June 14, 1924 
Effect of Cyanamid on Microorganisms in Soil 
1161 
FURTHER STUDIES ON THE EFFECT OF CYANAMID AND OTHER NITRO¬ 
GENOUS COMPOUNDS ON BACTERIAL NUMBERS 
In continuation of the work discussed above, a much more comprehensive set 
of experiments was outlined somewhat similar to the. first but using several 
changes in technique suggested by the first experiments. The chief of these was 
the difference in method of incubation of the soil samples. Instead of using a 
large sample of soil and taking samples from the same at intervals, a large num¬ 
ber of small samples of 50 gm. each were incubated in 250 cc. Erlenmeyer flasks. 
This eliminated the many objectionable features and sources of error connected 
with the securing of samples. The mere addition of sterile water to the 50 gm. 
of soil in the flasks, followed by thorough shaking, made the first dilution. 
The soil used was a Clarksville loam which had been in cultivation for several 
years and was rather low in fertility?'. To several 50 gm. portions of the air- 
dried soil in the flasks were added from 5 to 50 mgm. of N in the forms of ammonium 
sulphate, cyanamid (untreated), cyanamid (oiled and hydrated), dicyanodiamid, 
guanylurea sulphate, and urea. After thorough mixing, water was added at the 
rate of 19 cc. per 100 gm. of soil to bring the moisture content up to the optimum. 
In order that the soils might have better air circulation, the flasks were not 
plugged with cotton but kept in an incubator containing a large evaporating 
surface of water which kept the humidity at near saturation. A slow loss of 
moisture did occur, however, and this was restored at intervals. The experi¬ 
ment, which started on June 18, 1921, was continued at room temperature for 
various lengths of time, as shown in Table II. 
Table II.— Numbers of microorganisms in soil following applications of cyanamid 
and related compounds 
Treatment (per 50 gm. of soil) 
Mgm. N 
Millions per gram 
3 days 
7 days 
21 days 
31 days 
38 days 
Control.. ..... 
2.04 
2.09 
1.54 
1.26 
2.60 
Ammonium sulphate___ 
5 
1.86 
1.54 
Lost. 
.76 
1.99 
Do__ 
10 
1.90 
2.08 
.82 
1.25 
1.77 
Do____ 
25 
2.18 
2.45 
.59 
1.70 
2.95 
Do..—__ 
50 
3.91 
5.26 
1.26 
2.52 
3.20 
Cyanamid, untreated.. .. 
5 
2. 58 
4.08 
.98 
1.03 
2.72 
Do.-__ 
10 
5. 52 
4.43 
1.06 
2.23 
2.28 
Do____ 
25 
12.03 
8.63 1 
! .95 
1. 81 
3.95 
Do____ 
50 
14. 57 
6.90 
1.22 
2.81 
2.19 
Cyanamid, oiled and hydrated ... ... 
5 
2.14 
4.30 
1.13 
1.24 
2.47 
Do.—... 
10 
4.68 
2.65 
1.41 
1.58 
3. 37 
Do ... . . .. 
25 
13.44 
7.95 
1.16 
1.69 
3. 72 
Do . - _ _ _ 
50 
14.53 
Lost. 
1.30 
2.30 
3.40 
Dicyanodiamid..... 
5 
3.23 
2.54 
2.51 
1. 55 
2.66 
Do. . . . . 
10 
2.10 
2.65 
2.22 
1.36 
1.72 
Do . .. . . 
25 
2.05 
1.21 
1.75 
1. 51 
1.86 
Do .-... 
1 50 
1. 65 
1.45 
! 1.28 
1. 32 
1.81 
Guanylurea sulphate __ 1 
5 
2.00 
1. 28 
1.28 
1.40 
1.96 
Do .—__ 
10 
2.10 
1.95 
1.03 
1.08 
1.73 
Do-.- ... ... 
25 
2.15 
1.43 
.89 
1.96 
2.18 
Do ..... 
50 
2.68 
1.50 
.93 
1.64 
2.63 
Urea... . . . 
5 
1. 97 
1.28 
.53 
1.30 
1.58 
Do . . . . 
10 
3.05 
1.02 
.50 
1.08 
1 . 70 
Do. . . 
25 
2.76 
1.25 
.62 
1.21 
1 . 72 
Do .. . 
50 
1.99 
1.33 
| .52 
Lost. 
1.74 
