G. A. CowiE 115 



In like manner the addition of dicyanodiamide to soil also containing 

 amnioniuni sulphate stops the oxidation normally brought out by the 

 nitrifying organisms. 



It does not appear, however, that dicyanodiamide has so drastic an 

 effect on the other organisms of the soil, especially on those concerned 

 in the decomposition of protein. It hardly affects the numbers developing 

 on gelatine plates or the rate and extent of the decomposition of dried 

 blood. 



The Production of Ammonia and Nitrate from 

 Cyanamide and Dicyanodiamide. 



The cumulative evidence from the Nitrification Tests (plotted in 

 Fig. 1) clearly indicates that the change of cyanamide nitrogen into 

 nitrate is almost quantitative and closely approximate in this respect 

 to ammonium sulphate. The nitrification of cyanamide, however, is 

 appreciably slower than that of the latter compound, especially in the 

 initial stages. This would be accounted for by the time required for 

 the primary decomposition of cyanamide into ammonia. 



Dicyanodiamide, on the other hand, has given practically no evidence 

 of nitrification even after three months. 



Cyanamide and ammonium sulphate show a general similarity. 

 The former lags distinctly for the first 15 days, but it then gains sub- 

 stantially and after 35 days runs appreciably close and nearly parallel 

 to the other. 



The mixtures of cyanamide and dicyanodiamide show less nitrifica- 

 tion than was expected from the cyanamide present, while the di- 

 cyanodiamide gave no indication of being nitrified at all. This result 

 was obtained both with the heavy Rothamsted and the light Woburn 

 soil (see Table V). 



Crof Results. 



In the vegetation experiments cyanamide produced a consistently 

 beneficial effect on plant growth and gave results substantially in accord- 

 ance with the extent of its nitrification as shown by the laboratory 

 tests. In the Rothamsted soil it exerted no adverse action on germina- 

 tion in any of the quantities used, but a dressing of 100 mgs. N per 

 kilo soil caused some retardation in the Woburn soil. It was somewhat 

 slower in action than ammonium sulphate, especially when a small 

 amount of dicyanodiamide was present. Its nutrient effect, however, 

 proved approximately equal. This is also in agreement with the 



8—2 



