114 Deromposition of Cyanamide and Dicyanodiamide 



Our investigation has shown that the two compounds behave very 

 difEerently in the soil. Cyanamide readily breaks down yielding ammonia 

 which then nitrifies in the usual way. The evidence indicates that the 

 conversion of cyanamide nitrogen into nitrate is practically quanti- 

 tative, irrespective of the nature of the soil. Cyanamide therefore 

 serves as a valuable fertiliser. Parallel tests made in the laboratory and 

 in the pot-culture house showed that the amount of nitrate accumulating 

 in the soil to which cyanamide is added is identical with the amount of 

 nitrogen taken up by the plants growing in the soil containing an equal 

 amount of cyanamide and under generally similar conditions. 



No evidence was obtained to support the views held by Immendorii CJ) 

 and Kappen (lO) as to the production of dicyanodiamide from cyanamide 

 in poor soils and those of an acid nature of low bacterial activities. 



On the other hand, our experiments have demonstrated that di- 

 cyanodiamide not only fails to act as a nutrient but is actually toxic to 

 plants. Small quantities (18 mgs. N per kilo soil) in pot-culture do not 

 appreciably injure the higher plants, but still smaller quantities exerted 

 no stimulating influence on growth ; this affords an additional corrobo- 

 ration of Brenchley"s(ii) contention that poisonous substances do not 

 necessarily act as stimulants when supplied in sufficiently small doses. 



When dicyanodiamide is mixed with cyanamide it greatly reduces 

 the amount of nitrate produced from the cyanamide. Careful inv^estiga- 

 tion, however, brought out the striking fact that the plant succeeded in 

 obtaining more nitrogen from the mixture than corresponded with the 

 nitrate produced, thus: 



% added N removed in crop % added N nitrified 

 Cyanamide 3 parts ) „„ 



Dicyanodiamide 1 part J 



Cyanamide 1 part ) „ 



Dicyanodiamide 3 parts ) 



Further investigations showed that the dicyanodiamide had not 

 prevented the formation of ammonia from cyanamide; indeed it had 

 hardly aft'ected this reaction, but it had almost entirely inhibited the 

 subsequent transformation of ammonia into nitrate. 



The dicyanodiamide was found to be toxic to the sensitive nitrifying 

 organisms, so that it stops the decomposition of cyanamide at the 

 ammonia stage and inhibits the formation of nitrates. 



Thus the addition of dicyanodiamide to cyanamide results in an 

 accumulation of ammonia in the soil which does not undergo the normal 

 oxidation to nitrates but persists as ammonia. 



