128 



Journal of Agricultural Research 



Vol. XVI, No. 4 





CaCOs 



/rc/ 





CaC/^ } 



CaStZ 



Fig 



ill 



2i>. 



quired to produce the maximum effect vary greatly with the salt. These 



facts are summarized in figures i 

 and 2. 



Only 6 of the compounds tested, 

 sodium sulphate, sodium carbon- 

 ate, potassium sulphate, potas- 

 sium carbonate, calcium carbon- 

 ate, and ferric nitrate , failed to 

 increase the nitric-nitrogen con- 

 tent of the soil. The i8 others 

 all increased the nitric-nitrogen 

 content of the soil. There is no 

 correlation between the stimula- 

 tion of the ammonifying and 

 nitrifying processes of the soil. 

 This is remarkable when we re- 

 member that the speed of the 

 latter is undoubtedly controlled 

 and dependent upon the other. 

 And the results herein reported 

 probably indicate that there are 

 other side reactions taking place 

 which are influenced by these 

 salts but which are not measured 

 by these methods. 



Averaging the molecular 

 weights for the 12 compounds 

 acting as the strongest stimu- 

 lants, we find them to be con- 

 siderably lower than the average 

 molecular weight of those which 

 exert little stimulating influence. 

 We really find some of the com.- 

 pounds with the lowest molec- 

 ular weight — for instance, 

 sodium chlorid — the greatest 

 stimulants. Hence, it would 

 seem thatGrutzer's generalization 



\ 



pjlfcj^^ for animal stimulants does not 

 ^ hold for either t«he ammonifying 



Some of 



-Graphs showing molecular concentrations at 

 which the highest stimulation is noted 



or nitrifying organisms, 

 the strongest stimulants for plants, 

 sodium chlorid and calcium sul- 

 phate, increase to the greatest extent the nitric-nitrogen content of the 

 soil. Therefore it is certain that the increased plant growth is due to a 



