G. A. CowiE 



n: 



When cyiiiiaiiiide alone is used there is a very close relationship 

 between the amount of nitrogen converted into nitrate in the laboratory 

 tests and the amount of nitrogen assimilated by the plant in the pot- 

 culture tests. But when dicyanodiamide is present this close relationship 

 no longer holds. Assuming that the nitrification of the soil organic 

 matter is not materially aii'ected by the cyanamide, the following 

 quantities of nitrogen were assimilated in the mustard pot experiments 

 and nitrified in the laboratory tests: 



100 mgs. N per kilo 

 soil applied 



Cyanamide alone 

 Cyanamide 3 parts ) 



Dicyanodiamide 1 part ) 

 Cyanamide 1 part 1 



Dicyanodiamide 3 parts J 

 Dicyanodiamide alone ... 



From the mixtures of cyanamide and dicyanodiamide the plants 

 have taken up substantially more nitrogen than there was nitrate 

 produced. The comparatively small amount of nitrification which has 

 occurred in these cases suggested some adverse effect of the dicyanodi- 

 amide on the nitrification of the cyanamide. 



The retardation of the nitrification of cyanamide in the presence of 

 dicyanodiamide was then investigated using cyanamide alone, 50 mgs. 

 N per kilo soil, and an equal quantity of cyanamide in addition to a 

 small amount (15 mgs. N per kilo soil) of dicyanodiamide. The results 

 show a marked depressing effect of the dicyanodiamide on the nitrifica- 

 tion of the cvanamide. 



N as Nitrate present 

 per million dry soil 



N as NH3 present per 

 million dry soil 



At 

 start 



15-9 



After 

 6 days 



210 



25-9 



After 

 18 days 



21-5 



00-2 



After 

 42 days 



25-6 



74-2 



After 

 102 days 



310 



810 



After 

 18 days 



4 



3 



After 

 42 days 



5 



— 200 



19-9 



28-4 



56-3 



23-5 



20 



After 

 102 days 



1 



1-5 



10-8 



Control (no N) ... 

 Cyanamide alone 

 Cyanamide + ^ 



dicyanodiamide J 



Added 50 mgs. cyanamide N per kilo soil = 00 parts of N per inillion dry soil. 

 15 mgs. dicyanodiamide N per kilo soil. 



Nitrification of the cyanamide has been almost entirely inhibited by 

 the dicyanodiamide for 42 days, after which it proceeds only at a slow 

 rate and is not complete after 162 days. There is, however, a notable 

 production of ammonia from cyanamide in the presence of dicyanodi- 



