Apr. 5,1924 
Studies with Cyanamid 
61 
THE EFFECT OF DICYANODIAMID UPON THE RATE OF AMMONIFICATION OF UREA 
These experiments were planned to determine if dicyanodiamid prevents or 
retards ammonification, as was found to be true in the case of nitrification. 
The dicyanodiamid and urea were added in solution to 250 gm. samples of soil. 
No calcium carbonate was used. The results of the ammonia determinations 
are given in Table XII and shown in part in figure 10. 
From the data it will be seen that concentrations of dicyanodiamid as high 
as 315.2 mgm. per 250 gm. of soil had no appreciable effect upon the rate of 
ammonification of urea. The recovery of more than 100 per cent of the added 
urea nitrogen in most of the analyses indicates that the added nitrogenous 
compounds accelerated the ammonification of the organic soil nitrogen. Another 
possible explanation is the fact that soluble salts tend to accumulate at the 
surface of a soil layer due to evaporation, and it is quite possible that in obtain¬ 
ing the 25 gm. of soil from the 250 gm. samples the mixture was not as thoroughly 
mixed as it should have been. This would mean that too large a portion of 
the surface soil was included in the samples analyzed. Regardless of the dis¬ 
crepancy, it is quite evident that dicyanodiamid is not especially toxic, if at all, 
to the ammonifying organisms. In a fertile soil containing appreciable dicyano¬ 
diamid we would therefore expect to find an ammonia accumulation and prac¬ 
tically no nitrates. 
