112 



Journal of Agricultural Research 



Vol. XVI, No. 4 



normal. But when an equivalent quantity of sodium in the form of the 

 nitrate is added, the nitrifying powers are reduced to one-fifth. 



The work was so planned that equal molecular proportions of the 

 various salts could be compared as shown in Table III. 



Table III. — Percentage oj nitric nitrogen formed in lOO gm. of soil containing 2 gin. 

 of dried blood and varying amounts and forms of sodium salts in equal molecular pro- 

 portions 



[The untreated soil is taken as loo per cent] 



Fraction of rnolecular weight in loo gin. of soil. 



None .... 

 156X10""' 

 312X10"^ 

 625X10"^ 

 125X10"® 

 25X10"* 

 SXio-* 



I X 10-3 



2X10-3 

 4X10-3 



Percentage of nitric nitrogen formed in presence of — 



Sodium 

 chlorid. 



100. O 

 102. 4 



102. 5 

 100. 6 



103. I 

 114. 7 

 139.6 

 142. 7 

 136. 2 



57-5 



Sodium 

 sulphate. 



100. O 

 60. 2 



57-1 

 86.2 

 74.0 

 55-1 

 65-4 

 63.2 

 63. o 

 50.8 



Sodium 

 nitrate. 



92 



94.4 

 lOI. o 



75-9 

 71. 6 

 69.4 

 48.0 

 17. I 



Sodium 

 carbonate. 



79- 

 76. 



94. I 



79-4 

 73-5 

 76-5 

 58.8 

 58.8 



Sodium chlorid, which has the lowest molecular weight, is the least 

 toxic, whereas sodium nitrate, with the next lowest, comes next in order 

 of toxicity. It is, therefore, quite evident that the toxicity of the sodium 

 salts varies with the electro-negative ion with which sodium is combined 

 and must be due to a physiological influence exerted by it upon the 

 protoplasm of the organisms and not due to a direct osmotic effect. 



INFLUENCE OF POTASSIUM SALTS 



The compounds used in the potassium series were the chlorid, sulphate, 

 nitrate, and carbonate. The concentrations were the same as those used 

 in the sodium series. The results, as reported in Table IV, are the 

 average of four or more closely agreeing determinations. 



Potassium chlorid and potassium nitrate are the only potassium salts 

 which yielded a stimulation with the nitrifying organisms. But after 

 the stimulating concentration is exceeded these compounds rapidly in- 

 crease in toxicity, so that by the time a concentration of 2,346 p. p. m. 

 of potassium in the form of the chlorid has been added to the soil, the 

 nitric nitrogen present had been reduced to 5.23 per cent. Where a 

 similar quantity of the nitrate was added, there was a marked loss of 

 fiitrates. 



Potassium sulphate was found to be toxic in the lowest concentration 

 tested, but the toxcity does not increase as rapidly with the increased 

 concentrations of this salt as it does with those salts which are stimulants. 

 For it is only when 1,564 p. p. m. of potassium in the form of potassium 

 sulphate has been added to the soil that we find the nitric-nitrogen ac- 

 cumulation reduced to one-half normal. 



