CHEMISTRY OF FERTILIZERS 13 



55 degrees C., 37 degrees C., being that at which 

 they are most active. Darkness is favorable 

 to their development. The process of nitrifica- 

 tion is but one phase of the general oxidizing 

 action which is associated with the growth of 

 these bacilli. Thus they are capable of converting 

 iodides into iodates. " Denitrifying " organisms 

 appear also to exist in the soil, capable of reducing 

 nitrate even to free nitrogen. These become active 

 when the soil is water-logged, and are inimical to 

 plant life. 



The process of nitrification is so rapid that 

 ammonium sulphate is scarcely less readily assim- 

 ilated than is sodium nitrate. There is, however, 

 a certain amount of difference in the quantity 

 of certain crops when manured with nitrate and 

 ammonium sulphate respectively, which will be 

 found as set forth. Another difference in their 

 action is on the soil itself; before the nitrifica- 

 tion of ammonium sulphate can be completed, 

 the sulphuric acid must be removed by a base 

 e.g., lime in the soil, and a further quantity of 

 base will be required by the nitric acid when formed. 



Common salt has an indirect fertilizing value 

 which is mainly due to the fact that it has the 

 power of changing unavailable forms of plant 

 food, especially potash, into available forms. 



It should be kept in mind that these stimulant 

 fertilizers, that is, gypsum (or plaster), lime, and 

 salt are not used for the plant food contained 

 in them; hence, as used, they do not furnish 



