Jan. 37. i9»9 Influence of Salts on Nitric Nitrogen in Soil 1 29 



great extent to the increased available plant food yielded by the accel- 

 erated bacterial activity of the soil. 



The quantity of the salt necessary to produce maximum stimulation 

 varies greatly with the salt. It is usually the case that those compounds 

 which are the greatest soil stimulants must be added in larger quan- 

 tities to produce maximum stimulation than those which are not as 

 active stimulants and which produce their greatest effect at lower con- 

 centrations. 



Fig. 2. — Graphs showing the percentage of stimulation at the above noted molecular concentrations 

 (see fig. i), the untreated soil bclnj counted as producing loo per cent of nitric nitrogen. 



RELATIVE TOXICITY OF THE VARIOUS SALTS 



The salts used in this work may be compared as to toxicity from three 

 viewpoints: First, the lowest concentration of the salt at which a toxic 

 effect is noted toward the nitrifying organisms; second, the molecular 

 concentration at which nitric-nitrogen accumulation is reduced to three- 

 fourths normal; and third, the percentage of nitric-nitrogen produced in 

 the presence of the largest quantity of the various salts, which is 2 X io~^ 

 mole of the salt in 100 gm. of soil. These results are reported in figures 3, 



