296 
Journal of Agricultural Research 
Vol. XXIV, No 4 
the reaction of samples 6 and 18 in Table VII Azotobacter would not 
be expected to be present. For reasons just discussed, it is probable 
that their presence in these samples is due to the fact that the initial 
hydrogen-ion concentration did not exist sufficiently long to destroy 
them. 
Table VII .—Effect of adding acid to soil containing Azotobacter (soil A) 
Sam¬ 
ple 
No. 
Acid added to 200 gm. soil. 
Ph. 
Azotobacter 
cultures. 
Aug. 22. 
Oct. 10. 
I. 
6.81 
+ 
+ 
2. 
10 cc. 2N sulphuric. 
2. 52 
3 . 
20 cc. 2N sulphuric. 
2. 26 
— 
— 
4 . 
50 cc. 2N sulphuric. 
2. 01 
— 
— 
5 . 
50 cc. 2N sulphuric+io gm. CaCOg. 
1.83 
— 
— 
6. 
10 cc. 2N lactic.. 
5 - 70 
+ 
+ 
7 . 
20 cc. 2N lactic. 
4 - 50 
— 
— 
8. 
50 cc. 2N lactic.. 
4. 06 
— 
— 
9 . 
50 cc. 2N lactic-l-io gm. CaCOg... 
7-03 
+ 
+ 
10.... 
10 cc. 2N lactic. 
6. 46 
+ 
+ 
II.... 
20 cc. 2AT lactic. 
5-09 
+ 
+ 
12.... 
50 cc. 2N lactic. 
3 - 73 
— 
— 
13.... 
50 cc. 2AT lacticH-10 gm. CaCOg. 
6. 00 
+ 
— 
14. ... 
10 cc. 2N formic . 
6. 20 
+ 
+ 
15.... 
20 cc. 2AT formic . 
4. 09 
— 
— 
16. ... 
50 cc. 2N formic . 
3-43 
— 
— 
17. ... 
50 cc. 2N formic+io gm. CaCOg . 
7.78 
+ 
— 
18.... 
10 cc. 2N citric . 
4. 60 
+ 
H- 
% 9 . . .. 
20 cc. 2N citric. .. 
2. 62 
— 
— 
20. ... 
50 cc. 2N citric . 
2. 10 
— 
— 
21.... 
50 cc. 2N citric+io gm. CaCOg .... 
2. 55 
a 4-= Presence of Azotobacter, 
—== Absence of Azotobacter. 
Experiment set up Aug. 6. Moisture content optimum. 
Acidity determined electrometrically. 
The data presented in Table VII indicate that if sufiicient calcium 
carbonate is added to neutralize the added acid the Azotobacter will 
not be affected. However, large quantities of calcium carbonate are in¬ 
effective unless the quantity is sufiicient to maintain a favorable re¬ 
action. 
CONCLUSIONS 
(1) If two soils, one more acid than Pa 6.0 and containing no Azoto¬ 
bacter and the other less acid than Pa 6.0 and containing Azotobacter, 
are mixed in varying proportions, incubated for some time, and cultured 
for Azotobacter, all mixtures giving an acidity less than Pa 6.0 will show 
the presence of Azotobacter, while all cultures very much more acid 
than Pa 6.0 will fail to show Azotobacter. 
(2) If sufiicient calcium carbonate is added to a soil more acid than 
Ph 6.0 and not containing Azotobacter to reduce the hydrogen-ion con¬ 
centration to less than Pa 6.0, the soil will support Azotobacter. 
(3) If sufficient acid is added to a soil less acid than Pa 6.0 and con¬ 
taining Azotobacter to increase the acidity to a ^oint very much greater 
than Pa 6.0, Azotobacter will disappear from the soil, provided this 
acidity exists for sufiicient time to complete their destruction. 
