Jan. 27, 1919 



Influence of Salts on Nitric Nitrogen in Soil 



125 



fourth. But even in the presence of large quantities of this salt there is 

 a notable disappearance of nitric nitrogen from the soil. 



Ferric nitrate is peculiar, in that it fails to stimulate in any of the con- 

 centrations tested, and there is a gradual increase in toxicity from con- 

 centration to concentration. However, even where the largest quantity 

 of iron nitrate was added, there was no loss of nitric nitrogen from the 

 soil. 



The occurrence of the negative results where the sodium, potassium, 

 calcium, magnesium, and manganous nitrate are added to the soil raises 

 the question, Has denitrification taken place or does it stimulate other 

 bacterial activities so that the nitric nitrogen is rapidly transformed into 

 protein nitrogen ? ^ 



In order to answer this question, a set was prepared in which the vari- 

 ous salts were added to the soil and incubated for 21 days, and the total 

 nitrogen determined. The results are given in Table XIV. Each is the 

 average of four determinations. 



Table XIV. — Quantity of nitrogen obiaitied from loo gm. of soil receiving various 



treatments 



Treatment. 



Dried blood, no nitrate 



Dried blood, 84.06 mgm. of nitric nitrogen as sodi- 

 um nitrate 



Dried blood, 84.06 mgm. of nitric nitrogen as cal- 

 cium nitrate 



Dried blood, 84.06 mgm. of nitric nitrogen as ferric 

 nitrate 



Dried blood, 84.06 mgm. of nitric nitrogen as mag- 

 nesium nitrate 



Dried blood, 84.06 mgm. of nitric nitrogen as man- 

 ganous nitrate 



Dried blood, 84.06 mgm. of nitric nitrogen as potas- 

 sium nitrate 



Nitrogen in 



100 gm. of 



soil. 



Mgm. 

 333-9 



419-3 

 460.5 



455- o 

 466.5 



443- I 

 412. o 



Excess in 

 nitrate- 

 treated soil. 



Mgm. 



85-4 



126. 6 

 121. I 

 132.6 



109. 2 

 78.1 



Gain or loss 

 in nitrogen 

 over soil re- 

 ceiving no 

 nitrate. 



Mgm. 



1-34 

 42-54 

 37-04 

 48-54 

 25. 14 



- 5-96 



It is evident from these results that the loss of nitric nitrogen from 

 this soil is not due to denitrification, for we find in every case, with the 

 exception of where the potassium nitrate was added to the soil, that 

 there was a gain of combined nitrogen. This is remarkable, for we have 

 here a soil which was low in nitrogen but to which had been added 2 per 

 cent of dried blood greatly stimulated in its nitrogen-fixing powers. 

 The quantity of nitrogen fixed by this soil on the addition of the various 

 nitrates in some cases is from four to eight times that normally fixed 

 by the soil. Whether the azofiers would continue to fix nitrogen at this 

 speed is doubtful, but experiments are under way in this laboratory to 

 decide this point. If they will, it opens up an interesting and practical 

 field for investigation. 



