130 University of California Fublications in Agricultural Sciences [Vol. 1 



totally different substance from the metals we have studied, it 

 is interesting to compare its effects on the soil tlora with those 

 exercised by copper, zinc, lead and iron. This is especially so 

 since arsenic so frequently occurs with the other elements in 

 soils and in smelter wastes from which it may be transported to 

 agricultural soils. 



In closing this brief review of investigations dealing with the 

 subject of this paper or one allied thereto, it should also be 

 added that some fragmentary information was obtained in the 

 course of other investigations by J. G. Lipman and his asso- 

 ciates" which refers to the effects of CUSO4, and FeSO^ among 

 other compounds on the ammonifying flora of the soil. These 

 results indicate that copper stimulates ammonification very 

 slightly at a concentration of 0.1 per cent, that ZnSO^ gives no 

 stimulation and is toxic at all concentrations, and that FeSO^ 

 at the concentration of 1 mg. per 100 grams of soil gives marked 

 stimulation. 



The Ammonification Experiments 



To a fifty-gram portion of dry soil, one gram of tankage 

 (9.62% N) was added and thoroughly mixed Avith it. Sterile 

 distilled water was then added, to make optimum moisture con- 

 ditions, and also varying quantities of the salts to be tested. 

 The soil, water and salt mixture was thoroughly stirred in the 

 tumbler, the latter covered with a Petri dish cover and incubated 

 for one week at 27° C to 30° C. The results of the ammonia 

 determinations at the end of the incubation period, together with 

 other necessary explanatory data, wull be found in Table 1. The 

 sulfates of the metals tested were employed throughout. It Avill 

 be noted that the results of duplicate determinations are given 

 throughout, averages being omitted since the reader can so 

 readily ascertain them from the data submitted. 



It is at once obvious, from even a casual examination of the 

 data given in Table 1, that none of the metals employed exercises 

 a stimulating effect on the ammonifying flora of the soil employed 

 even at the smallest concentrations (50 p. p.m.). Despite that 



14 N. J. Exp. Sta. Bull. no. 246, p. 32. 



