340 ANNUAL REPORT OF THK Off. Doc. 



due to definite organisms in the soil, the laws which control nitrifica- 

 tion are simply the laws which control the life and development of 

 said organisms. 



If a soil be wet with a one per mille solution of bichloride of 

 mercury, no nitrification can take place; firstly, because the mercury 

 compound has destroyed the life of all nitrifying as well as other 

 organisms, and secondly, because the presence of such a salt in the 

 soil will prohibit the development of all nitrifying ferments which 

 come after. 



Again, if a soil be heated above a certain temperature, all nitri- 

 fying ferments will be destroyed and nitrification will cease. 



Chloroform, formaldehyde gas, sulphurous acid gas, etc., passed 

 through a layer of soil will, on the same principle, prevent further 

 nitrification. 



These, however, are all agencies implying the total destruction of 

 the nitrifying ferments. In addition to these there are certain con- 

 ditions which, while they do not annihilate the life of the nitrifying 

 organism, are yet either favorable or unfavorable to their normal 

 development. These conditions the agriculturist must understand, 

 in order to control the nitrifying process in the soil. 



(c.) Conditions Afecting Nitrification. 



Quantity of Organic Matter or Humus ^V^ the Soil. 



It has already been stated that the nitrifying organism will not 

 grow in a medium containing any considerable amount of soluble 

 organic matter. 



When sewage is applied to land nitrification cannot, therefore, 

 begin until after the ordinary putrefying and ammonifying bacteria 

 have decomposed much of the organic matter and rendered the soil 

 water a fit pabulum for the development of nitrifying ferments. 



In a 12 per cent, solution of urine, according to Warrington,^^ nitri- 

 fication did not begin until about ninety days, and then only after 

 447 milligrams of ammonia per litre had been produced by the de- 

 composition of the organic matter present. 



For this reason sewage when applied to land should be used 

 cautiously and not too frequently, otherwise the soil will become so 

 rich in soluble organic matter as to hinder nitrification and thus 

 render the large accessions of nitrogenous food useless. 



Thus a soil too rich in humus is an unfavorable nitrifying ground 

 up to the limit when nitrification ceases. Just what this limit is, is as 

 yet unknown. Wiley^^ mentions a soil from Florida containing over 

 80 per cent, of organic matter, and less than 10 per cent, of sand and 

 other mineral matter, which was found to be entirely free from nitri- 



