14 Influence of Ar senk in Solls [Oct. 



Both ammonification and nitrification were greatly stimulated 

 by arsenic trisidfide. It is likely that the sulfur played some part in 

 this result. Demolon-^ attributed much of the fertilizing action of 

 sulfur to its action on bacteria. The results which Russell and 

 Hutchinsons^ obtained with calcium sulfide are interesting in this 

 connection, They found that after thirty days there were five times 

 as many organisms in soil to which calcium sulfide had been added 

 as in the untreated soil, and that the yield of ammonia and nitrates 

 in this time was one third greater in the treated soil than in the un- 

 treated soil. These results show considerable similarity to the data 

 reported here for arsenic trisulfide ; and most of the results obtained 

 in this study may be interpreted by their theory^^ — that the soil con- 

 tains another group of organisms which are detrimental to bacteria. 

 If this theory be accepted, we must conclude that the soil bacteria 

 are much more resistant to arsenic than are these other organisms, 

 and that the soil organisms are able to function in the presence of 

 very much larger quantities of arsenic than is this other class of 

 organisms. For, while the antiseptics used by Russell and Hutch- 

 inson in their experiments were subsequently removed, this was not 

 the case with the arsenic in this work. As large a quantity of 

 water-soluble arsenic was found in the soil at the end as at the 

 beginning of an experiment. Some of the observed Stimulation 

 was doubtless due to copper, lead, zinc, and sulfur, or whatever 

 other foreign material was present in the insecticides. The con- 

 stant ocurrence of a Stimulation in all the series points conclu- 

 sively, however, to the fact that arsenic in some concentrations stim- 

 ulates bacterial action. It must evidently occur in soil in large quan- 

 tities before it becomes very toxic to the soil organisms. 



IV. SUMMARY 



One hundred parts per million of sodiiim arsenate may be ap- 

 plied to a soil rieh in calcium and iron without materially decreasing 

 the ammonifying or nitrifying powers of that soil. Smaller quan- 

 tities may stimulate these activities. 



22 Demoion : Compt. rend., 1913, elvi, p. 725. 



23 Russell and Hutchinson : Jour. Agr. Sei., 1913, v, p. 173. 

 2* Russell and Hutchinson: Ibid., 1909, iii, p. m. 



