62 
Journal of Agricultural Research 
Vol. XXVIII, No. 1 
Table XII .—The effect of dicyanodiamid upon the ammonification of urea 
Treatment (mgm. N per 250 gm. soil) 
1 day 
3 days 
10 days 
Ammonia 
mgm. N 
Urea 
as am¬ 
monia 
mgm. N 
Ammonia 
mgm. N 
Urea 
as am¬ 
monia 
mgm. N 
Ammonia 
mgm. N 
Urea 
as am¬ 
monia 
mgm. N 
Soil alone...... 
0.83 
0.65 
0.54 
Urea 26.15..... 
28.43 
32.98 
32.33 
22.37 
o 2L 83 
Dicyanodiamid 13.06. . 
1.40 
2.10 
2.85 
Dicyanodiamid 26.12 
1.88 
2.63 
3.33 
Dicyanodiamid 52.24. 
2.10 
3.95 
3.81 
Dicyanodiamid 104.50.... _ 
1.88 
3. 73 
3. 77 
Dicyanodiamid 156.75 
1. 66 
2. 45 
3.38 
Dicyanodiamid 209 . . 
1. 62 
2.98 
3. 33 
Dicyanodiamid 13.06 and urea 26.15. 
28. 25 
26.85 
34.65 
32. 55 
38. 07 
35. 22 
Dicyanodiamid 26.12 and urea 26.15_ 
28.64 
26.76 
34. 70 
32.07 
38. 77 
35. 44 
Dicyanodiamid 52.24 and urea 26.15. 
27.81 
25.71 
36.14 
32.19 
37.28 
33.47 
Dicyanodiamid 104.50 and urea 26.15.. 
27. 59 
25. 71 
36.49 
32.76 
39.17 
35. 40 
Dicyanodiamid 156.75 and urea 26.15_ 
26.06 
24.40 
33.91 
31.46 
34. 34 
30.96 
Dicyanodiamid 209 and urea 26.15... 
27.15 
25. 53 
34.96 
31.98 
35.09 
31.76 
<* A nitrate determination made on this sample showed 14.26 mgm. nitrate nitrogen This rapid con¬ 
version of the urea into nitrates accounts for the low percentage of ammonia at this period. 
THE EFFECT OF GUANYLUREA SULPHATE UPON THE RATE OF AMMONIFICATION 
AND NITRIFICATION OF UREA 
The figures reported in Table IX showed that guanylurea sulphate retarded 
nitrification but to a lesser extent than did dicyanodiamid. In order to obtain 
further data upon this material a more extensive set of experiments was carried 
out to determine the effect of guanylurea sulphate upon both ammonification and 
nitrification. The guanylurea sulphate used was very carefully prepared and 
extracted with acetone until no trace of dicyanodiamid could be detected. Both 
the urea and guanylurea were added in solution to 250 gm. samples of soil con¬ 
taining no calcium carbonate. 
Nitrates and ammonia were determined on the same sample, the reduction 
method being used for the nitrate determinations. In the mixtures containing 
guanylurea sulphate this compound was removed by precipitation with silver 
sulphate and potassium hydroxid before analyzing for nitrates. The data are 
given in Table XIII. . Figure 11 was based upon these results. , 
It will be seen that guanylurea sulphate, in the concentrations used in the 
above experiments, had very little if any effect upon the rate of conversion of 
urea to ammonia in the soil but it did markedly slow down the nitrification of 
this material. The higher the concentration of guanylurea sulphate the greater 
was the inhibiting effect but it was not nearly as great as in the case of dicy¬ 
anodiamid. Where guanylurea sulphate was applied singly there was no ammonia 
accumulation as in the case of dicyanodiamid (Table X) but the material did 
slowly break up into ammonia. The small quantity formed was converted into 
nitrates almost immediately. Comparing the results of Table XIII with those 
of Table X it will be seen that while dicyanodiamid is converted into ammonia 
fairly rapidly a very small amount of the material will prevent the oxidation of 
the ammonia to nitrates. On the other hand, guanylurea ammonifies only very 
slowly but it is much less toxic to the nitrifying organisms. From these results 
we would conclude that both of the compounds, particularly dicyanodiamid, are 
undesirable in soils. However, it should be emphasized that since such exceed¬ 
ingly large percentages of guanylurea sulphate are required to appreciably slow 
up nitrification there is little probability that injury would be observed under 
practical conditions. 
