June 14, 1924 
Effect of Cyanamid on Microorganisms in Soil 
1163 
A STUDY OF THE RELATION OF THE LIME CONTENT OF CYANAMID TO 
THE INCREASE IN BACTERIAL NUMBERS 
Using the same technique as outlined in the preceding experiment, but using 
the Susquehanna loam soil, another experiment was started on March 27, 1922, 
in which cyanamid was applied at different rates and the numbers of bacteria 
developing compared with similar tests where lime was used corresponding to the 
amount in the cyanamid. The three common forms of lime were used, namely, 
the oxid, hydroxid, and carbonate, the amounts being calculated on the basis of 
calcium content. The numbers of colonies which developed on the plates within 
4 da}'s are reported in Table III. 
Table III.— Numbers of microorganisms in soil following applications of cyanamid 
and lime 
Millions per gram 
Treatment (per 50 gm. of soil) 
Mgm. 
3 days 
7 days 
14 days 
21 days 
Control..... 
3.64 
3.01 
2.17 
1.61 
Cyanamid..... 
123 
12.60 
14.00 
27.27 
2.40 
7.60 
247 
8.15 
17.60 
24.65 
Do.... 
493 
3. 46 
}• 24.70 
35.26 
45. 30 
152. 52 
60.20 
.40 
Do....... 
123 
CaCO».... 
570 
1.47 
Cyanamid...... 
247 
} 6.12 
94.53 
30.55 
1. 45 
CaCOj_ _ 
570 
Cyanamid....._. 
493 
} 1.68 
35.20 
69.90 
2.60 
CaCOs..... 
570 
Do..... .... 
143 
4.35 
2.98 
1.39 
2.12 
Do. ... 
285 
5. 82 
4.08 
2.07 
2.13 
Do.... ... 
570 
5. 57 
5.15 
1.93 
1.30 
Ca(OH)j.. .. 
105 
6.05 
10.42 
2.63 
1.17 
Do ... .. 
211 
10.25 
20.38 
14. 53 
5.13 
Do....... 
422 
9.95 
82.73 
30.33 
3.67 
CaO...... 
80 
7.70 
8.01 
2.38 
1.68 
Do.... .... 
160 
7. 70 
20.75 
21.58 
2.48 
Do.... 
319 
27.05 
92.80 
44.40 
3. 57 
It will be noted that cyanamid again produced a very marked increase in bac¬ 
terial numbers, particularly at the largest rate of application. The time re¬ 
quired for the maximum increase was usually 14 days, but this varied slightly 
with the different treatments. Even at the smallest rate of application of cy¬ 
anamid, there were about 13 times as many organisms present after 14 days as in 
the control soil. With the largest application, the increase was 70 times, over 
150 millions per gram having been determined by the plate method. Undoubt¬ 
edly, several millions more were present which did not develop upon the medium 
used. 
The use of calcium carbonate, even though it produced only a comparatively 
small increase in numbers when used by itself, very markedly increased the num¬ 
bers when mixed with the two lower percentages of cyanamid. With the largest 
cj^anamid application, the maximum number was 69.9 millions, as compared with 
152.5 millions with cyanamid alone. It is difficult to explain this variation, but 
it was quite likely due to the high alkalinity. 
The three forms of lime used produced results about as might have been 
expected. Calcium carbonate, being neutral and more or less inert, produced 
only a comparatively small stimulation; the hydroxid, which is basic and quick 
to act, increased the numbers up to 27 times that of the control within seven 
days; the oxid, which is still more active, gave a maximum increase of 31 times. 
If large applications of the oxid are used, as has been done in other experiments 
