12fi Decomposition of CijananiitJc (oul Diciianodiamide 



of the organic matter in the soil would proceed to the same extent in 

 the treated as in the control soils: the amount of soil organic matter 

 nitrified in the treated soils might conceivably depend on the relative 

 availability of the added nitrogen. In cases such as series I and II in 

 the Rothamsted soil, where the control has remained more or less 

 constant throughout, the matter is simplified and the percentages 

 might then be approximately determined by deduction of the highest 

 control as has been done in the series in question. In other cases a 

 general comparison only can be made between the amounts of nitrates 

 formed in the control and the experimental sets. 



The Determination of Ammonia in the Soil. 



The amounts of ammonia in the soil were determined by Folin's 

 aeration method, which has been modified and adapted for soil investi- 

 gation by Potter and Snyder (26). It was essential to success that the 

 method should entail no formation of ammonia from the cyanamide or 

 dicyanodiamide. Neither of these substances, however, gave evidence of 

 any appreciable hydrolysis under the conditions in question. Further, 

 the amount of ammonia found by this method in the Rothamsted soil 

 satisfactorily agreed with that recovered by extraction with dilute 

 hydrochloric acid. The results were: 



60 parts N per million dry soil added 



N recovered per million 

 dry soil 



Soil alone (aeration) 



(extraction with dilute HCl) 

 y oil and cyanamide 

 Soil and dicyanodiamide 



Soil and mixture of cyanamide and dicyanodiamide 

 Sou and ammonium sulphate .. . 



The above results show that the cyanamide and dicyanodiamide 

 compounds remain comparatively stable under the conditions of the 

 experiment. A slight tendency to decomposition is evident only with 

 the cyanamide dressing in the Rothamsted soil. The figures for 

 ammonium sidphate reveal the difficulty in recovering the whole of 

 the ammonia by reason of its absorption and retention by the soil. By 

 adopting, however, the same definite period for aeration duplicate 

 samples were found to give satisfactorily concordant results and con- 

 sistently show an approximate recovery of 60 per cent, of the added 

 ammonia in the Rothamsted soil. 



