76 



The Effect of Combinations of Non-Nitrogenous 

 Compounds Toxic to Plants in Solution Cultures, 

 ON THE Nitrification of Dried Blood, Pyridine, Etc. 



A study of the effect of one, or the combined effect 

 of two, or three, non-nitrogenous compounds on nitri- 

 fication was made in 1915, using Norfolk sandy loam 

 soil similar to that used in other tests reported on the 

 previous pages. The data obtained are presented in 

 table VI. 



Table VI. — The Effect of Combinations of Non- 

 Nitrogenous Compounds on the Nitrification 

 of Dried Blood, Pyridine, Etc. Nitrates 

 Expressed as p. p. m. of Dry Soil. 



In the soil otherwise untreated each of the com- 

 pounds was nitrified, the highest nitrate content being 

 found in soil treated with guanidine carbonate, and the 

 lowest, in soil treated with quinoline. 



By the addition of vanillin, nitrification of all com- 

 pounds was seriously reduced, with the exception of 

 piperidine, from which more nitrates were formed with 

 vanillin than without it. 



The combined action of vanillin and cumarin was to 

 inhibit completely the* nitrification of all compounds. 

 Dried blood was slightly nitrified in the presence of 

 these two non-nitrogenous compounds, where lime was 

 added; unfortunately, lime was not used in connection 

 with the other nitrogenous substances. 



In the presence of vanillin, cumarin, and dihydroxy- 

 stearic acid, nitrification was inhibited in all cases 

 except in the soil treated with dried blood, in which 

 there was found a very small amount of nitrates. In 

 the limed series, however, a varying quantity of ni- 



