p. 444. 



