56 
•Journal of Agricultural Research 
Vol. XXVIII, No. 1 
Table IX.— Comparison of the rates of nitrification of dicyanodiamid, guanylurea 
sulphate, and ammonium sulphate 
16 days 
28 days 
42 days 
70 days 
112 days 
154 days 
210 days 
Treatment (20.9 
mgm. N per 100 
gm. soil) 
Nitrates 
mgm. N 
Increase over 
control 
mgm. 
Nitrates 
mgm. N 
Increase over 
control 
mgm. 
Nitrates 
mgm. N 
Increase over 
c o n t r oi 
mgm. 
Nitrates 
mgm. N 
Increase over 
control 
mgm. 
Nitrates 
mgm. N 
Increase over 
control 
mgm. 
CO 
Zz 
Zz 
r? 
% 
Increase over 
control 
mgm. 
Nitrates 
mgm. N 
Increase over 
control 
mgm. 
Soil, untreated_ 
Dicyanodiamid_ 
4.31 
.45 
-3.86 
5.51 
.66 
—4." 85 
6.91 
.87 
—6." 04 
8.65 
1.22 
—7.43 
9.83 
1.08 
-8.~75 
12.50 
1.08 
— 11742 
13. 75 
1.29 
-12.46 
Guanylurea sul- 
phate.. 
1.17 
-3.14 
2.12 
-3.39 
3.03 
-3.88 
4.65 
-4.00 
7.73 
-2.10 
11. 72 
-.78 
17.40 
3. 65 
Ammonium sul- 
phate__ 
10.64 
6.33 
23.01 
17.50 
25.26 
18.35 
26.88 
18.23 
27.39 
17.56 
29.65 
17.15 
30.27 
16. 52 
The retarding effect of dicyanodiamid upon the nitrification processes was very 
striking. Not only was the dicyanodiamid not converted into nitrates but at the 
concentration used it almost completely stopped the nitrification of the nitrogen 
present in the soil organic matter. At the end of 210 days the soil with dicyano¬ 
diamid contained 1.29 mgm. of nitrate nitrogen per 100 gm. of air-dried soil as 
contrasted with 13.75 mgm. in the untreated soil. At the beginning of the 
experiment the soil contained 0.56 mgm. nitrate nitrogen. If we consider the 
nitrification of the organic matter in the untreated soil as 100 per cent then th® 
dicyanodiamid retarded the nitrification of the soil nitrogen to the extent of 94.5 
per cent. 
Guanylurea sulphate likewise not only failed to nitrify readily but partially 
prevented the nitrification of the soil nitrogen. The injurious effect was greatest 
at first. After 154 days the nitrate accumulation was nearly as great in the pres¬ 
ence of the guanylurea as in the untreated soil. At the end of 210 days this 
material showed a nitrification of 17.5 per cent. These results would indicate 
that eventually guanylurea sulphate is transformed in the soil to nitrate nitrogen 
but the process is so slow that the material can not be considered as a fertilizer. 
In considering the injurious effects on nitrification noted in these experiments 
it should be borne in mind that the quantities of guanylurea required to produce 
the injury were far in excess of any ever likely to be found under field conditions. 
THE RATE OF DECOMPOSITION OF VARYING QUANTITIES OF DICYANODIAMID 
From the work reported above it seemed that dicyanodiamid was not nitrified 
in the soil even after a considerable period of time. In order to obtain further 
data on this point experiments were made using smaller quantities of the 
material and both ammonia and nitrate determinations were made at intervals. 
In analyzing the samples 25 gm. were taken for each ammonia determination 
while the remainder of the sample was extracted with 500 cc. of water, filtered 
and the dicyanodiamid nitrogen determined in 50 cc. aliquots, nitrates being 
determined by the reduction method in 100 cc. aliquots. The method for 
dicyanodiamid was tested prior to starting the experiments by analyzing several 
soil samples containing different known quantities of dicyanodiamid. The 
average recovery was 98.12 per cent with extreme limits of 95.93 and 99.34 per 
cent. The data, given in Table X, and shown diagrammatically in figure 8, repre¬ 
sent the averages of duplicate determinations in the case of ammonia and nitrate 
nitrogen and the averages of triplicates for dicyanodiamid. The reduction 
method was used for the nitrate determinations. 
