668 
Journal of Agricultural Research 
Vol. xxm, No. 8 
. EFFECT OF AERATION UPON NITROGEN FIXATION 
Flasks containing 250 cc. of media were inoculated with six Azotobacter 
cultures. Altogether, 36 flasks of media were used. Six flasks were inocu¬ 
lated with each respective culture. Three of the flasks for each organism 
were aerated and three were not. Examinations were made on the 
second, fourth, and sixth day. 
The invigorating action of aeration is conclusively shown by these 
data, given in Table I. 
An average of the figures from the six cultures give a net gain of 5.02 
mgm. nitrogen per 100 cc. of the aerated media in two days as compared 
with 0.48 mgm. nitrogen in the nonaerated cultures. In four days the 
comparison indicates an average gain of 8.5 mgm. nitrogen in the aerated 
cultures to 1.24 mgm. nitrogen in the nonaerated cultures. The average 
net gain of the aerated flasks for six days was 10.35 mgm. nitrogen to 
3.25 mgm. nitrogen for the nonaerated cultures. 
Table I .—Effect of aeration upon nitrogen fixation 
Milligrams of nitrogen fixed. 
Culture. 
Aerated cultures. 
Nonaerated cultures. 
2 days. 
4 days. 
6 days. 
2 days. 
4 days. 
6 days. 
1 BM. 
5-3 
8.9 
ii -5 
O 
2. O 
6.6 
3BM. 
4-9 
14. 2 
15-9 
0.34 
I. 2 
6. 0 
222 M. 
6. 0 
8.0 
11. 0 
. 68 
2. I 
6. 0 
10 BP*. 
7. I 
8. 1 
. 2 
. 2 
. 2 
12 BE. 
4.3 
5-6 
8.4 
•7 
• 7 
•7 
525 K. 
4. 6 
7. 2 
7. 2 
0 
. 6 
Average. 
5. 02 
8-5 
10-35 
.48 
1. 24 
3 * 2 5 
It is to be assumed that on account of insufficient surface exposure in 
the nonaerated cultures azofication would be tardy. Nevertheless the 
experiment demonstrates the stimulating effect of aeration and the possi¬ 
bility of cultivating the Azotobacter rapidly in large volumes of media. 
To compare the relative efficiency of this method of aeration with 
shallow depth culture media the following experiment was performed. 
Eighteen 300-cc. flasks containing 50 cc. of dextrose media were inocu¬ 
lated with 0.5 per cent of inoculum of culture 19. These cultures were 
incubated and three flasks were removed for analysis each day for six 
days. Nitrogen determinations were made upon the contents of each of 
two flasks. The third flask was used for sugar analysis. Six 300-cc. 
flasks containing 2 50 cc. of the same media were inoculated with a similar 
proportion of culture and treated to forced aeration. One flask was 
removed each day for nitrogen and sugar determinations. This media 
contained no CaC0 3 . The reaction of the medium was readjusted to a 
P H of 7.0 to 7.4. The results are shown in Table II. 
